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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.3 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-69153: 0.45% estimated exploitation activity in the next 30 days; percentile 39.24 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 nested inside if (cssFile) { ... }. When PostCSS is invoked without the from option, cssFile is falsy and that branch is skipped, leaving only the .map extension check. PreviousMap is constructed by lib/input.js whenever pathAvailable && sourceMapAvailable (under Node with source-map available), independent of opts.from/opts.map (the constructor returns early only for opts.map === false). So postcss([]).process(css) on attacker CSS reaches loadFile with cssFile undefined, and an attacker /

sourceMappingURL=/abs/path/x.map / (or ../-traversing path) is read via readFileSync. When the file is valid JSON, its sources (filesystem paths) and sourcesContent (source contents) are disclosed in the…

Published by the source

3 Aug 2026, 17:11 UTC

Last modified by the source

3 Aug 2026, 17:11 UTC

Source last checked

26 Oct 2026, 13:00 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-fxqj-rqcc-2cmp

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# Patch Next advisory brief: CVE-2026-69153

Advisory: PostCSS: incomplete fix of GHSA-6g55-p6wh-862q — attacker-controlled sourceMappingURL reads arbitrary .map files when `from` is unset
IDs: CVE-2026-69153, GHSA-fxqj-rqcc-2cmp
Record: https://patchnext.com/advisories/cve-2026-69153 (revision 1, source checked 26 Oct 2026, 13:00 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: postcss 8.5.23. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm postcss: affected <= 8.5.22; fixed in 8.5.23

## Suggested inspection (read-only)
- `npm ls postcss --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on postcss.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-fxqj-rqcc-2cmp (GitHub-reviewed advisory GHSA-fxqj-rqcc-2cmp lists affected ranges: npm postcss >=0 <=8.5.22)

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