GHSA-QCQ2-496W-V96P
Vulnerability from github – Published: 2026-07-09 23:52 – Updated: 2026-07-09 23:52
VLAI
Summary
Mistune: Potential DoS via quadratic-time parsing in parse_link_text
Details
Summary
Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. A relatively small input consisting of repeated [ characters causes significant parsing slowdown.
Affected component
mistune/inline_parser.py → parse_link_text
Description
When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload.
Root cause
The vulnerability stems from a two-loop interaction:
- The outer loop in InlineParser.parse() (inline_parser.py) advances
only 1 character at a time when parse_link() returns None
- Each failed attempt calls parse_link_text() which performs an O(n)
scan to the end of the string looking for a closing ]
- With n consecutive [ characters, this results in O(n) × O(n) = O(n²)
total work
PoC
Run below python script
import mistune
import time
md = mistune.create_markdown()
s = "[" * 6400
t = time.perf_counter()
md(s)
print(time.perf_counter() - t)
Benmark poc Run below code for benchmark
import mistune
import time
md = mistune.create_markdown()
sizes = [100,200,400,800,1600,3200,6400]
for n in sizes:
s = "[" * n
t0 = time.perf_counter()
md(s)
dt = time.perf_counter() - t0
print(f"{n:6d} {dt:.6f}")
Observed behaviour
python3 benchmark.py
100 0.001609
200 0.003207
400 0.012906
800 0.050220
1600 0.197307
3200 0.801172
6400 3.190393
Execution time grows superlinearly, consistent with O(n²) complex
Impact
This can be used as a denial-of-service attack in any application that parses user-supplied Markdown using Mistune, including:
- Web applications (comments, posts, content rendering)
- API services processing Markdown
- Documentation rendering systems
- A small (~6 KB) payload can block CPU for multiple seconds.
Suggested fix
Return the furthest scanned position from parse_link_text even on failure, so the outer loop can skip ahead instead of advancing 1 character at a time
Security Classification
CWE-400: Uncontrolled Resource Consumption Denial of Service (CPU exhaustion)
Severity
{
"affected": [
{
"package": {
"ecosystem": "PyPI",
"name": "mistune"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "3.3.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-49851"
],
"database_specific": {
"cwe_ids": [
"CWE-1333",
"CWE-400"
],
"github_reviewed": true,
"github_reviewed_at": "2026-07-09T23:52:27Z",
"nvd_published_at": "2026-06-24T18:17:18Z",
"severity": "HIGH"
},
"details": "### Summary\nMistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n\u00b2)) behavior in parse_link_text. A relatively small input consisting of repeated [ characters causes significant parsing slowdown.\n\n### Affected component\nmistune/inline_parser.py \u2192 **parse_link_text**\n\n### Description\nWhen parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior.\nAn attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload.\n\n### Root cause\nThe vulnerability stems from a two-loop interaction:\n- The outer loop in `InlineParser.parse()` (inline_parser.py) advances \n only 1 character at a time when parse_link() returns None\n- Each failed attempt calls `parse_link_text()` which performs an O(n) \n scan to the end of the string looking for a closing `]`\n- With n consecutive `[` characters, this results in O(n) \u00d7 O(n) = O(n\u00b2) \n total work\n\n### PoC\nRun below python script\n```\nimport mistune\nimport time\n\nmd = mistune.create_markdown()\n\ns = \"[\" * 6400\n\nt = time.perf_counter()\nmd(s)\nprint(time.perf_counter() - t)\n```\n\u003cimg width=\"2028\" height=\"1277\" alt=\"image\" src=\"https://github.com/user-attachments/assets/15d5bc0b-35f8-4a15-85e0-cbc314a45b06\" /\u003e\n\n**Benmark poc**\nRun below code for benchmark\n```\nimport mistune\nimport time\n\nmd = mistune.create_markdown()\n\nsizes = [100,200,400,800,1600,3200,6400]\n\nfor n in sizes:\n s = \"[\" * n\n\n t0 = time.perf_counter()\n md(s)\n dt = time.perf_counter() - t0\n\n print(f\"{n:6d} {dt:.6f}\")\n```\n\u003cimg width=\"2503\" height=\"1341\" alt=\"image\" src=\"https://github.com/user-attachments/assets/f09a7bbb-6927-4ba2-afb1-444dd913b84e\" /\u003e\n\n\n### Observed behaviour\n```\npython3 benchmark.py \n 100 0.001609\n 200 0.003207\n 400 0.012906\n 800 0.050220\n 1600 0.197307\n 3200 0.801172\n 6400 3.190393\n```\nExecution time grows superlinearly, consistent with O(n\u00b2) complex\n\n### Impact\nThis can be used as a denial-of-service attack in any application that parses user-supplied Markdown using Mistune, including:\n\n- Web applications (comments, posts, content rendering)\n- API services processing Markdown\n- Documentation rendering systems\n- A small (~6 KB) payload can block CPU for multiple seconds.\n\n### Suggested fix\nReturn the furthest scanned position from parse_link_text even on failure, so the outer loop can skip ahead instead of advancing 1 character at a time\n\n### Security Classification\nCWE-400: Uncontrolled Resource Consumption\nDenial of Service (CPU exhaustion)",
"id": "GHSA-qcq2-496w-v96p",
"modified": "2026-07-09T23:52:28Z",
"published": "2026-07-09T23:52:27Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-49851"
},
{
"type": "WEB",
"url": "https://access.redhat.com/security/cve/CVE-2026-49851"
},
{
"type": "WEB",
"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2492304"
},
{
"type": "PACKAGE",
"url": "https://github.com/lepture/mistune"
},
{
"type": "WEB",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49851.json"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": " Mistune: Potential DoS via quadratic-time parsing in parse_link_text"
}
BREW-ADR-VIEWER-CVE-2026-49851 (GHSA-QCQ2-496W-V96P)
Vulnerability from osv_homebrew – Published: 2026-08-13 16:35 – Updated: 2026-09-18 14:56 – Source website
VLAI
Summary
Mistune: Potential DoS via quadratic-time parsing in parse_link_text
Details
Summary
Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. A relatively small input consisting of repeated [ characters causes significant parsing slowdown.
Affected component
mistune/inline_parser.py → parse_link_text
Description
When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload.
