CVE-2020-13756 is a critical-severity (CVSS 9.8) Code Injection vulnerability in sabberworm/php-css-parser. 3 public exploit references exist, 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
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2020-13756 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE sits: patch-first territory.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the 10–50% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
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 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Sabberworm PHP CSS Parser before 8.3.1 calls eval on uncontrolled data, …
Sabberworm PHP CSS Parser before 8.3.1 calls eval on uncontrolled data, …
Sabberworm PHP CSS Parser before 8.3.1 calls eval on uncontrolled data, …
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
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2020-13756 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2020-13756. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
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?
O3 Security finds CVE-2020-13756 across Packagist dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.