RCE in Composer

CVE-2026-84361

Composer is a dependency Manager for the PHP language. From 1.0 until 2.2.30 and 2.10.3, a malicious dependency package from a custom Composer repository or an untrusted composer.lock file could set source.type to perforce and source.url to an rsh: or jsh: P4PORT value. When the Perforce p4 client was installed and Composer installed the package from source through composer install or composer update, including --prefer-source, Composer\Util\Perforce passed the address to p4 without validation, causing p4 to run a local command with the privileges of the user or CI account. Packagist.org does not permit Perforce source metadata. This issue is fixed in versions 2.2.30 and 2.10.3.

Vulnerability class: Command Injection (OS Command Injection)

Published · last modified .

EPSS exploit prediction

EPSS: 0.005 (44.6th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 45th percentile — 44.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-84361: held from 0.004 to 0.005.

EPSS over last 30 days · oldest: 0.004 · newest: 0.005 · change: +0.001

Affected products

  • Composer — versions >= 1.0, < 2.2.30, >= 2.3.0, < 2.10.3

Weakness classification (CWE)

Public proof-of-concept exploits

References

Frequently asked questions

What is CVE-2026-84361?
CVE-2026-84361 is a vulnerability in Composer, classified under OS Command Injection. Published 2026-09-01.
Is CVE-2026-84361 known to be exploited?
1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.