Root cause
The vulnerability stems from a two-loop interaction:
- The outer loop in InlineParser.parse() (inline_parser.py) advances
only 1 character at a time when parse_link() returns None
- Each failed attempt calls parse_link_text() which performs an O(n)
scan to the end of the string looking for a closing ]
- With n consecutive [ characters, this results in O(n) × O(n) = O(n²)
total work
PoC
Run below python script
import mistune
import time
md = mistune.create_markdown()
s = "[" * 6400
t = time.perf_counter()
md(s)
print(time.perf_counter() - t)
Benmark poc Run below code for benchmark
import mistune
import time
md = mistune.create_markdown()
sizes = [100,200,400,800,1600,3200,6400]
for n in sizes:
s = "[" * n
t0 = time.perf_counter()
md(s)
dt = time.perf_counter() - t0
print(f"{n:6d} {dt:.6f}")
Observed behaviour
python3 benchmark.py
100 0.001609
200 0.003207
400 0.012906
800 0.050220
1600 0.197307
3200 0.801172
6400 3.190393
Execution time grows superlinearly, consistent with O(n²) complex
Impact
This can be used as a denial-of-service attack in any application that parses user-supplied Markdown using Mistune, including:
- Web applications (comments, posts, content rendering)
- API services processing Markdown
- Documentation rendering systems
- A small (~6 KB) payload can block CPU for multiple seconds.
Suggested fix
Return the furthest scanned position from parse_link_text even on failure, so the outer loop can skip ahead instead of advancing 1 character at a time
Security Classification
CWE-400: Uncontrolled Resource Consumption Denial of Service (CPU exhaustion)
Severity
References
{
"affected": [
{
"ecosystem_specific": {
"fix": "bump",
"range_state": "fixed",
"resource": "mistune",
"resource_purl": "pkg:pypi/mistune@3.3.4",
"upstream_fixed_in": "3.3.0"
},
"package": {
"ecosystem": "Homebrew",
"name": "adr-viewer",
"purl": "pkg:brew/adr-viewer"
},
"ranges": [
{
"events": [
{
"introduced": "1.3.0"
},
{
"fixed": "1.4.0_6"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"database_specific": {
"confidence": "high",
"source": "matched",
"strategy": "registry",
"upstream_evidence": [
{
"ecosystem": "PyPI",
"key": "pkg:pypi/mistune@3.3.4",
"name": "mistune",
"resource": "mistune",
"strategy": "registry",
"subject_version": "3.3.4"
}
]
},
"details": "### Summary\nMistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n\u00b2)) behavior in parse_link_text. A relatively small input consisting of repeated [ characters causes significant parsing slowdown.\n\n### Affected component\nmistune/inline_parser.py \u2192 **parse_link_text**\n\n### Description\nWhen parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior.\nAn attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload.\n\n### Root cause\nThe vulnerability stems from a two-loop interaction:\n- The outer loop in `InlineParser.parse()` (inline_parser.py) advances \n only 1 character at a time when parse_link() returns None\n- Each failed attempt calls `parse_link_text()` which performs an O(n) \n scan to the end of the string looking for a closing `]`\n- With n consecutive `[` characters, this results in O(n) \u00d7 O(n) = O(n\u00b2) \n total work\n\n### PoC\nRun below python script\n```\nimport mistune\nimport time\n\nmd = mistune.create_markdown()\n\ns = \"[\" * 6400\n\nt = time.perf_counter()\nmd(s)\nprint(time.perf_counter() - t)\n```\n\u003cimg width=\"2028\" height=\"1277\" alt=\"image\" src=\"https://github.com/user-attachments/assets/15d5bc0b-35f8-4a15-85e0-cbc314a45b06\" /\u003e\n\n**Benmark poc**\nRun below code for benchmark\n```\nimport mistune\nimport time\n\nmd = mistune.create_markdown()\n\nsizes = [100,200,400,800,1600,3200,6400]\n\nfor n in sizes:\n s = \"[\" * n\n\n t0 = time.perf_counter()\n md(s)\n dt = time.perf_counter() - t0\n\n print(f\"{n:6d} {dt:.6f}\")\n```\n\u003cimg width=\"2503\" height=\"1341\" alt=\"image\" src=\"https://github.com/user-attachments/assets/f09a7bbb-6927-4ba2-afb1-444dd913b84e\" /\u003e\n\n\n### Observed behaviour\n```\npython3 benchmark.py \n 100 0.001609\n 200 0.003207\n 400 0.012906\n 800 0.050220\n 1600 0.197307\n 3200 0.801172\n 6400 3.190393\n```\nExecution time grows superlinearly, consistent with O(n\u00b2) complex\n\n### Impact\nThis can be used as a denial-of-service attack in any application that parses user-supplied Markdown using Mistune, including:\n\n- Web applications (comments, posts, content rendering)\n- API services processing Markdown\n- Documentation rendering systems\n- A small (~6 KB) payload can block CPU for multiple seconds.\n\n### Suggested fix\nReturn the furthest scanned position from parse_link_text even on failure, so the outer loop can skip ahead instead of advancing 1 character at a time\n\n### Security Classification\nCWE-400: Uncontrolled Resource Consumption\nDenial of Service (CPU exhaustion)",
"id": "BREW-adr-viewer-CVE-2026-49851",
"modified": "2026-09-18T14:56:30Z",
"published": "2026-08-13T16:35:11Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-49851"
},
{
"type": "WEB",
"url": "https://access.redhat.com/security/cve/CVE-2026-49851"
},
{
"type": "WEB",
"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2492304"
},
{
"type": "PACKAGE",
"url": "https://github.com/lepture/mistune"
},
{
"type": "WEB",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49851.json"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": " Mistune: Potential DoS via quadratic-time parsing in parse_link_text",
"upstream": [
"GHSA-qcq2-496w-v96p",
"CVE-2026-49851",
"PYSEC-2026-2652"
]
}
BREW-BUKU-CVE-2026-49851 (GHSA-QCQ2-496W-V96P)
Vulnerability from osv_homebrew – Published: 2026-08-13 16:38 – Updated: 2026-09-18 15:06 – Source website
VLAI
Summary
Mistune: Potential DoS via quadratic-time parsing in parse_link_text
Details
Summary
Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. A relatively small input consisting of repeated [ characters causes significant parsing slowdown.
Affected component
mistune/inline_parser.py → parse_link_text
Description
When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload.
Root cause
The vulnerability stems from a two-loop interaction:
- The outer loop in InlineParser.parse() (inline_parser.py) advances
only 1 character at a time when parse_link() returns None
- Each failed attempt calls parse_link_text() which performs an O(n)
scan to the end of the string looking for a closing ]
- With n consecutive [ characters, this results in O(n) × O(n) = O(n²)
total work
PoC
Run below python script
import mistune
import time
md = mistune.create_markdown()
s = "[" * 6400
t = time.perf_counter()
md(s)
print(time.perf_counter() - t)
Benmark poc Run below code for benchmark
import mistune
import time
md = mistune.create_markdown()
sizes = [100,200,400,800,1600,3200,6400]
for n in sizes:
s = "[" * n
t0 = time.perf_counter()
md(s)
dt = time.perf_counter() - t0
print(f"{n:6d} {dt:.6f}")
Observed behaviour
python3 benchmark.py
100 0.001609
200 0.003207
400 0.012906
800 0.050220
1600 0.197307
3200 0.801172
6400 3.190393
Execution time grows superlinearly, consistent with O(n²) complex
Impact
This can be used as a denial-of-service attack in any application that parses user-supplied Markdown using Mistune, including:
- Web applications (comments, posts, content rendering)
- API services processing Markdown
- Documentation rendering systems
- A small (~6 KB) payload can block CPU for multiple seconds.
