CVE-2021-23364 is a medium-severity (CVSS 5.3) CWE-1333 vulnerability in browserslist. 2 public exploit references exist, so weaponization risk is real. A fix is available for browserslist — see the affected versions and patch details below.
Regular Expression Denial of Service in browserslist
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-23364 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
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.
browserslistnpmDescription
The package browserslist from 4.0.0 and before 4.16.5 are vulnerable to Regular Expression Denial of Service (ReDoS) during parsing of queries.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | browserslist | ≥ 4.0.0&&< 4.16.5 | 4.16.5npm install browserslist@4.16.5 |
Affected Products
browserslistbrowserslist_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 browserslist, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update browserslist to 4.16.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23364 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.
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.
While some components do package a vulnerable version of nodejs browserslist library, access to them requires OpenShift OAuth credentials and hence have been marked with a Low impact. This applies to the following products: - OpenShift Container Platform (OCP) - OpenShift ServiceMesh (OSSM) - Red Hat Advanced Cluster…
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Quay 3 | quay/quay-rhel8:v3.6.0-62 | RHSA-2021:3917 |
Frequently Asked Questions
Is CVE-2021-23364 in your dependencies?
Find it across npm, including transitive dependencies.