CVE-2026-40261
HIGHCVE-2026-40261 is a high-severity (CVSS 8.8) remote code execution vulnerability in composer/composer. O3 Security confirms whether CVE-2026-40261 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Composer has Command Injection via Malicious Perforce Reference
Blast Radius
composer/composer🐘composer/composerReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | composer/composer | ≥ 2.3.0&&< 2.9.6 | 2.9.6 |
| 🐘Packagist | composer/composer | ≥ 1.0.0&&< 2.2.27 | 2.2.27 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for composer/composer. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update composer/composer to 2.9.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-40261 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-40261 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-40261. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-40261 in your dependencies?
O3 detects CVE-2026-40261 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.