CVE-2026-73646
Received Received - Intake

Path Traversal in PostCSS CSS Processor

Publication date: 2026-08-17

Last updated on: 2026-08-17

Assigner: GitHub, Inc.

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.

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Meta Information

Published
2026-08-17
Last Modified
2026-08-17
Generated
2026-08-17
AI Q&A
2026-08-17
EPSS Evaluated
N/A
NVD
CVE-2026-73646
EUVD
EUVD-2026-60239

Affected Vendors & Products

Showing 3 associated CPEs
Vendor Product Version / Range
postcss postcss to 8.5.18 (exc)
postcss postcss From 8.5.18 (exc)
postcss postcss 8.5.18

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-22 The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

Attack-Flow Graph

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Executive Summary

CVE-2026-73646 is a path traversal vulnerability in PostCSS versions 8.5.17 and earlier. It allows attackers to disclose arbitrary file contents by crafting a CSS file with a malicious sourceMappingURL comment pointing to sensitive .map files outside the intended directory. The vulnerability occurs because PostCSS does not properly restrict path resolution when loading source maps.

Detection Guidance

Check PostCSS version with npm list postcss or grep "postcss" package.json. If version is 8.5.17 or earlier, the system is vulnerable. Inspect CSS files for /*# sourceMappingURL=...*/ comments pointing to external paths. Use commands like find / -name "*.map" to locate .map files and verify their access permissions.

Impact Analysis

If you process untrusted CSS files without disabling map auto-loading, an attacker could exploit this to read sensitive files on your system. The vulnerability allows disclosure of file contents via the sourcesContent field in source maps, potentially exposing confidential data like configuration files or source code.

Compliance Impact

This vulnerability could lead to unauthorized disclosure of personal or sensitive data, violating GDPR and HIPAA compliance. Exposure of confidential information may result in regulatory penalties, reputational damage, and loss of trust. Organizations must ensure proper input validation and disable map auto-loading for untrusted CSS.

Mitigation Strategies

Upgrade PostCSS to version 8.5.18 or later. Set map: false in processing options to disable automatic source map loading. If source maps are needed, use the unsafeMap option only in trusted contexts. Validate all CSS input paths to prevent path traversal.

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