CVE-2026-46420

A command injection vulnerability was identified in shivammathur/setup-php when the action resolves the PHP version from repository-controlled files and uses that value while generating the platform setup script.

In affected versions, setup-php may read the PHP version from:

• .php-version
• composer.lock via platform-overrides.php
• composer.json via config.platform.php

If an attacker can influence one of these files and the workflow executes setup-php in a trusted context, they may be able to execute commands on the GitHub Actions runner.

Technical details

In affected versions, repository-derived PHP version values were insufficiently constrained before being incorporated into the generated shell or PowerShell setup script executed by the action. This could allow attacker-controlled values from supported repository files to influence script execution in trusted workflow contexts.

This issue is exploitable when setup-php is run after checking out attacker-controlled repository contents and resolves the PHP version from repository files.

The most significant example is a privileged workflow such as pull_request_target that checks out untrusted pull request code before invoking setup-php. Similar risk can also arise in other workflows that operate on attacker-controlled refs, branches, or repository contents in a trusted context.

This is not a separate security boundary when an attacker can already modify the workflow definition itself or directly control the php-version workflow input, since that level of access already permits arbitrary command execution in GitHub Actions.

Untrusted input reaches a shell command, allowing arbitrary commands to run on the host. Typical impact: code execution in the application's environment.

CVE-2026-46420 has a CVSS score of 5.6 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.37.1); upgrading removes the vulnerable code path.

Kodem intelligence

If you are using shivammathur/setup-php@v2, no action is needed on your end. Users who pin the setup-php release version or release version SHA should upgrade to a patched version.

The fix validates PHP version inputs, constrains manifest-derived versions, hardens script generation at the execution, and includes additional checks in related input-handling paths.

1. What is CVE-2026-46420? CVE-2026-46420 is a medium-severity OS command injection vulnerability in shivammathur/setup-php (actions), affecting versions >= 2.25.0, < 2.37.1. It is fixed in 2.37.1. Untrusted input reaches a shell command, allowing arbitrary commands to run on the host.
2. How severe is CVE-2026-46420? CVE-2026-46420 has a CVSS score of 5.6 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of shivammathur/setup-php are affected by CVE-2026-46420? shivammathur/setup-php (actions) versions >= 2.25.0, < 2.37.1 is affected.
4. Is there a fix for CVE-2026-46420? Yes. CVE-2026-46420 is fixed in 2.37.1. Upgrade to this version or later.
5. Is CVE-2026-46420 exploitable, and should I be worried? Whether CVE-2026-46420 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-46420 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-46420? Upgrade shivammathur/setup-php to 2.37.1 or later.