# 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.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Aug 2026
- **Updated:** 17 Aug 2026
- **Also known as:** CLEANSTART-2026-FN09185, CLEANSTART-2026-WV03334, CLSA-2026-1784856450, CLSA-2026-1787592261, CLSA-2026-1790019520, CLSA-2026-1790023229, CLSA-2026-1790023231, CLSA-2026-1790089248, CLSA-2026-1790089252, CLSA-2026-1790089264, CLSA-2026-1790089280, CLSA-2026-1790089282, CLSA-2026-1790099843, CLSA-2026-1790102697, CLSA-2026-1790541900, CLSA-2026-1791377049, CLSA-2026-1791377114, CLSA-2026-1793097120, CLSA-2026-1793097204, DEBIAN-CVE-2026-73646, ECHO-d855-bcfe-6381, GHSA-r28c-9q8g-f849, MINI-4pgw-7fwq-96xv, MINI-578f-rmwq-4hx8, MINI-72gp-786w-q7cf, MINI-f38w-p3cr-rqq5, MINI-jq3p-m659-5r76, MINI-jwm9-25c4-vcfw, MINI-q5m5-qrqc-76mf, MINI-qcv9-mxg5-qpgx, MINI-qf5q-jmcm-cxgx, MINI-vqrg-4mvv-92q5, MINI-xxfg-mhq2-jxp2, ROOT-APP-NPM-CVE-2026-73646, ROOT-APP-NPM-GHSA-r28c-9q8g-f849, UBUNTU-CVE-2026-73646

## 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 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2026-73646?

2 open source packages ship an affected version, including postcss.


| Package | Ecosystem | 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.

## Is CVE-2026-73646 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-73646 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-73646 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-73646 exists.

Affected packages and fixed versions:
- postcss (npm): affected all versions; fixed in 8.5.18
- postcss (npm): affected all versions; fixed in 8.5.18

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-73646/ (Markdown: https://insights.sbomify.com/CVE-2026-73646/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-73646
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-73646
- OSV: https://osv.dev/vulnerability/CVE-2026-73646

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-73646/
Summaries are generated and may contain mistakes; the official description above is the record.