CVE-2020-13756 is a critical-severity (CVSS 9.8) Code Injection vulnerability in sabberworm/php-css-parser. 3 public exploit or proof-of-concept references are indexed, so weaponization risk is real. A fix is available for sabberworm/php-css-parser — see the affected versions and patch details below.
Sabberworm PHP CSS Parser Code injection vulnerability in allSelectors()
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
sabberworm/php-css-parser🐘sabberworm/php-css-parser🐘sabberworm/php-css-parser🐘sabberworm/php-css-parser🐘sabberworm/php-css-parser🐘sabberworm/php-css-parser🐘sabberworm/php-css-parser🐘sabberworm/php-css-parser+5 moreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
Sabberworm PHP CSS Parser before 8.3.1 calls eval on uncontrolled data, possibly leading to remote code execution if the function allSelectors() or getSelectorsBySpecificity() is called with input from an attacker.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | sabberworm/php-css-parser | ≥ 8.3.0&&< 8.3.1 | 8.3.1composer require sabberworm/php-css-parser:^8.3.1 |
| 🐘Packagist | sabberworm/php-css-parser | ≥ 8.2.0&&< 8.2.1 | 8.2.1composer require sabberworm/php-css-parser:^8.2.1 |
| 🐘Packagist | sabberworm/php-css-parser | ≥ 8.1.0&&< 8.1.1 | 8.1.1composer require sabberworm/php-css-parser:^8.1.1 |
| 🐘Packagist | sabberworm/php-css-parser | ≥ 8.0.0&&< 8.0.1 | 8.0.1composer require sabberworm/php-css-parser:^8.0.1 |
| 🐘Packagist | sabberworm/php-css-parser | ≥ 7.0.0&&< 7.0.4 | 7.0.4composer require sabberworm/php-css-parser:^7.0.4 |
| 🐘Packagist | sabberworm/php-css-parser | ≥ 6.0.0&&< 6.0.2 | 6.0.2composer require sabberworm/php-css-parser:^6.0.2 |
Affected Products
php css parsersabberwormResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for sabberworm/php-css-parser, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update sabberworm/php-css-parser to 8.3.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-13756 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.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Frequently Asked Questions
Is CVE-2020-13756 in your dependencies?
Find it across Packagist, including transitive dependencies.