Suggested fix
Return the furthest scanned position from parse_link_text even on failure, so the outer loop can skip ahead instead of advancing 1 character at a time
Security Classification
CWE-400: Uncontrolled Resource Consumption Denial of Service (CPU exhaustion)
Severity
References
| URL | Type | |||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
||||||||||||||||||||
{
"affected": [
{
"ecosystem_specific": {
"fix": "bump",
"range_state": "fixed",
"resource": "mistune",
"resource_purl": "pkg:pypi/mistune@3.3.4",
"upstream_fixed_in": "3.3.0"
},
"package": {
"ecosystem": "Homebrew",
"name": "buku",
"purl": "pkg:brew/buku"
},
"ranges": [
{
"events": [
{
"introduced": "5.1"
},
{
"fixed": "5.1_6"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"database_specific": {
"confidence": "high",
"source": "matched",
"strategy": "registry",
"upstream_evidence": [
{
"ecosystem": "PyPI",
"key": "pkg:pypi/mistune@3.3.4",
"name": "mistune",
"resource": "mistune",
"strategy": "registry",
"subject_version": "3.3.4"
}
]
},
"details": "### Summary\nMistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n\u00b2)) behavior in parse_link_text. A relatively small input consisting of repeated [ characters causes significant parsing slowdown.\n\n### Affected component\nmistune/inline_parser.py \u2192 **parse_link_text**\n\n### Description\nWhen parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior.\nAn attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload.\n\n### Root cause\nThe vulnerability stems from a two-loop interaction:\n- The outer loop in `InlineParser.parse()` (inline_parser.py) advances \n only 1 character at a time when parse_link() returns None\n- Each failed attempt calls `parse_link_text()` which performs an O(n) \n scan to the end of the string looking for a closing `]`\n- With n consecutive `[` characters, this results in O(n) \u00d7 O(n) = O(n\u00b2) \n total work\n\n### PoC\nRun below python script\n```\nimport mistune\nimport time\n\nmd = mistune.create_markdown()\n\ns = \"[\" * 6400\n\nt = time.perf_counter()\nmd(s)\nprint(time.perf_counter() - t)\n```\n\u003cimg width=\"2028\" height=\"1277\" alt=\"image\" src=\"https://github.com/user-attachments/assets/15d5bc0b-35f8-4a15-85e0-cbc314a45b06\" /\u003e\n\n**Benmark poc**\nRun below code for benchmark\n```\nimport mistune\nimport time\n\nmd = mistune.create_markdown()\n\nsizes = [100,200,400,800,1600,3200,6400]\n\nfor n in sizes:\n s = \"[\" * n\n\n t0 = time.perf_counter()\n md(s)\n dt = time.perf_counter() - t0\n\n print(f\"{n:6d} {dt:.6f}\")\n```\n\u003cimg width=\"2503\" height=\"1341\" alt=\"image\" src=\"https://github.com/user-attachments/assets/f09a7bbb-6927-4ba2-afb1-444dd913b84e\" /\u003e\n\n\n### Observed behaviour\n```\npython3 benchmark.py \n 100 0.001609\n 200 0.003207\n 400 0.012906\n 800 0.050220\n 1600 0.197307\n 3200 0.801172\n 6400 3.190393\n```\nExecution time grows superlinearly, consistent with O(n\u00b2) complex\n\n### Impact\nThis can be used as a denial-of-service attack in any application that parses user-supplied Markdown using Mistune, including:\n\n- Web applications (comments, posts, content rendering)\n- API services processing Markdown\n- Documentation rendering systems\n- A small (~6 KB) payload can block CPU for multiple seconds.\n\n### Suggested fix\nReturn the furthest scanned position from parse_link_text even on failure, so the outer loop can skip ahead instead of advancing 1 character at a time\n\n### Security Classification\nCWE-400: Uncontrolled Resource Consumption\nDenial of Service (CPU exhaustion)",
"id": "BREW-buku-CVE-2026-49851",
"modified": "2026-09-18T15:06:13Z",
"published": "2026-08-13T16:38:25Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-49851"
},
{
"type": "WEB",
"url": "https://access.redhat.com/security/cve/CVE-2026-49851"
},
{
"type": "WEB",
"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2492304"
},
{
"type": "PACKAGE",
"url": "https://github.com/lepture/mistune"
},
{
"type": "WEB",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49851.json"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": " Mistune: Potential DoS via quadratic-time parsing in parse_link_text",
"upstream": [
"GHSA-qcq2-496w-v96p",
"CVE-2026-49851",
"PYSEC-2026-2652"
]
}
BREW-IREDIS-CVE-2026-49851 (GHSA-QCQ2-496W-V96P)
Vulnerability from osv_homebrew – Published: 2026-08-13 17:00 – Updated: 2026-09-17 17:45 – Source website
VLAI
Summary
Mistune: Potential DoS via quadratic-time parsing in parse_link_text
Details
Summary
Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. A relatively small input consisting of repeated [ characters causes significant parsing slowdown.
Affected component
mistune/inline_parser.py → parse_link_text
Description
When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload.
Root cause
The vulnerability stems from a two-loop interaction:
- The outer loop in InlineParser.parse() (inline_parser.py) advances
only 1 character at a time when parse_link() returns None
- Each failed attempt calls parse_link_text() which performs an O(n)
scan to the end of the string looking for a closing ]
- With n consecutive [ characters, this results in O(n) × O(n) = O(n²)
total work
PoC
Run below python script
import mistune
import time
md = mistune.create_markdown()
s = "[" * 6400
t = time.perf_counter()
md(s)
print(time.perf_counter() - t)
Benmark poc Run below code for benchmark
import mistune
import time
md = mistune.create_markdown()
sizes = [100,200,400,800,1600,3200,6400]
for n in sizes:
s = "[" * n
t0 = time.perf_counter()
md(s)
dt = time.perf_counter() - t0
print(f"{n:6d} {dt:.6f}")
Observed behaviour
python3 benchmark.py
100 0.001609
200 0.003207
400 0.012906
800 0.050220
1600 0.197307
3200 0.801172
6400 3.190393
Execution time grows superlinearly, consistent with O(n²) complex
Impact
This can be used as a denial-of-service attack in any application that parses user-supplied Markdown using Mistune, including:
- Web applications (comments, posts, content rendering)
- API services processing Markdown
- Documentation rendering systems
- A small (~6 KB) payload can block CPU for multiple seconds.
