Vulnerability-Lookup

CVE-2026-73646 (GCVE-0-2026-73646)

Vulnerability from cvelistv5 – Published: 2026-08-17 15:35 – Updated: 2026-08-17 16:36

Title

PostCSS: Path Traversal in Previous Source Map Auto-Loading (sourceMappingURL) leads to Arbitrary .map File Disclosure

Summary

PostCSS takes a CSS file and provides an API to analyze and modify its rules by transforming the rules into an Abstract Syntax Tree. Prior to 8.5.18, lib/previous-map.js loadMap() passes attacker-controlled sourceMappingURL values to join(dirname(opts.from), annotation), and loadFile() permits traversed or absolute .map paths, allowing untrusted CSS processed without map: false to disclose sourcesContent from arbitrary reachable .map files through result.map. This issue is fixed in version 8.5.18.

Severity

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

SSVC

Exploitation: poc Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-17 16:35 UTC

CWE

CWE-22 - Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

Assigner

GitHub_M mitre root

References

3 references

URL	Tags
https://github.com/postcss/postcss/security/advis…	x_refsource_CONFIRM
https://github.com/postcss/postcss/commit/95663d3…	x_refsource_MISC
https://github.com/postcss/postcss/releases/tag/8.5.18	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
postcss	postcss	Affected: < 8.5.18	guessed

