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CVE-2026-40261 high CVSS 8.8

Vulnerability in composer/composer (CVE-2026-40261)

Summary

Vulnerability in composer/composer (CVE-2026-40261). Successful exploitation can lead to full system takeover. Mitigation: upgrade to 2.2.27 or later.

Original description

The description as published by the source.

Composer is a dependency manager for PHP. Versions 1.0 through 2.2.26 and 2.3 through 2.9.5 contain a command injection vulnerability in the Perforce::syncCodeBase() method, which appends the $sourceReference parameter to a shell command without proper escaping, and additionally in the Perforce::generateP4Command() method as in GHSA-wg36-wvj6-r67p / CVE-2026-40176, which interpolates user-supplied Perforce connection parameters (port, user, client) from the source url field without proper escaping. An attacker can inject arbitrary commands through crafted source reference or source url values containing shell metacharacters, even if Perforce is not installed. Unlike CVE-2026-40176, the source reference and url are provided as part of package metadata, meaning any compromised or malicious Composer repository can serve package metadata declaring perforce as a source type with malicious values. This vulnerability is exploitable when installing or updating dependencies from source, including the default behavior when installing dev-prefixed versions. This issue has been fixed in Composer 2.2.27 (2.2 LTS) and 2.9.6 (mainline). If developers are unable to immediately update, they can avoid installing dependencies from source by using --prefer-dist or the preferred-install: dist config setting, and only use trusted Composer repositories as a workaround.

Source: NIST National Vulnerability Database 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-2026-40261 has been found in composer/composer.
Successful exploitation can lead to full system takeover. CVSS score: 8.8/10.
What to do: upgrade composer/composer to 2.2.27 or later.
If unsure, ask your IT team or search "composer/composer CVE-2026-40261" on the vendor's site.

CVE-2026-40261 (composer/composer) — CWE-20 / CVSS v3 8.8
Attack vector: remote (network-reachable) / unauthenticated
Patched: 2.2.27 — 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-20) exists in composer/composer.

📍 Affected scope

Check the vendor advisory for the affected versions of composer/composer.

🔥 Severity

Severity: High (CVSS 8.8/10). Successful exploitation can lead to full system takeover.

🔧 How to fix

Update to 2.2.27.

🛡️ 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 'composer/composer' . 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 'composer/composer' . | 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 composer/composer 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 composer/composer to 2.2.27

    ステージング環境で 2.2.27 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

composer composer/composer
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.2.27"}]}]
Bitnami composer
[{"type":"SEMVER","events":[{"introduced":"1.0.0"},{"fixed":"2.2.27"},{"introduced":"2.3.0"},{"fixed":"2.9.6"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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