Suggested fix
Return the furthest scanned position from parse_link_text even on failure, so the outer loop can skip ahead instead of advancing 1 character at a time
Security Classification
CWE-400: Uncontrolled Resource Consumption Denial of Service (CPU exhaustion)
Severity
References
| URL | Type | |||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
||||||||||||||||||||
{
"affected": [
{
"ecosystem_specific": {
"fix": "bump",
"range_state": "fixed",
"resource": "mistune",
"resource_purl": "pkg:pypi/mistune@3.3.3",
"upstream_fixed_in": "3.3.0"
},
"package": {
"ecosystem": "Homebrew",
"name": "iredis",
"purl": "pkg:brew/iredis"
},
"ranges": [
{
"events": [
{
"introduced": "1.9.4"
},
{
"fixed": "1.16.1_3"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"database_specific": {
"confidence": "high",
"source": "matched",
"strategy": "registry",
"upstream_evidence": [
{
"ecosystem": "PyPI",
"key": "pkg:pypi/mistune@3.3.3",
"name": "mistune",
"resource": "mistune",
"strategy": "registry",
"subject_version": "3.3.3"
}
]
},
"details": "### Summary\nMistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n\u00b2)) behavior in parse_link_text. A relatively small input consisting of repeated [ characters causes significant parsing slowdown.\n\n### Affected component\nmistune/inline_parser.py \u2192 **parse_link_text**\n\n### Description\nWhen parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior.\nAn attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload.\n\n### Root cause\nThe vulnerability stems from a two-loop interaction:\n- The outer loop in `InlineParser.parse()` (inline_parser.py) advances \n only 1 character at a time when parse_link() returns None\n- Each failed attempt calls `parse_link_text()` which performs an O(n) \n scan to the end of the string looking for a closing `]`\n- With n consecutive `[` characters, this results in O(n) \u00d7 O(n) = O(n\u00b2) \n total work\n\n### PoC\nRun below python script\n```\nimport mistune\nimport time\n\nmd = mistune.create_markdown()\n\ns = \"[\" * 6400\n\nt = time.perf_counter()\nmd(s)\nprint(time.perf_counter() - t)\n```\n\u003cimg width=\"2028\" height=\"1277\" alt=\"image\" src=\"https://github.com/user-attachments/assets/15d5bc0b-35f8-4a15-85e0-cbc314a45b06\" /\u003e\n\n**Benmark poc**\nRun below code for benchmark\n```\nimport mistune\nimport time\n\nmd = mistune.create_markdown()\n\nsizes = [100,200,400,800,1600,3200,6400]\n\nfor n in sizes:\n s = \"[\" * n\n\n t0 = time.perf_counter()\n md(s)\n dt = time.perf_counter() - t0\n\n print(f\"{n:6d} {dt:.6f}\")\n```\n\u003cimg width=\"2503\" height=\"1341\" alt=\"image\" src=\"https://github.com/user-attachments/assets/f09a7bbb-6927-4ba2-afb1-444dd913b84e\" /\u003e\n\n\n### Observed behaviour\n```\npython3 benchmark.py \n 100 0.001609\n 200 0.003207\n 400 0.012906\n 800 0.050220\n 1600 0.197307\n 3200 0.801172\n 6400 3.190393\n```\nExecution time grows superlinearly, consistent with O(n\u00b2) complex\n\n### Impact\nThis can be used as a denial-of-service attack in any application that parses user-supplied Markdown using Mistune, including:\n\n- Web applications (comments, posts, content rendering)\n- API services processing Markdown\n- Documentation rendering systems\n- A small (~6 KB) payload can block CPU for multiple seconds.\n\n### Suggested fix\nReturn the furthest scanned position from parse_link_text even on failure, so the outer loop can skip ahead instead of advancing 1 character at a time\n\n### Security Classification\nCWE-400: Uncontrolled Resource Consumption\nDenial of Service (CPU exhaustion)",
"id": "BREW-iredis-CVE-2026-49851",
"modified": "2026-09-17T17:45:16Z",
"published": "2026-08-13T17:00:03Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-49851"
},
{
"type": "WEB",
"url": "https://access.redhat.com/security/cve/CVE-2026-49851"
},
{
"type": "WEB",
"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2492304"
},
{
"type": "PACKAGE",
"url": "https://github.com/lepture/mistune"
},
{
"type": "WEB",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49851.json"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": " Mistune: Potential DoS via quadratic-time parsing in parse_link_text",
"upstream": [
"GHSA-qcq2-496w-v96p",
"CVE-2026-49851",
"PYSEC-2026-2652"
]
}
BREW-JIRATUI-CVE-2026-49851 (GHSA-QCQ2-496W-V96P)
Vulnerability from osv_homebrew – Published: 2026-08-13 17:00 – Updated: 2026-09-17 18:51 – Source website
VLAI
Summary
Mistune: Potential DoS via quadratic-time parsing in parse_link_text
Details
Summary
Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. A relatively small input consisting of repeated [ characters causes significant parsing slowdown.
Affected component
mistune/inline_parser.py → parse_link_text
Description
When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload.
Root cause
The vulnerability stems from a two-loop interaction:
- The outer loop in InlineParser.parse() (inline_parser.py) advances
only 1 character at a time when parse_link() returns None
- Each failed attempt calls parse_link_text() which performs an O(n)
scan to the end of the string looking for a closing ]
- With n consecutive [ characters, this results in O(n) × O(n) = O(n²)
total work
PoC
Run below python script
import mistune
import time
md = mistune.create_markdown()
s = "[" * 6400
t = time.perf_counter()
md(s)
print(time.perf_counter() - t)
Benmark poc Run below code for benchmark
import mistune
import time
md = mistune.create_markdown()
sizes = [100,200,400,800,1600,3200,6400]
for n in sizes:
s = "[" * n
t0 = time.perf_counter()
md(s)
dt = time.perf_counter() - t0
print(f"{n:6d} {dt:.6f}")
Observed behaviour
python3 benchmark.py
100 0.001609
200 0.003207
400 0.012906
800 0.050220
1600 0.197307
3200 0.801172
6400 3.190393
Execution time grows superlinearly, consistent with O(n²) complex
Impact
This can be used as a denial-of-service attack in any application that parses user-supplied Markdown using Mistune, including:
- Web applications (comments, posts, content rendering)
- API services processing Markdown
- Documentation rendering systems
- A small (~6 KB) payload can block CPU for multiple seconds.