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-73646",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-08-17T16:35:17.036116Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-08-17T16:36:37.422Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
            ],
            "url": "https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "postcss",
          "vendor": "postcss",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 8.5.18"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "PostCSS takes a CSS file and provides an API to analyze and modify its rules by transforming the rules into an Abstract Syntax Tree. Prior to 8.5.18, lib/previous-map.js loadMap() passes attacker-controlled sourceMappingURL values to join(dirname(opts.from), annotation), and loadFile() permits traversed or absolute .map paths, allowing untrusted CSS processed without map: false to disclose sourcesContent from arbitrary reachable .map files through result.map. This issue is fixed in version 8.5.18."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-22",
              "description": "CWE-22: Improper Limitation of a Pathname to a Restricted Directory (\u0027Path Traversal\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T15:35:13.518Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849"
        },
        {
          "name": "https://github.com/postcss/postcss/commit/95663d3eb7ba26f4854dd19d3b4f4425760cf56c",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/postcss/postcss/commit/95663d3eb7ba26f4854dd19d3b4f4425760cf56c"
        },
        {
          "name": "https://github.com/postcss/postcss/releases/tag/8.5.18",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/postcss/postcss/releases/tag/8.5.18"
        }
      ],
      "source": {
        "advisory": "GHSA-r28c-9q8g-f849",
        "discovery": "UNKNOWN"
      },
      "title": "PostCSS: Path Traversal in Previous Source Map Auto-Loading (sourceMappingURL) leads to Arbitrary .map File Disclosure"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-73646",
    "datePublished": "2026-08-17T15:35:13.518Z",
    "dateReserved": "2026-08-13T14:04:09.604Z",
    "dateUpdated": "2026-08-17T16:36:37.422Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-73646",
      "date": "2026-09-16",
      "epss": "0.00377",
      "percentile": "0.31327"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-73646\",\"sourceIdentifier\":\"security-advisories@github.com\",\"published\":\"2026-08-17T16:17:47.257\",\"lastModified\":\"2026-08-17T17:16:51.660\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"PostCSS takes a CSS file and provides an API to analyze and modify its rules by transforming the rules into an Abstract Syntax Tree. Prior to 8.5.18, lib/previous-map.js loadMap() passes attacker-controlled sourceMappingURL values to join(dirname(opts.from), annotation), and loadFile() permits traversed or absolute .map paths, allowing untrusted CSS processed without map: false to disclose sourcesContent from arbitrary reachable .map files through result.map. This issue is fixed in version 8.5.18.\"}],\"affected\":[{\"source\":\"security-advisories@github.com\",\"affectedData\":[{\"vendor\":\"postcss\",\"product\":\"postcss\",\"versions\":[{\"version\":\"\u003c 8.5.18\",\"status\":\"affected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N\",\"baseScore\":7.5,\"baseSeverity\":\"HIGH\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"HIGH\",\"integrityImpact\":\"NONE\",\"availabilityImpact\":\"NONE\"},\"exploitabilityScore\":3.9,\"impactScore\":3.6}],\"ssvcV203\":[{\"source\":\"134c704f-9b21-4f2e-91b3-4a467353bcc0\",\"ssvcData\":{\"timestamp\":\"2026-08-17T16:35:17.036116Z\",\"id\":\"CVE-2026-73646\",\"options\":[{\"exploitation\":\"poc\"},{\"automatable\":\"yes\"},{\"technicalImpact\":\"partial\"}],\"role\":\"CISA Coordinator\",\"version\":\"2.0.3\"}}]},\"weaknesses\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Secondary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-22\"}]}],\"references\":[{\"url\":\"https://github.com/postcss/postcss/commit/95663d3eb7ba26f4854dd19d3b4f4425760cf56c\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/postcss/postcss/releases/tag/8.5.18\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849\",\"source\":\"134c704f-9b21-4f2e-91b3-4a467353bcc0\"}]}}",
    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-09-11T10:39:50+00:00",
      "cve": "CVE-2026-73646",
      "id": "CVE-2026-73646",
      "initial_release_date": "2026-08-17T15:35:13.518000+00:00",
      "product_status:fixed": "10",
      "product_status:known_affected": "87",
      "product_status:known_not_affected": "294",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "postcss: PostCSS: Information disclosure via path traversal in source map auto-loading",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-73646.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-08-31T16:25:03Z",
      "cve": "CVE-2026-73646",
      "id": "CVE-2026-73646",
      "initial_release_date": "2026-08-21T00:41:21Z",
      "product_status:known_affected": "262",
      "product_status:known_not_affected": "326",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-73646",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-73646.json",
      "version": "3"
    },
    "vulnrichment": {
      "containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-73646\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"poc\"}, {\"Automatable\": \"yes\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-08-17T16:35:17.036116Z\"}}}], \"references\": [{\"url\": \"https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849\", \"tags\": [\"exploit\"]}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-08-17T16:36:25.466Z\"}}], \"cna\": {\"title\": \"PostCSS: Path Traversal in Previous Source Map Auto-Loading (sourceMappingURL) leads to Arbitrary .map File Disclosure\", \"source\": {\"advisory\": \"GHSA-r28c-9q8g-f849\", \"discovery\": \"UNKNOWN\"}, \"metrics\": [{\"cvssV3_1\": {\"scope\": \"UNCHANGED\", \"version\": \"3.1\", \"baseScore\": 7.5, \"attackVector\": \"NETWORK\", \"baseSeverity\": \"HIGH\", \"vectorString\": \"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N\", \"integrityImpact\": \"NONE\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"LOW\", \"availabilityImpact\": \"NONE\", \"privilegesRequired\": \"NONE\", \"confidentialityImpact\": \"HIGH\"}}], \"affected\": [{\"vendor\": \"postcss\", \"product\": \"postcss\", \"versions\": [{\"status\": \"affected\", \"version\": \"\u003c 8.5.18\"}]}], \"references\": [{\"url\": \"https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849\", \"name\": \"https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849\", \"tags\": [\"x_refsource_CONFIRM\"]}, {\"url\": \"https://github.com/postcss/postcss/commit/95663d3eb7ba26f4854dd19d3b4f4425760cf56c\", \"name\": \"https://github.com/postcss/postcss/commit/95663d3eb7ba26f4854dd19d3b4f4425760cf56c\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"https://github.com/postcss/postcss/releases/tag/8.5.18\", \"name\": \"https://github.com/postcss/postcss/releases/tag/8.5.18\", \"tags\": [\"x_refsource_MISC\"]}], \"descriptions\": [{\"lang\": \"en\", \"value\": \"PostCSS takes a CSS file and provides an API to analyze and modify its rules by transforming the rules into an Abstract Syntax Tree. Prior to 8.5.18, lib/previous-map.js loadMap() passes attacker-controlled sourceMappingURL values to join(dirname(opts.from), annotation), and loadFile() permits traversed or absolute .map paths, allowing untrusted CSS processed without map: false to disclose sourcesContent from arbitrary reachable .map files through result.map. This issue is fixed in version 8.5.18.\"}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-22\", \"description\": \"CWE-22: Improper Limitation of a Pathname to a Restricted Directory (\u0027Path Traversal\u0027)\"}]}], \"providerMetadata\": {\"orgId\": \"a0819718-46f1-4df5-94e2-005712e83aaa\", \"shortName\": \"GitHub_M\", \"dateUpdated\": \"2026-08-17T15:35:13.518Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-73646\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-17T16:36:37.422Z\", \"dateReserved\": \"2026-08-13T14:04:09.604Z\", \"assignerOrgId\": \"a0819718-46f1-4df5-94e2-005712e83aaa\", \"datePublished\": \"2026-08-17T15:35:13.518Z\", \"assignerShortName\": \"GitHub_M\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}

