CVE-2023-43655: Remote Code Execution via web-accessible composer.phar

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-09-29 · updated 2026-06-17
Weakness: CWE-74

Description

Composer is a dependency manager for PHP. Users publishing a composer.phar to a public web-accessible server where the composer.phar can be executed as a php file may be subject to a remote code execution vulnerability if PHP also has `register_argc_argv` enabled in php.ini. Versions 2.6.4, 2.2.22 and 1.10.27 patch this vulnerability. Users are advised to upgrade. Users unable to upgrade should make sure `register_argc_argv` is disabled in php.ini, and avoid publishing composer.phar to the web as this is not best practice.

Affected products

Debian Linux: 10.0
Fedoraproject Fedora: 37, 38
composer: before 1.10.27; from 2.0.0 before 2.2.21; from 2.3.0 before 2.6.4 — fixed in 1.10.27, 2.2.21, 2.6.4
Packagist Composer/Composer: before 1.10.27; from 2.0.0 before 2.2.22; from 2.3.0 before 2.6.4; 1.0.0, 1.0.0-alpha1, 1.0.0-alpha10, 1.0.0-alpha11, 1.0.0-alpha2, 1.0.0-alpha3 (+172) — fixed in 1.10.27, 2.2.22, 2.6.4

How to fix

Upgrade to a fixed version: composer 1.10.27, 2.2.21, 2.6.4; Packagist Composer/Composer 1.10.27, 2.2.22, 2.6.4. Check the vendor advisory for mitigations.

References

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