CVE-2021-3795 is a high-severity (CVSS 7.5) CWE-1333 vulnerability in semver-regex. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for semver-regex — see the affected versions and patch details below.
semver-regex Regular Expression Denial of Service (ReDOS)
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.
semver-regexnpmDescription
npm semver-regex is vulnerable to Inefficient Regular Expression Complexity
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | semver-regex | all versions | 3.1.3npm install semver-regex@3.1.3 |
| 📦npm | semver-regex | ≥ 4.0.0&&< 4.0.1 | 4.0.1npm install semver-regex@4.0.1 |
Affected Products
semver-regexsemver-regex_projectResearch 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 semver-regex, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update semver-regex to 3.1.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3795 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-2021-3795 in your dependencies?
Find it across npm, including transitive dependencies.