CVE-2026-73646 PostCSS: Path Traversal in Previous Source Map Auto-Loading (sourceMappingURL) leads to Arbitrary .map File Disclosure
Attackers can disclose source map contents from arbitrary files via malicious sourceMappingURL in untrusted CSS processed by PostCSS.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-73646?
CVE-2026-73646 is a high-severity path traversal vulnerability in postcss, published on 17 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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 8.5.18, lib/previous-map.js loadMap() passes attacker-controlled sourceMappingURL values to join(dirname(opts.from), annotation), and loadFile() permits traversed or absolute .map paths, allowing untrusted CSS processed without map: false to disclose sourcesContent from arbitrary reachable .map files through result.map. This issue is fixed in version 8.5.18.
Weakness: CWE-22
Which versions are affected by CVE-2026-73646?
2 open source packages ship an affected version, including postcss.
| Package | Affected | Fixed in |
|---|---|---|
postcss npm | All versions | 8.5.18 |
postcss npm | All versions | 8.5.18 |
How do I fix CVE-2026-73646?
Upgrade postcss to 8.5.18 or later.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2026-73646 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-73646 exists.
Sources
Also known as CLEANSTART-2026-FN09185, CLEANSTART-2026-WV03334, CLSA-2026-1784856450, CLSA-2026-1787592261, CLSA-2026-1790019520, CLSA-2026-1790023229 and 30 more.