PostCSS up to 8.5.11 PreviousMap process path traversal

Summaryinfo

A vulnerability, which was classified as critical, was found in PostCSS up to 8.5.11. This vulnerability affects the function process of the component PreviousMap. Executing a manipulation can lead to path traversal. This vulnerability appears as CVE-2026-45623. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability classified as critical was found in PostCSS up to 8.5.11. This vulnerability affects the function process of the component PreviousMap. The manipulation with an unknown input leads to a path traversal vulnerability. The CWE definition for the vulnerability is 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. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

PostCSS takes a CSS file and provides an API to analyze and modify its rules by transforming the rules into an Abstract Syntax Tree. In versions 8.5.11 and prior, the PreviousMap parses the /*# sourceMappingURL=PATH */ comment from any CSS string passed to process() and dereferences PATH against the local filesystem with no scheme, allowlist, or traversal check. An attacker who controls the CSS input can cause the host process to read any file readable by Node and leak the first ~10 bytes of its content through the resulting JSON.parse SyntaxError message. The bug also yields a precise file-existence oracle and a controllable-read primitive that may be combined with large-file targets for DoS. The behaviour is triggered with PostCSS's default options — no from, no map, no plugins required — and is therefore reachable from any pipeline that runs untrusted CSS through PostCSS (CMS themes, user-uploaded styles, browser-extension/userstyle processors, build pipelines for third-party packages, blog comment renderers, etc.). This issue has been fixed in version 8.5.12.

The advisory is available at github.com. This vulnerability was named CVE-2026-45623 since 05/12/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1006 by the MITRE ATT&CK project.

Upgrading to version 8.5.12 eliminates this vulnerability.

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Productinfo

Name

• PostCSS

Version

• 8.5.0
• 8.5.1
• 8.5.2
• 8.5.3
• 8.5.4
• 8.5.5
• 8.5.6
• 8.5.7
• 8.5.8
• 8.5.9
• 8.5.10
• 8.5.11

Website

• Product: https://github.com/postcss/postcss/

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