What is CVE-2026-40261?

CVE-2026-40261 is a high-severity vulnerability in Composer, classified under OS Command Injection. CVSS score: 8.8/10. Published 2026-04-15.

How severe is CVE-2026-40261?

High severity. CVSS v3 base score is 8.8 out of 10.

Is CVE-2026-40261 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

RCE in Composer

CVE-2026-40261

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 w…

Vulnerability class: Command Injection (OS Command Injection)

EPSS: 0.001 (15.8th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 8.8 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H.

Affected products

Composer — versions >= 2.3.0, < 2.9.6, >= 1.0.0, < 2.2.27

Weakness classification (CWE)

Public proof-of-concept exploits

terminat0r7031/composer-CVE-2026-40261-CVE-2026-40176-PoC

References

https://github.com/composer/composer/security/advisories/GHSA-gqw4-4w2p-838q (x_refsource_CONFIRM)
https://github.com/composer/composer/releases/tag/2.9.6 (x_refsource_MISC)

Frequently asked questions

What is CVE-2026-40261?: CVE-2026-40261 is a high-severity vulnerability in Composer, classified under OS Command Injection. CVSS score: 8.8/10. Published 2026-04-15.
How severe is CVE-2026-40261?: High severity. CVSS v3 base score is 8.8 out of 10.
Is CVE-2026-40261 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.