CVE-2021-41167 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in modern-async. 1 public exploit reference exists, so weaponization risk is real. A fix is available for modern-async — see the affected versions and patch details below.
modern-async's `forEachSeries` and `forEachLimit` functions do not limit the number of requests
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-41167 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.
modern-asyncnpmDescription
modern-async is an open source JavaScript tooling library for asynchronous operations using async/await and promises. In affected versions a bug affecting two of the functions in this library: forEachSeries and forEachLimit. They should limit the concurrency of some actions but, in practice, they don't. Any code calling these functions will be written thinking they would limit the concurrency but they won't. This could lead to potential security issues in other projects. The problem has been patched in 1.0.4. There is no workaround.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | modern-async | all versions | 1.0.4npm install modern-async@1.0.4 |
Affected Products
modern-asyncmodern-async_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 modern-async, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update modern-async to 1.0.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-41167 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-2021-41167 in your dependencies?
Find it across npm, including transitive dependencies.