CVE-2021-43138 is a high-severity (CVSS 7.8) CWE-1321 vulnerability in async. 1 public exploit reference exists, so weaponization risk is real. A fix is available for async — see the affected versions and patch details below.
Prototype Pollution in async
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2021-43138 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,333 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
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.
asyncnpmDescription
In Async before 2.6.4 and 3.x before 3.2.2, a malicious user can obtain privileges via the mapValues() method, aka lib/internal/iterator.js createObjectIterator prototype pollution.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | async | ≥ 3.0.0&&< 3.2.2 | 3.2.2npm install async@3.2.2 |
| 📦npm | async | ≥ 2.0.0&&< 2.6.4 | 2.6.4npm install async@2.6.4 |
Research 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 async, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update async to 3.2.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-43138 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.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2021-43138 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-43138. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
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.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Migration Toolkit for Containers 1.7 | rhmtc/openshift-migration-ui-rhel8:v1.7.7-3 | RHSA-2023:0693 |
| Red Hat OpenShift Service Mesh 2.2 for RHEL 8 | openshift-service-mesh/prometheus-rhel8:2.2.7-7 | RHSA-2023:3645 |
Frequently Asked Questions
Is CVE-2021-43138 in your dependencies?
O3 Security finds CVE-2021-43138 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.