Suggested fix
Return the furthest scanned position from parse_link_text even on failure, so the outer loop can skip ahead instead of advancing 1 character at a time
Security Classification
CWE-400: Uncontrolled Resource Consumption Denial of Service (CPU exhaustion)
Severity
References
| URL | Type | |||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
||||||||||||||||||||
{
"affected": [
{
"ecosystem_specific": {
"fix": "bump",
"range_state": "fixed",
"resource": "mistune",
"resource_purl": "pkg:pypi/mistune@3.3.4",
"upstream_fixed_in": "3.3.0"
},
"package": {
"ecosystem": "Homebrew",
"name": "jiratui",
"purl": "pkg:brew/jiratui"
},
"ranges": [
{
"events": [
{
"introduced": "1.8.0"
},
{
"fixed": "1.10.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"database_specific": {
"confidence": "high",
"source": "matched",
"strategy": "registry",
"upstream_evidence": [
{
"ecosystem": "PyPI",
"key": "pkg:pypi/mistune@3.3.4",
"name": "mistune",
"resource": "mistune",
"strategy": "registry",
"subject_version": "3.3.4"
}
]
},
"details": "### Summary\nMistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n\u00b2)) behavior in parse_link_text. A relatively small input consisting of repeated [ characters causes significant parsing slowdown.\n\n### Affected component\nmistune/inline_parser.py \u2192 **parse_link_text**\n\n### Description\nWhen parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior.\nAn attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload.\n\n### Root cause\nThe vulnerability stems from a two-loop interaction:\n- The outer loop in `InlineParser.parse()` (inline_parser.py) advances \n only 1 character at a time when parse_link() returns None\n- Each failed attempt calls `parse_link_text()` which performs an O(n) \n scan to the end of the string looking for a closing `]`\n- With n consecutive `[` characters, this results in O(n) \u00d7 O(n) = O(n\u00b2) \n total work\n\n### PoC\nRun below python script\n```\nimport mistune\nimport time\n\nmd = mistune.create_markdown()\n\ns = \"[\" * 6400\n\nt = time.perf_counter()\nmd(s)\nprint(time.perf_counter() - t)\n```\n\u003cimg width=\"2028\" height=\"1277\" alt=\"image\" src=\"https://github.com/user-attachments/assets/15d5bc0b-35f8-4a15-85e0-cbc314a45b06\" /\u003e\n\n**Benmark poc**\nRun below code for benchmark\n```\nimport mistune\nimport time\n\nmd = mistune.create_markdown()\n\nsizes = [100,200,400,800,1600,3200,6400]\n\nfor n in sizes:\n s = \"[\" * n\n\n t0 = time.perf_counter()\n md(s)\n dt = time.perf_counter() - t0\n\n print(f\"{n:6d} {dt:.6f}\")\n```\n\u003cimg width=\"2503\" height=\"1341\" alt=\"image\" src=\"https://github.com/user-attachments/assets/f09a7bbb-6927-4ba2-afb1-444dd913b84e\" /\u003e\n\n\n### Observed behaviour\n```\npython3 benchmark.py \n 100 0.001609\n 200 0.003207\n 400 0.012906\n 800 0.050220\n 1600 0.197307\n 3200 0.801172\n 6400 3.190393\n```\nExecution time grows superlinearly, consistent with O(n\u00b2) complex\n\n### Impact\nThis can be used as a denial-of-service attack in any application that parses user-supplied Markdown using Mistune, including:\n\n- Web applications (comments, posts, content rendering)\n- API services processing Markdown\n- Documentation rendering systems\n- A small (~6 KB) payload can block CPU for multiple seconds.\n\n### Suggested fix\nReturn the furthest scanned position from parse_link_text even on failure, so the outer loop can skip ahead instead of advancing 1 character at a time\n\n### Security Classification\nCWE-400: Uncontrolled Resource Consumption\nDenial of Service (CPU exhaustion)",
"id": "BREW-jiratui-CVE-2026-49851",
"modified": "2026-09-17T18:51:24Z",
"published": "2026-08-13T17:00:58Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-49851"
},
{
"type": "WEB",
"url": "https://access.redhat.com/security/cve/CVE-2026-49851"
},
{
"type": "WEB",
"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2492304"
},
{
"type": "PACKAGE",
"url": "https://github.com/lepture/mistune"
},
{
"type": "WEB",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49851.json"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": " Mistune: Potential DoS via quadratic-time parsing in parse_link_text",
"upstream": [
"GHSA-qcq2-496w-v96p",
"CVE-2026-49851",
"PYSEC-2026-2652"
]
}
BREW-JUPYTERLAB-CVE-2026-49851 (GHSA-QCQ2-496W-V96P)
Vulnerability from osv_homebrew – Published: 2026-08-13 17:01 – Updated: 2026-09-17 19:02 – Source website
VLAI
Summary
Mistune: Potential DoS via quadratic-time parsing in parse_link_text
Details
Summary
Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. A relatively small input consisting of repeated [ characters causes significant parsing slowdown.
Affected component
mistune/inline_parser.py → parse_link_text
Description
When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload.
Root cause
The vulnerability stems from a two-loop interaction:
- The outer loop in InlineParser.parse() (inline_parser.py) advances
only 1 character at a time when parse_link() returns None
- Each failed attempt calls parse_link_text() which performs an O(n)
scan to the end of the string looking for a closing ]
- With n consecutive [ characters, this results in O(n) × O(n) = O(n²)
total work
PoC
Run below python script
import mistune
import time
md = mistune.create_markdown()
s = "[" * 6400
t = time.perf_counter()
md(s)
print(time.perf_counter() - t)
Benmark poc Run below code for benchmark
import mistune
import time
md = mistune.create_markdown()
sizes = [100,200,400,800,1600,3200,6400]
for n in sizes:
s = "[" * n
t0 = time.perf_counter()
md(s)
dt = time.perf_counter() - t0
print(f"{n:6d} {dt:.6f}")
Observed behaviour
python3 benchmark.py
100 0.001609
200 0.003207
400 0.012906
800 0.050220
1600 0.197307
3200 0.801172
6400 3.190393
Execution time grows superlinearly, consistent with O(n²) complex
Impact
This can be used as a denial-of-service attack in any application that parses user-supplied Markdown using Mistune, including:
- Web applications (comments, posts, content rendering)
- API services processing Markdown
- Documentation rendering systems
- A small (~6 KB) payload can block CPU for multiple seconds.