FKIE_CVE-2026-73646

Vulnerability from fkie_nvd - Published: 2026-08-17 16:17 - Updated: 2026-08-17 17:16

Severity

7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/postcss/postcss/commit/95663d3eb7ba26f4854dd19d3b4f4425760cf56c
	security-advisories@github.com	https://github.com/postcss/postcss/releases/tag/8.5.18
	security-advisories@github.com	https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "postcss",
          "vendor": "postcss",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 8.5.18"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "PostCSS takes a CSS file and provides an API to analyze and modify its rules by transforming the rules into an Abstract Syntax Tree. Prior to 8.5.18, lib/previous-map.js loadMap() passes attacker-controlled sourceMappingURL values to join(dirname(opts.from), annotation), and loadFile() permits traversed or absolute .map paths, allowing untrusted CSS processed without map: false to disclose sourcesContent from arbitrary reachable .map files through result.map. This issue is fixed in version 8.5.18."
    }
  ],
  "id": "CVE-2026-73646",
  "lastModified": "2026-08-17T17:16:51.660",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-73646",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-08-17T16:35:17.036116Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-08-17T16:17:47.257",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/postcss/postcss/commit/95663d3eb7ba26f4854dd19d3b4f4425760cf56c"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/postcss/postcss/releases/tag/8.5.18"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "url": "https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-22"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-R28C-9Q8G-F849

Vulnerability from github – Published: 2026-07-24 16:24 – Updated: 2026-08-13 17:55

Summary

PostCSS: Path Traversal in Previous Source Map Auto-Loading (sourceMappingURL) leads to Arbitrary .map File Disclosure

Details

Vulnerability Details

File: lib/previous-map.js Line: 87-98 (loadFile), 129-144 (loadMap)

Root Cause

PostCSS auto-detects a /*# sourceMappingURL=... */ comment inside the CSS text it is asked to parse and, unless the caller explicitly passes map: false, attempts to load that path from disk as a "previous source map." This happens on every postcss.parse() / postcss().process() call by default (opt-out, not opt-in).

loadMap() builds the candidate path via join(dirname(opts.from), annotation), where annotation is the raw, attacker-controlled string from the CSS comment. path.join() normalizes but does not sandbox .. segments, so a ../../../ prefix walks the resolved path outside the intended directory. If opts.from is not set at all, the annotation is used completely unmodified — an absolute path in the CSS comment is read verbatim.

8.5.12 already fixed a strictly worse variant of this (any file, any extension, could be read) by requiring the resolved path to end in .map (loadFile()). That fix did not address the traversal itself, only the target extension. Since the join(dirname(file), map) logic has existed unchanged since PostCSS 8.0.0 (Feb 2020), any file ending in .map remains readable through this path in the current release (8.5.16).

Once loaded, MapGenerator.isMap() treats the mere presence of a loaded "previous map" as an implicit request to generate result.map, even when the caller never set the map option. If the loaded map has a sourcesContent field (common for maps emitted by bundlers/transpilers), that content is merged into result.map and returned to the caller — disclosing the traversed-to file's content to whoever supplied the CSS.

Attack Scenario

A service accepts user-submitted CSS and runs it through PostCSS to lint/format/transform it, e.g. postcss().process(userCss, { from: '/app/uploads/user123/input.css', to: '/app/uploads/user123/output.css' }) — idiomatic usage; map option untouched.
Attacker submits CSS containing /*# sourceMappingURL=../../../../some/other/app/dist/bundle.js.map */ (or an absolute path if from is unset).
PostCSS reads that .map file and folds its sourcesContent into result.map.
The service does what most build pipelines do with a truthy result.map — writes it next to the CSS output or returns it via API (source maps are meant to be consumed by browser devtools, so this is commonly public/served).
Attacker retrieves the emitted map and reads out the traversed file's content.

Impact

Disclosure of the contents of arbitrary .map files reachable via path traversal (or absolute path when from is unset) from the process's filesystem. Affects any application processing CSS it does not fully trust without explicitly passing map: false. No authentication or user interaction beyond submitting CSS text is required.

