CVE-2021-43307 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.
Regular expression denial of service in semver-regex
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
An exponential ReDoS (Regular Expression Denial of Service) can be triggered in the semver-regex npm package, when an attacker is able to supply arbitrary input to the test() method
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | semver-regex | all versions | 3.1.4npm install semver-regex@3.1.4 |
| 📦npm | semver-regex | ≥ 4.0.0&&< 4.0.3 | 4.0.3npm install semver-regex@4.0.3 |
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 3.1.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-43307 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Frequently Asked Questions
Is CVE-2021-43307 in your dependencies?
Find it across npm, including transitive dependencies.