Suggested fix
Return the furthest scanned position from parse_link_text even on failure, so the outer loop can skip ahead instead of advancing 1 character at a time
Security Classification
CWE-400: Uncontrolled Resource Consumption Denial of Service (CPU exhaustion)
Severity
References
| URL | Type | |||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
||||||||||||||||||||
{
"affected": [
{
"ecosystem_specific": {
"fix": "bump",
"range_state": "fixed",
"resource": "mistune",
"resource_purl": "pkg:pypi/mistune@3.3.4",
"upstream_fixed_in": "3.3.0"
},
"package": {
"ecosystem": "Homebrew",
"name": "jupyterlab",
"purl": "pkg:brew/jupyterlab"
},
"ranges": [
{
"events": [
{
"introduced": "1.2.0"
},
{
"fixed": "4.6.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"database_specific": {
"confidence": "high",
"source": "matched",
"strategy": "registry",
"upstream_evidence": [
{
"ecosystem": "PyPI",
"key": "pkg:pypi/mistune@3.3.4",
"name": "mistune",
"resource": "mistune",
"strategy": "registry",
"subject_version": "3.3.4"
}
]
},
"details": "### Summary\nMistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n\u00b2)) behavior in parse_link_text. A relatively small input consisting of repeated [ characters causes significant parsing slowdown.\n\n### Affected component\nmistune/inline_parser.py \u2192 **parse_link_text**\n\n### Description\nWhen parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior.\nAn attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload.\n\n### Root cause\nThe vulnerability stems from a two-loop interaction:\n- The outer loop in `InlineParser.parse()` (inline_parser.py) advances \n only 1 character at a time when parse_link() returns None\n- Each failed attempt calls `parse_link_text()` which performs an O(n) \n scan to the end of the string looking for a closing `]`\n- With n consecutive `[` characters, this results in O(n) \u00d7 O(n) = O(n\u00b2) \n total work\n\n### PoC\nRun below python script\n```\nimport mistune\nimport time\n\nmd = mistune.create_markdown()\n\ns = \"[\" * 6400\n\nt = time.perf_counter()\nmd(s)\nprint(time.perf_counter() - t)\n```\n\u003cimg width=\"2028\" height=\"1277\" alt=\"image\" src=\"https://github.com/user-attachments/assets/15d5bc0b-35f8-4a15-85e0-cbc314a45b06\" /\u003e\n\n**Benmark poc**\nRun below code for benchmark\n```\nimport mistune\nimport time\n\nmd = mistune.create_markdown()\n\nsizes = [100,200,400,800,1600,3200,6400]\n\nfor n in sizes:\n s = \"[\" * n\n\n t0 = time.perf_counter()\n md(s)\n dt = time.perf_counter() - t0\n\n print(f\"{n:6d} {dt:.6f}\")\n```\n\u003cimg width=\"2503\" height=\"1341\" alt=\"image\" src=\"https://github.com/user-attachments/assets/f09a7bbb-6927-4ba2-afb1-444dd913b84e\" /\u003e\n\n\n### Observed behaviour\n```\npython3 benchmark.py \n 100 0.001609\n 200 0.003207\n 400 0.012906\n 800 0.050220\n 1600 0.197307\n 3200 0.801172\n 6400 3.190393\n```\nExecution time grows superlinearly, consistent with O(n\u00b2) complex\n\n### Impact\nThis can be used as a denial-of-service attack in any application that parses user-supplied Markdown using Mistune, including:\n\n- Web applications (comments, posts, content rendering)\n- API services processing Markdown\n- Documentation rendering systems\n- A small (~6 KB) payload can block CPU for multiple seconds.\n\n### Suggested fix\nReturn the furthest scanned position from parse_link_text even on failure, so the outer loop can skip ahead instead of advancing 1 character at a time\n\n### Security Classification\nCWE-400: Uncontrolled Resource Consumption\nDenial of Service (CPU exhaustion)",
"id": "BREW-jupyterlab-CVE-2026-49851",
"modified": "2026-09-17T19:02:18Z",
"published": "2026-08-13T17:01:18Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-49851"
},
{
"type": "WEB",
"url": "https://access.redhat.com/security/cve/CVE-2026-49851"
},
{
"type": "WEB",
"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2492304"
},
{
"type": "PACKAGE",
"url": "https://github.com/lepture/mistune"
},
{
"type": "WEB",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49851.json"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": " Mistune: Potential DoS via quadratic-time parsing in parse_link_text",
"upstream": [
"GHSA-qcq2-496w-v96p",
"CVE-2026-49851",
"PYSEC-2026-2652"
]
}
BREW-RECON-NG-CVE-2026-49851 (GHSA-QCQ2-496W-V96P)
Vulnerability from osv_homebrew – Published: 2026-08-13 17:32 – Updated: 2026-09-10 01:05 – Source website
VLAI
Summary
Mistune: Potential DoS via quadratic-time parsing in parse_link_text
Details
Summary
Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. A relatively small input consisting of repeated [ characters causes significant parsing slowdown.
Affected component
mistune/inline_parser.py → parse_link_text
Description
When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload.
Root cause
The vulnerability stems from a two-loop interaction:
- The outer loop in InlineParser.parse() (inline_parser.py) advances
only 1 character at a time when parse_link() returns None
- Each failed attempt calls parse_link_text() which performs an O(n)
scan to the end of the string looking for a closing ]
- With n consecutive [ characters, this results in O(n) × O(n) = O(n²)
total work
PoC
Run below python script
import mistune
import time
md = mistune.create_markdown()
s = "[" * 6400
t = time.perf_counter()
md(s)
print(time.perf_counter() - t)
Benmark poc Run below code for benchmark
import mistune
import time
md = mistune.create_markdown()
sizes = [100,200,400,800,1600,3200,6400]
for n in sizes:
s = "[" * n
t0 = time.perf_counter()
md(s)
dt = time.perf_counter() - t0
print(f"{n:6d} {dt:.6f}")
Observed behaviour
python3 benchmark.py
100 0.001609
200 0.003207
400 0.012906
800 0.050220
1600 0.197307
3200 0.801172
6400 3.190393
Execution time grows superlinearly, consistent with O(n²) complex
Impact
This can be used as a denial-of-service attack in any application that parses user-supplied Markdown using Mistune, including:
- Web applications (comments, posts, content rendering)
- API services processing Markdown
- Documentation rendering systems
- A small (~6 KB) payload can block CPU for multiple seconds.