Vulnerable Code

loadFile(path, cssFile, trusted) {
  if (!trusted && !this.unsafeMap) {
    if (!/\.map$/i.test(path)) {
      return undefined
    }
  }
  this.root = dirname(path)
  if (existsSync(path)) {
    this.mapFile = path
    return readFileSync(path, 'utf-8').toString().trim()
  }
}

loadMap(file, prev) {
  ...
  } else if (this.annotation) {
    let map = this.annotation
    if (file) map = join(dirname(file), map)
    let unknown = this.loadFile(map, file, false)
    ...
  }
}

Recommended Fix

Constrain the resolved path to remain inside the CSS file's own directory instead of relying solely on a filename-extension check:

loadFile(path, cssFile, trusted) {
  if (!trusted && !this.unsafeMap) {
    if (!/\.map$/i.test(path)) {
      return undefined
    }
    if (!cssFile) return undefined
    let root = resolve(dirname(cssFile))
    let resolvedPath = resolve(root, path)
    if (resolvedPath !== root && !resolvedPath.startsWith(root + sep)) {
      return undefined
    }
  }
  this.root = dirname(path)
  if (existsSync(path)) {
    this.mapFile = path
    return readFileSync(path, 'utf-8').toString().trim()
  }
}

I've implemented, tested (full existing test suite — 660/660 passing, plus new PoC-based regression checks for both the traversal and legitimate same-directory cases), and can share this fix on request or via a private fork if invited.

Verification

Dynamically confirmed on v8.5.16 (current npm release / repo HEAD) via a standalone Node.js harness against lib/postcss.js: a "secret" .map file placed two directories outside a simulated project directory was read via a crafted sourceMappingURL comment in otherwise-innocuous CSS, with its sourcesContent appearing verbatim in result.map.toString() — with no map option set by the caller. A second harness confirmed the simpler no-from case reads an absolute path directly. A third harness confirmed map: false is the only current workaround. The attached fix branch closes both vectors while keeping all 660 existing unit tests green.

