RCE in Shivammathur Setup-Php

CVE-2026-46420

setup-php is a GitHub action to set up PHP with extensions, php.ini configuration, coverage drivers, and tools. From 2.25.0 prior to 2.37.1, shivammathur/setup-php resolves the PHP version from repository-controlled files such as .php-version, composer.lock through platform-overrides.php, and composer.json through config.platform.php, and insufficiently constrains those values before incorporating them into generated shell or PowerShell setup scripts, allowing command injection on a GitHub Actions runner when workflows such as pull_request_target check out attacker-controlled contents before invoking setup-php. This issue is fixed in version 2.37.1.

Vulnerability class: Command Injection (OS Command Injection)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 5.6 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L.

EPSS exploit prediction

EPSS: 0.020 (80.5th percentile), scored .

Low probability of exploitation in the next 30 days, but still tracked. 80th percentile — 80.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-46420: held from 0.015 to 0.020.

EPSS over last 30 days · oldest: 0.015 · newest: 0.020 · change: +0.005

Affected products

Weakness classification (CWE)

Public proof-of-concept exploits

References

Frequently asked questions

What is CVE-2026-46420?
CVE-2026-46420 is a medium-severity vulnerability in Shivammathur Setup-Php, classified under OS Command Injection. CVSS score: 5.6/10. Published 2026-07-17.
How severe is CVE-2026-46420?
Medium severity. CVSS v3 base score is 5.6 out of 10.
Is CVE-2026-46420 known to be exploited?
1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.