GHSA-FXQJ-RQCC-2CMP PostCSS: incomplete fix of GHSA-6g55-p6wh-862q — attacker-controlled sourceMappingURL reads arbitrary .map files when `from` is unset

Summary The fix for GHSA-6g55-p6wh-862q added a guard in lib/previous-map.js PreviousMap.loadFile that restricts an attacker-controlled sourceMappingURL from a CSS comment to a .map extension and, for untrusted maps, rejects .. traversal and absolute paths. The traversal/absolute rejection is...