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 8.5.17"
      },
      "package": {
        "ecosystem": "npm",
        "name": "postcss"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "8.5.18"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-73646"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-22"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-24T16:24:55Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "## Vulnerability Details\n\n**File**: `lib/previous-map.js`\n**Line**: 87-98 (`loadFile`), 129-144 (`loadMap`)\n\n\n### Root Cause\nPostCSS auto-detects a `/*# sourceMappingURL=... */` comment inside the CSS text it is asked to parse and, unless the caller explicitly passes `map: false`, attempts to load that path from disk as a \"previous source map.\" This happens on every `postcss.parse()` / `postcss().process()` call by default (opt-out, not opt-in).\n\n`loadMap()` builds the candidate path via `join(dirname(opts.from), annotation)`, where `annotation` is the raw, attacker-controlled string from the CSS comment. `path.join()` normalizes but does not sandbox `..` segments, so a `../../../` prefix walks the resolved path outside the intended directory. If `opts.from` is not set at all, the annotation is used completely unmodified \u2014 an absolute path in the CSS comment is read verbatim.\n\n8.5.12 already fixed a strictly worse variant of this (any file, any extension, could be read) by requiring the resolved path to end in `.map` (`loadFile()`). That fix did not address the traversal itself, only the target extension. Since the `join(dirname(file), map)` logic has existed unchanged since PostCSS 8.0.0 (Feb 2020), any file ending in `.map` remains readable through this path in the current release (8.5.16).\n\nOnce loaded, `MapGenerator.isMap()` treats the mere presence of a loaded \"previous map\" as an implicit request to generate `result.map`, even when the caller never set the `map` option. If the loaded map has a `sourcesContent` field (common for maps emitted by bundlers/transpilers), that content is merged into `result.map` and returned to the caller \u2014 disclosing the traversed-to file\u0027s content to whoever supplied the CSS.\n\n### Attack Scenario\n1. A service accepts user-submitted CSS and runs it through PostCSS to lint/format/transform it, e.g. `postcss().process(userCss, { from: \u0027/app/uploads/user123/input.css\u0027, to: \u0027/app/uploads/user123/output.css\u0027 })` \u2014 idiomatic usage; `map` option untouched.\n2. Attacker submits CSS containing `/*# sourceMappingURL=../../../../some/other/app/dist/bundle.js.map */` (or an absolute path if `from` is unset).\n3. PostCSS reads that `.map` file and folds its `sourcesContent` into `result.map`.\n4. The service does what most build pipelines do with a truthy `result.map` \u2014 writes it next to the CSS output or returns it via API (source maps are meant to be consumed by browser devtools, so this is commonly public/served).\n5. Attacker retrieves the emitted map and reads out the traversed file\u0027s content.\n\n### Impact\nDisclosure of the contents of arbitrary `.map` files reachable via path traversal (or absolute path when `from` is unset) from the process\u0027s filesystem. Affects any application processing CSS it does not fully trust without explicitly passing `map: false`. No authentication or user interaction beyond submitting CSS text is required.\n\n### Vulnerable Code\n```js\nloadFile(path, cssFile, trusted) {\n  if (!trusted \u0026\u0026 !this.unsafeMap) {\n    if (!/\\.map$/i.test(path)) {\n      return undefined\n    }\n  }\n  this.root = dirname(path)\n  if (existsSync(path)) {\n    this.mapFile = path\n    return readFileSync(path, \u0027utf-8\u0027).toString().trim()\n  }\n}\n\nloadMap(file, prev) {\n  ...\n  } else if (this.annotation) {\n    let map = this.annotation\n    if (file) map = join(dirname(file), map)\n    let unknown = this.loadFile(map, file, false)\n    ...\n  }\n}\n```\n\n### Recommended Fix\nConstrain the resolved path to remain inside the CSS file\u0027s own directory instead of relying solely on a filename-extension check:\n```js\nloadFile(path, cssFile, trusted) {\n  if (!trusted \u0026\u0026 !this.unsafeMap) {\n    if (!/\\.map$/i.test(path)) {\n      return undefined\n    }\n    if (!cssFile) return undefined\n    let root = resolve(dirname(cssFile))\n    let resolvedPath = resolve(root, path)\n    if (resolvedPath !== root \u0026\u0026 !resolvedPath.startsWith(root + sep)) {\n      return undefined\n    }\n  }\n  this.root = dirname(path)\n  if (existsSync(path)) {\n    this.mapFile = path\n    return readFileSync(path, \u0027utf-8\u0027).toString().trim()\n  }\n}\n```\nI\u0027ve implemented, tested (full existing test suite \u2014 660/660 passing, plus new PoC-based regression checks for both the traversal and legitimate same-directory cases), and can share this fix on request or via a private fork if invited.\n\n### Verification\nDynamically confirmed on v8.5.16 (current npm release / repo HEAD) via a standalone Node.js harness against `lib/postcss.js`: a \"secret\" `.map` file placed two directories outside a simulated project directory was read via a crafted `sourceMappingURL` comment in otherwise-innocuous CSS, with its `sourcesContent` appearing verbatim in `result.map.toString()` \u2014 with no `map` option set by the caller. A second harness confirmed the simpler no-`from` case reads an absolute path directly. A third harness confirmed `map: false` is the only current workaround. The attached fix branch closes both vectors while keeping all 660 existing unit tests green.",
  "id": "GHSA-r28c-9q8g-f849",
  "modified": "2026-08-13T17:55:54Z",
  "published": "2026-07-24T16:24:55Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849"
    },
    {
      "type": "WEB",
      "url": "https://github.com/postcss/postcss/commit/95663d3eb7ba26f4854dd19d3b4f4425760cf56c"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/postcss/postcss"
    },
    {
      "type": "WEB",
      "url": "https://github.com/postcss/postcss/releases/tag/8.5.18"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "PostCSS: Path Traversal in Previous Source Map Auto-Loading (sourceMappingURL) leads to Arbitrary .map File Disclosure"
}

RHSA-2026:50287

Vulnerability from csaf_redhat - Published: 2026-08-04 16:47 - Updated: 2026-09-16 18:35

Summary

Red Hat Security Advisory: Red Hat Hardened Images RPMs Security Update

Severity

Important

Scope

4 vulnerabilities in this advisory, including CVE-2026-73646.

CVE-2026-73646

A flaw was found in PostCSS. An attacker can exploit a path traversal vulnerability by providing specially crafted `sourceMappingURL` values in untrusted CSS files. This allows the attacker to disclose sensitive `sourcesContent` from arbitrary `.map` files accessible on the system, leading to information disclosure.

7.5 (High)


                
                  CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Fixed: 3 products

https://access.redhat.com/errata/RHSA-2026:50287

Open the full advisory

RHSA-2026:54520

Vulnerability from csaf_redhat - Published: 2026-08-13 10:18 - Updated: 2026-09-16 13:06

Summary

Red Hat Security Advisory: Red Hat Hardened Images RPMs Security Update

Severity

Important

Scope

2 vulnerabilities in this advisory, including CVE-2026-73646.

