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Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') in postcss

CVE-2026-45623

  • postcss
High
9.1/10

Summary

PostCSS's `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 affects versions prior to 8.5.12.

  • LOW
  • NETWORK
  • NONE
  • UNCHANGED
  • NONE
  • NONE
  • HIGH
  • HIGH

CWE-22 - Path Traversal

Path traversal (or directory traversal), is a vulnerability that allows malicious users to traverse the server's root directory, gaining access to arbitrary files and folders such as application code & data, back-end credentials, and sensitive operating system files. In the worst-case scenario, an attacker could potentially execute arbitrary files on the server, resulting in a denial of service attack. Such an exploit may severely impact the integrity, confidentiality, and availability of an application.

References

Advisory Timeline

  • Published