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CVE-2026-73646 high CVSS 7.5

Path Traversal in postcss (CVE-2026-73646)

Summary

Path traversal in postcss (CVE-2026-73646). Confidential information can be exposed externally. Exploitable via loadFile. Mitigation: upgrade to 8.5.18 or later.

Original description

The description as published by the source.

Vulnerability Details

File: lib/previous-map.js
Line: 87-98 (loadFile), 129-144 (loadMap)

Root Cause

PostCSS auto-detects a /*# sourceMappingURL=... */ comment inside the CSS text it is asked to parse and, unless the caller explicitly passes map: false, attempts to load that path from disk as a "previous source map." This happens on every postcss.parse() / postcss().process() call by default (opt-out, not opt-in).

loadMap() builds the candidate path via join(dirname(opts.from), annotation), where annotation is the raw, attacker-controlled string from the CSS comment. path.join() normalizes but does not sandbox .. segments, so a ../../../ prefix walks the resolved path outside the intended directory. If opts.from is not set at all, the annotation is used completely unmodified — an absolute path in the CSS comment is read verbatim.

8.5.12 already fixed a strictly worse variant of this (any file, any extension, could be read) by requiring the resolved path to end in .map (loadFile()). That fix did not address the traversal itself, only the target extension. Since the join(dirname(file), map) logic has existed unchanged since PostCSS 8.0.0 (Feb 2020), any file ending in .map remains readable through this path in the current release (8.5.16).

Once loaded, MapGenerator.isMap() treats the mere presence of a loaded "previous map" as an implicit request to generate result.map, even when the caller never set the map option.…

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-2026-73646 has been found in postcss.
Attackers can target a specific entry point like loadFile over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 7.5/10.
What to do: upgrade postcss to 8.5.18 or later.
If unsure, ask your IT team or search "postcss CVE-2026-73646" on the vendor's site.

CVE-2026-73646 (postcss) — CWE-22 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: loadFile / loadMap / annotation / opts.from
Patched: 8.5.18 — 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 loadFile without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of postcss. Attack surface: loadFile / loadMap / annotation / opts.from.

🔥 Severity

Severity: High (CVSS 7.5/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 8.5.18.

🛡️ 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 8.5.18

    ステージング環境で 8.5.18 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":"8.5.18"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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