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CVE-2026-9358 medium CVSS 4.3

Vulnerability in postcss-selector-parser (CVE-2026-9358)

Summary

Vulnerability in postcss-selector-parser (CVE-2026-9358). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 7.1.3 or later.

Original description

The description as published by the source.

A vulnerability was determined in postcss-selector-parser before 6.1.3 and 7.1.1. 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. 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)."

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-9358 has been found in postcss-selector-parser.
Risk of unauthorized operations or information disclosure. CVSS score: 4.3/10.
What to do: upgrade postcss-selector-parser to 7.1.3 or later.
If unsure, ask your IT team or search "postcss-selector-parser CVE-2026-9358" on the vendor's site.

CVE-2026-9358 (postcss-selector-parser) — CWE-404 / CVSS v3 4.3
Attack vector: remote (network-reachable) / unauthenticated
Patched: 7.1.3 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-404) exists in postcss-selector-parser.

📍 Affected scope

Check the vendor advisory for the affected versions of postcss-selector-parser.

🔥 Severity

Severity: Medium (CVSS 4.3/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 7.1.3.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'postcss-selector-parser' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'postcss-selector-parser' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で postcss-selector-parser を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade postcss-selector-parser to 7.1.3

    ステージング環境で 7.1.3 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

npm postcss-selector-parser
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"7.1.3"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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