CVE-2026-73646

7.5 (High)


                
                  CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Fixed: 3 products

https://access.redhat.com/errata/RHSA-2026:54520

Open the full advisory

RHSA-2026:62260

Vulnerability from csaf_redhat - Published: 2026-09-01 18:22 - Updated: 2026-09-16 19:26

Summary

Red Hat Security Advisory: Red Hat OpenShift Dev Spaces 3.30.0 Release.

Severity

Important

Scope

70 vulnerabilities in this advisory, including CVE-2026-73646.

CVE-2026-73646

7.5 (High)


                
                  CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Fixed: 4 products Known not affected: 61 products

https://access.redhat.com/errata/RHSA-2026:62260

Open the full advisory

ubuntu-cve-2026-73646

Vulnerability from osv_ubuntu

Published

2026-08-17 16:17

Modified

2026-08-19 11:11

Summary

Details

Severity

7.5 (High)


                    
                      CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

N/A (UNKNOWN)


                    
                      medium

References

URL

Type

	https://ubuntu.com/security/CVE-2026-73646	REPORT
	https://www.cve.org/CVERecord?id=CVE-2026-73646	REPORT
	https://github.com/postcss/postcss/security/advis…	REPORT

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "node-postcss",
            "binary_version": "6.0.23-3"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:20.04:LTS",
        "name": "node-postcss",
        "purl": "pkg:deb/ubuntu/node-postcss@6.0.23-3?arch=source\u0026distro=focal"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "6.0.23-1",
        "6.0.23-3"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "node-postcss",
            "binary_version": "8.4.6+~cs7.3.21-1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:22.04:LTS",
        "name": "node-postcss",
        "purl": "pkg:deb/ubuntu/node-postcss@8.4.6+~cs7.3.21-1?arch=source\u0026distro=jammy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "8.2.1+~cs5.3.23-8",
        "8.4.5+~cs7.1.51-2",
        "8.4.6+~cs7.3.21-1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "node-postcss",
            "binary_version": "8.4.31+~cs8.0.26-1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:24.04:LTS",
        "name": "node-postcss",
        "purl": "pkg:deb/ubuntu/node-postcss@8.4.31+~cs8.0.26-1?arch=source\u0026distro=noble"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "8.4.20+~cs8.0.23-1",
        "8.4.31+~cs8.0.26-1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "node-postcss",
            "binary_version": "8.5.8+~cs9.3.30-1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:26.04:LTS",
        "name": "node-postcss",
        "purl": "pkg:deb/ubuntu/node-postcss@8.5.8+~cs9.3.30-1?arch=source\u0026distro=resolute"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "8.5.6+~cs9.3.28-1",
        "8.5.8+~cs9.3.30-1"
      ]
    }
  ],
  "aliases": [],
  "details": "PostCSS takes a CSS file and provides an API to analyze and modify its rules by transforming the rules into an Abstract Syntax Tree. Prior to 8.5.18, lib/previous-map.js loadMap() passes attacker-controlled sourceMappingURL values to join(dirname(opts.from), annotation), and loadFile() permits traversed or absolute .map paths, allowing untrusted CSS processed without map: false to disclose sourcesContent from arbitrary reachable .map files through result.map. This issue is fixed in version 8.5.18.",
  "id": "UBUNTU-CVE-2026-73646",
  "modified": "2026-08-19T11:11:14Z",
  "published": "2026-08-17T16:17:00Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://ubuntu.com/security/CVE-2026-73646"
    },
    {
      "type": "REPORT",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-73646"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849"
    }
  ],
  "related": [],
  "schema_version": "1.7.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "medium",
      "type": "Ubuntu"
    }
  ],
  "upstream": [
    "CVE-2026-73646"
  ]
}

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.

Detection rules are retrieved from Rulezet.

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.

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.

Action not permitted

CVE-2026-73646 (GCVE-0-2026-73646)

FKIE_CVE-2026-73646

GHSA-R28C-9Q8G-F849

Vulnerability Details

Root Cause

Attack Scenario

Impact

Vulnerable Code

Recommended Fix

Verification

RHSA-2026:50287

RHSA-2026:54520

RHSA-2026:62260

ubuntu-cve-2026-73646

Vulnerability from osv_ubuntu

Tags

Sightings

Nomenclature

Related by attack behaviour