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CVE-2026-69153 medium CVSS 5.3

Path Traversal in postcss (CVE-2026-69153)

Summary

Path traversal in postcss (CVE-2026-69153). Risk of unauthorized operations or information disclosure. Exploitable via sourceMappingURL. Mitigation: upgrade to 8.5.23 or later.

Original description

The description as published by the source.

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 generated source map.

Affected code (v8.5.22 — the release carrying the GHSA-6g55 fix)

// lib/previous-map.js
loadFile(path, cssFile, trusted) {
  if (!trusted && !this.unsafeMap) {
    if (!/\.map$/i.test(path)) {
      return undefined
    }
    if (cssFile) {                       // guard runs ONLY when `from` is set
      let relativePath = relative(dirname(cssFile), path)
      if (relativePath === '..' ||
          relativePath…

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-2026-69153 has been found in postcss.
Attackers can target a specific entry point like sourceMappingURL over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade postcss to 8.5.23 or later.
If unsure, ask your IT team or search "postcss CVE-2026-69153" on the vendor's site.

CVE-2026-69153 (postcss) — CWE-22 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: sourceMappingURL / from / cssFile / PreviousMap
Patched: 8.5.23 — 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

Path traversal (CWE-22) exists in postcss. Attackers reach the vulnerable code path via sourceMappingURL without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of postcss. Attack surface: sourceMappingURL / from / cssFile / PreviousMap.

🔥 Severity

Severity: Medium (CVSS 5.3/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 8.5.23.

🛡️ 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' . 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' . | 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 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 to 8.5.23

    ステージング環境で 8.5.23 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
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"8.5.23"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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