Composer: CVE-2026-59946 fix bypass via symlinked package bin path

Summary

Composer is a dependency Manager for the PHP language. From 1.0 until 2.2.30 and from 2.3.0 until 2.10.3, a malicious or compromised dependency can bypass the earlier CVE-2026-59946 binary-path hardening because Composer validates literal parent-directory segments only during dependency resolution, while the symlink and installed-metadata paths described by the advisory skip that validation. A package can ship an in-package binary symlink that resolves outside its installation directory, or attacker-influenced vendor/composer/installed.json metadata can provide an escaping binary path during a reinstall or regeneration of missing vendor/bin entries. The installed-metadata path is reachable only when the vendor directory was not populated by the same validated install run, such as when it is restored from an untrusted cache, copied from an earlier build stage, carried over from an older Composer run, or writable by a lower-trust build step. Composer can follow the path, change the external target's permissions to make it world-readable and executable, and create a runnable vendor/bin proxy to that external file. The issue does not directly read or transmit data and does not by itself provide remote code execution. This issue is fixed in versions 2.2.30 and 2.10.3.

Timeline

1. Sep 16, 2026, 4:09 PM UTCCVE published
2. Sep 16, 2026, 5:29 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Sep 16, 2026, 5:29 PM UTCRecord last updated

Affected versions

• composer composer

  From 1.0.0 · fixed in 2.2.30; From 2.3.0 · fixed in 2.10.3

• composer/composerPackagist

  From 2.3.0 · fixed in 2.10.3

• composer/composerPackagist

  From 1.0 · fixed in 2.2.30

References 5