CVE-2026-59944: Composer: CVE-2026-59946 fix bypass via symlinked package bin path
Summary
A malicious or compromised Composer package could, when installed as a dependency, cause Composer to change the permissions of a file outside that package's own directory and to register a runnable vendor/bin command that points at that outside file. This is a path traversal and link following issue. It is not remote code execution, the attacker gains no ability to read or receive your data directly. The risk is that a file which was readable only by its owner, but modifiable by Composer, can be made world readable and executable, which is enough to expose its contents on a shared or multi tenant host. The earlier hardening from GHSA-gjfg-22fp-rrxx can be bypassed, since it only rejected literal .. path segments in a package's declared binaries, and was only applied in a single place during dependency resolution.
Am I affected?
You can be affected if a malicious or compromised package, including a transitive dependency, is installed in your project, and either of the following is true:
- The dependency package ships one of its declared binaries as a symbolic link that resolves to a location outside the package's own directory. Nothing beyond a normal install or update is required. - Or, the recorded metadata of your installed dependencies (vendor/composer/installed.json) declares a binary path that escapes the package's directory. Composer regenerates missing binaries from that recorded metadata at the end of an install, and uses this metadata for reinstalls of the same package. In both of these cases the validation applied during dependency resolution is skipped. This situation is only reachable when your vendor directory is not populated from the same install run, which performs validation. For example a vendor directory restored from a shared or untrusted CI cache, copied in from an earlier container build stage, carried over from a Composer older than 2.10.2 or 2.2.29, or writable by a lower trust build step, could contain such malicious data.
The most realistic way to get hit is a composer install in a build or deploy step that reuses a vendor directory produced elsewhere, since the permission change is applied silently and with the privileges of the user running Composer.
Patched versions
Composer now verifies that each declared binary resolves to a path inside the installing package's own directory before it touches the file, and skips any binary that resolves outside it with a warning. Update to the patched releases (2.10.3 and 2.2.30).
Workarounds
Upgrading is the only complete fix.
Other sources
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.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
composer/composer/composerto a version that resolves this vulnerability.Fixed in 2.2.30 - Upgrade
Upgrade
composer/composer/composerto a version that resolves this vulnerability.Fixed in 2.10.3 - Upgrade
Upgrade
Composerto a version that resolves this vulnerability.Fixed in 2.10.3 - Upgrade
Upgrade
Composerto a version that resolves this vulnerability.Fixed in 2.2.30
Event History
Frequently Asked Questions
Which Composer installations are in scope?
The affected ranges are Composer 1.0 through 2.2.30 and Composer 2.3.0 through 2.10.3. Exposure depends on processing a malicious or compromised dependency, or on using attacker-influenced installed metadata under the described conditions.
What does an attacker need to control to use either attack path?
A dependency can include a binary symlink that resolves outside its installation directory. Alternatively, an attacker needs influence over vendor/composer/installed.json and a reinstall or regeneration of missing vendor/bin entries when the vendor directory was not populated by the same validated install run.
Which build and cache practices make the installed-metadata path relevant?
This path is reachable when vendor is restored from an untrusted cache, copied from an earlier build stage, retained from an older Composer run, or writable by a lower-trust build step. A vendor directory produced by the same validated install run does not meet that stated prerequisite.
What is the resulting impact on files outside the package directory?
Composer can follow the escaping path, make the external target world-readable and executable, and create a runnable vendor/bin proxy to it. The issue does not itself directly read or transmit data.