CVE-2021-33587 is a high-severity (CVSS 7.5) vulnerability in css-what. A fix is available for css-what — see the affected versions and patch details below.
Denial of service in css-what
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
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
css-whatnpmDescription
The css-what package 4.0.0 through 5.0.0 for Node.js does not ensure that attribute parsing has Linear Time Complexity relative to the size of the input.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | css-what | ≥ 4.0.0&&< 5.0.1 | 5.0.1npm install css-what@5.0.1 |
Affected Products
css-whatcss-what_projecte-series performance analyzernetappDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for css-what, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update css-what to 5.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-33587 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.
Frequently Asked Questions
Is CVE-2021-33587 in your dependencies?
Find it across npm, including transitive dependencies.