What’s Vulnerable › Vulnerabilities

CVE-2026-73646: PostCSS: Path Traversal in Previous Source Map Auto-Loading (sourceMappingURL) leads to Arbitrary .map File Disclosure

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-17 · updated 2026-09-18
• Weakness: CWE-22

Description

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 products

• Npm Postcss: before 8.5.18 — fixed in 8.5.18
• postcss: before 8.5.18

How to fix

Upgrade to a fixed version: Npm Postcss 8.5.18. Check the vendor advisory for mitigations.

References

• https://github.com/postcss/postcss/commit/95663d3eb7ba26f4854dd19d3b4f4425760cf56c
• https://github.com/postcss/postcss/releases/tag/8.5.18
• https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849
• https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849

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