Suggested fix
Return the furthest scanned position from parse_link_text even on failure, so the outer loop can skip ahead instead of advancing 1 character at a time
Security Classification
CWE-400: Uncontrolled Resource Consumption Denial of Service (CPU exhaustion)
Severity
References
| URL | Type | |||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
||||||||||||||||||||
{
"affected": [
{
"ecosystem_specific": {
"fix": null,
"range_state": "affected",
"resource": "mistune",
"resource_purl": "pkg:pypi/mistune@3.1.4",
"upstream_fixed_in": "3.3.0"
},
"package": {
"ecosystem": "Homebrew",
"name": "recon-ng",
"purl": "pkg:brew/recon-ng"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"database_specific": {
"confidence": "high",
"source": "matched",
"strategy": "registry",
"upstream_evidence": [
{
"ecosystem": "PyPI",
"key": "pkg:pypi/mistune@3.1.4",
"name": "mistune",
"resource": "mistune",
"strategy": "registry",
"subject_version": "3.1.4"
}
]
},
"details": "### Summary\nMistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n\u00b2)) behavior in parse_link_text. A relatively small input consisting of repeated [ characters causes significant parsing slowdown.\n\n### Affected component\nmistune/inline_parser.py \u2192 **parse_link_text**\n\n### Description\nWhen parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior.\nAn attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload.\n\n### Root cause\nThe vulnerability stems from a two-loop interaction:\n- The outer loop in `InlineParser.parse()` (inline_parser.py) advances \n only 1 character at a time when parse_link() returns None\n- Each failed attempt calls `parse_link_text()` which performs an O(n) \n scan to the end of the string looking for a closing `]`\n- With n consecutive `[` characters, this results in O(n) \u00d7 O(n) = O(n\u00b2) \n total work\n\n### PoC\nRun below python script\n```\nimport mistune\nimport time\n\nmd = mistune.create_markdown()\n\ns = \"[\" * 6400\n\nt = time.perf_counter()\nmd(s)\nprint(time.perf_counter() - t)\n```\n\u003cimg width=\"2028\" height=\"1277\" alt=\"image\" src=\"https://github.com/user-attachments/assets/15d5bc0b-35f8-4a15-85e0-cbc314a45b06\" /\u003e\n\n**Benmark poc**\nRun below code for benchmark\n```\nimport mistune\nimport time\n\nmd = mistune.create_markdown()\n\nsizes = [100,200,400,800,1600,3200,6400]\n\nfor n in sizes:\n s = \"[\" * n\n\n t0 = time.perf_counter()\n md(s)\n dt = time.perf_counter() - t0\n\n print(f\"{n:6d} {dt:.6f}\")\n```\n\u003cimg width=\"2503\" height=\"1341\" alt=\"image\" src=\"https://github.com/user-attachments/assets/f09a7bbb-6927-4ba2-afb1-444dd913b84e\" /\u003e\n\n\n### Observed behaviour\n```\npython3 benchmark.py \n 100 0.001609\n 200 0.003207\n 400 0.012906\n 800 0.050220\n 1600 0.197307\n 3200 0.801172\n 6400 3.190393\n```\nExecution time grows superlinearly, consistent with O(n\u00b2) complex\n\n### Impact\nThis can be used as a denial-of-service attack in any application that parses user-supplied Markdown using Mistune, including:\n\n- Web applications (comments, posts, content rendering)\n- API services processing Markdown\n- Documentation rendering systems\n- A small (~6 KB) payload can block CPU for multiple seconds.\n\n### Suggested fix\nReturn the furthest scanned position from parse_link_text even on failure, so the outer loop can skip ahead instead of advancing 1 character at a time\n\n### Security Classification\nCWE-400: Uncontrolled Resource Consumption\nDenial of Service (CPU exhaustion)",
"id": "BREW-recon-ng-CVE-2026-49851",
"modified": "2026-09-10T01:05:54Z",
"published": "2026-08-13T17:32:25Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-49851"
},
{
"type": "WEB",
"url": "https://access.redhat.com/security/cve/CVE-2026-49851"
},
{
"type": "WEB",
"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2492304"
},
{
"type": "PACKAGE",
"url": "https://github.com/lepture/mistune"
},
{
"type": "WEB",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49851.json"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": " Mistune: Potential DoS via quadratic-time parsing in parse_link_text",
"upstream": [
"GHSA-qcq2-496w-v96p",
"CVE-2026-49851",
"PYSEC-2026-2652"
]
}
CVE-2026-49851 (GCVE-0-2026-49851)
Vulnerability from cvelistv5 – Published: 2026-06-24 17:05 – Updated: 2026-08-28 12:04
VLAI
EPSS
VEX
Title
Mistune: Potential DoS via quadratic-time parsing in parse_link_text
Summary
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0.
Severity
SSVC
Exploitation: poc
Automatable: yes
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-06-25 19:55 UTC
CWE
Assigner
References
5 references
| URL | Tags |
|---|---|
| https://github.com/lepture/mistune/security/advis… | x_refsource_CONFIRM |
| https://access.redhat.com/security/cve/CVE-2026-49851 | vdb-entryx_refsource_REDHAT |
| https://bugzilla.redhat.com/show_bug.cgi?id=2492304 | issue-trackingx_refsource_REDHAT |
| https://security.access.redhat.com/data/csaf/v2/v… | x_sadp-csaf-vex |
| https://access.redhat.com/errata/RHSA-2026:60520 | vendor-advisoryx_refsource_REDHAT |
Impacted products
23 products
| Vendor | Product | Version | |
|---|---|---|---|
| lepture | mistune |
Affected:
< 3.3.0
|
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787073866 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787073936 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787073873 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787073459 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787073611 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787073451 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787076778 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787077779 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787076481 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787074331 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787073913 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787074078 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787073929 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787073605 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787073546 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787073717 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787073713 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Red Hat OpenShift AI 3.4 |
Unaffected:
1787073593 , < *
(rpm)
cpe:/a:redhat:openshift_ai:3.4::el9 |
|
| Red Hat | Migration Toolkit for Applications 8 |
cpe:/a:redhat:migration_toolkit_applications:8
|
|
| Red Hat | Red Hat OpenShift AI (RHOAI) |
cpe:/a:redhat:openshift_ai
|
|
| Red Hat | Red Hat OpenShift Container Platform 4 |
cpe:/a:redhat:openshift:4
|
|
| Red Hat | Red Hat Satellite 6 |
cpe:/a:redhat:satellite:6
|
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"content": {
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"options": [
{
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},
{
"Automatable": "yes"
},
{
"Technical Impact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-06-25T19:55:32.245725Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2026-06-25T19:55:45.423Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"references": [
{
"tags": [
"exploit"
],
"url": "https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p"
}
],
"title": "CISA ADP Vulnrichment"
},
{
"affected": [
{
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"cpes": [
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"product": "Red Hat OpenShift AI 3.4",
"vendor": "Red Hat",
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"cpes": [
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"title": "Mistune: Mistune: Denial of Service via crafted Markdown input",
"workarounds": [
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"value": "Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability."
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"cna": {
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"product": "mistune",
"vendor": "lepture",
"versions": [
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"version": "\u003c 3.3.0"
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"value": "Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n\u00b2)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0."
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"title": "Mistune: Potential DoS via quadratic-time parsing in parse_link_text"
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"datePublished": "2026-06-24T17:05:33.602Z",
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PYSEC-2026-2652
Vulnerability from pysec - Published: 2026-07-13 15:46 - Updated: 2026-07-13 16:04
VLAI
Details
Summary
Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. A relatively small input consisting of repeated [ characters causes significant parsing slowdown.
