Medium [CVE-2026-69153] Information disclosure via crafted sourceMappingURL

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 8.5.19, if from is unset, an attacker can cause PreviousMap.loadFile() to read an unintended source-map file by supplying an absolute or directory-traversal sourceMappingURL.

The resulting map’s sources and sourcesContent may then be exposed to the application. This issue is fixed in version 8.5.19.

A flaw was found in PostCSS. A remote attacker can exploit this vulnerability by providing a specially crafted sourceMappingURL when a specific configuration (the 'from' parameter) is not set.

This can cause the application to read and expose unintended source-map files, potentially revealing sensitive information about the application's source code. Red Hat rates this flaw as Moderate because the information disclosed is limited to files with a.map extension.

Source map files may contain source code paths and content, but the attacker cannot read arbitrary files on the system. Exploitation requires the application to process attacker-controlled CSS through PostCSS on the server side.

Red Hat severity: Moderate — CVSS 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N). Weakness: CWE-22.