CVE-2026-46420 is a medium-severity (CVSS 5.6) OS Command Injection vulnerability in shivammathur/setup-php. A fix is available for shivammathur/setup-php — see the affected versions and patch details below.
setup-php: Command Injection in Repository-Derived PHP Version Resolution
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-46420.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-46420 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 381,682 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
shivammathur/setup-phpReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects GitHub Actions packages — download data is not available via public APIs for these ecosystems.
Description
Summary
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-versioncomposer.lockviaplatform-overrides.phpcomposer.jsonviaconfig.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.
Impact
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.
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.
Remediation
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦GitHub Actions | shivammathur/setup-php | ≥ 2.25.0&&< 2.37.1 | 2.37.1 |
Affected Products
setup phpshivammathurDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for shivammathur/setup-php, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update shivammathur/setup-php to 2.37.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-46420 is resolved across your whole dependency graph.
Workarounds
Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.
Frequently Asked Questions
Is CVE-2026-46420 in your dependencies?
Find it across GitHub Actions, including transitive dependencies.