Affected component
mistune/inline_parser.py → parse_link_text
Description
When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload.
Root cause
The vulnerability stems from a two-loop interaction:
- The outer loop in InlineParser.parse() (inline_parser.py) advances
only 1 character at a time when parse_link() returns None
- Each failed attempt calls parse_link_text() which performs an O(n)
scan to the end of the string looking for a closing ]
- With n consecutive [ characters, this results in O(n) × O(n) = O(n²)
total work
PoC
Run below python script
import mistune
import time
md = mistune.create_markdown()
s = "[" * 6400
t = time.perf_counter()
md(s)
print(time.perf_counter() - t)
Benmark poc Run below code for benchmark
import mistune
import time
md = mistune.create_markdown()
sizes = [100,200,400,800,1600,3200,6400]
for n in sizes:
s = "[" * n
t0 = time.perf_counter()
md(s)
dt = time.perf_counter() - t0
print(f"{n:6d} {dt:.6f}")
Observed behaviour
python3 benchmark.py
100 0.001609
200 0.003207
400 0.012906
800 0.050220
1600 0.197307
3200 0.801172
6400 3.190393
Execution time grows superlinearly, consistent with O(n²) complex
Impact
This can be used as a denial-of-service attack in any application that parses user-supplied Markdown using Mistune, including:
- Web applications (comments, posts, content rendering)
- API services processing Markdown
- Documentation rendering systems
- A small (~6 KB) payload can block CPU for multiple seconds.
Suggested fix
Return the furthest scanned position from parse_link_text even on failure, so the outer loop can skip ahead instead of advancing 1 character at a time
Security Classification
CWE-400: Uncontrolled Resource Consumption Denial of Service (CPU exhaustion)
Severity
Impacted products
| Name | purl | mistune | pkg:pypi/mistune |
|---|
Aliases
{
"affected": [
{
"package": {
"ecosystem": "PyPI",
"name": "mistune",
"purl": "pkg:pypi/mistune"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "3.3.0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"0.1.0",
"0.2.0",
"0.3.0",
"0.3.1",
"0.4",
"0.4.1",
"0.5",
"0.5.1",
"0.6",
"0.7",
"0.7.1",
"0.7.2",
"0.7.3",
"0.7.4",
"0.8",
"0.8.1",
"0.8.2",
"0.8.3",
"0.8.4",
"2.0.0",
"2.0.0a1",
"2.0.0a2",
"2.0.0a3",
"2.0.0a4",
"2.0.0a5",
"2.0.0a6",
"2.0.0rc1",
"2.0.1",
"2.0.2",
"2.0.3",
"2.0.4",
"2.0.5",
"2.1.0",
"3.0.0",
"3.0.0a1",
"3.0.0a2",
"3.0.0a3",
"3.0.0rc1",
"3.0.0rc2",
"3.0.0rc3",
"3.0.0rc4",
"3.0.0rc5",
"3.0.1",
"3.0.2",
"3.1.0",
"3.1.1",
"3.1.2",
"3.1.3",
"3.1.4",
"3.2.0",
"3.2.1"
]
}
],
"aliases": [
"CVE-2026-49851",
"GHSA-qcq2-496w-v96p"
],
"details": "### Summary\nMistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n\u00b2)) behavior in parse_link_text. A relatively small input consisting of repeated [ characters causes significant parsing slowdown.\n\n### Affected component\nmistune/inline_parser.py \u2192 **parse_link_text**\n\n### Description\nWhen parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior.\nAn attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload.\n\n### Root cause\nThe vulnerability stems from a two-loop interaction:\n- The outer loop in `InlineParser.parse()` (inline_parser.py) advances \n only 1 character at a time when parse_link() returns None\n- Each failed attempt calls `parse_link_text()` which performs an O(n) \n scan to the end of the string looking for a closing `]`\n- With n consecutive `[` characters, this results in O(n) \u00d7 O(n) = O(n\u00b2) \n total work\n\n### PoC\nRun below python script\n```\nimport mistune\nimport time\n\nmd = mistune.create_markdown()\n\ns = \"[\" * 6400\n\nt = time.perf_counter()\nmd(s)\nprint(time.perf_counter() - t)\n```\n\u003cimg width=\"2028\" height=\"1277\" alt=\"image\" src=\"https://github.com/user-attachments/assets/15d5bc0b-35f8-4a15-85e0-cbc314a45b06\" /\u003e\n\n**Benmark poc**\nRun below code for benchmark\n```\nimport mistune\nimport time\n\nmd = mistune.create_markdown()\n\nsizes = [100,200,400,800,1600,3200,6400]\n\nfor n in sizes:\n s = \"[\" * n\n\n t0 = time.perf_counter()\n md(s)\n dt = time.perf_counter() - t0\n\n print(f\"{n:6d} {dt:.6f}\")\n```\n\u003cimg width=\"2503\" height=\"1341\" alt=\"image\" src=\"https://github.com/user-attachments/assets/f09a7bbb-6927-4ba2-afb1-444dd913b84e\" /\u003e\n\n\n### Observed behaviour\n```\npython3 benchmark.py \n 100 0.001609\n 200 0.003207\n 400 0.012906\n 800 0.050220\n 1600 0.197307\n 3200 0.801172\n 6400 3.190393\n```\nExecution time grows superlinearly, consistent with O(n\u00b2) complex\n\n### Impact\nThis can be used as a denial-of-service attack in any application that parses user-supplied Markdown using Mistune, including:\n\n- Web applications (comments, posts, content rendering)\n- API services processing Markdown\n- Documentation rendering systems\n- A small (~6 KB) payload can block CPU for multiple seconds.\n\n### Suggested fix\nReturn the furthest scanned position from parse_link_text even on failure, so the outer loop can skip ahead instead of advancing 1 character at a time\n\n### Security Classification\nCWE-400: Uncontrolled Resource Consumption\nDenial of Service (CPU exhaustion)",
"id": "PYSEC-2026-2652",
"modified": "2026-07-13T16:04:52.376795Z",
"published": "2026-07-13T15:46:30.641314Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-49851"
},
{
"type": "WEB",
"url": "https://access.redhat.com/security/cve/CVE-2026-49851"
},
{
"type": "WEB",
"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2492304"
},
{
"type": "PACKAGE",
"url": "https://github.com/lepture/mistune"
},
{
"type": "WEB",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49851.json"
},
{
"type": "PACKAGE",
"url": "https://pypi.org/project/mistune"
},
{
"type": "ADVISORY",
"url": "https://github.com/advisories/GHSA-qcq2-496w-v96p"
}
],
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": " Mistune: Potential DoS via quadratic-time parsing in parse_link_text"
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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