How severe is CVE-2021-43138?

CVE-2021-43138 has a CVSS score of 7.8/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-43138?

CVE-2021-43138 affects the following packages: async (npm), async (npm). Ecosystems affected: npm.

How do I fix CVE-2021-43138?

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.

How do I detect CVE-2021-43138 in my npm dependencies?

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.

How do I mitigate CVE-2021-43138 if there is no patch (or I can't update yet)?

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.

Is CVE-2021-43138 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-43138, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-43138?

CVE-2021-43138 has an EPSS (Exploit Prediction Scoring System) score of 3.3%, placing it in the 89th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-43138?

CVE-2021-43138 is classified as CWE-1321 (CWE-1321). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-43138 published, and has it been updated?

CVE-2021-43138 was published on April 6, 2022 and was last updated on October 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

HIGH severity

CVE-2021-43138 — async

HIGHFix: caolan/async@e1ecdbf

CVE-2021-43138 is a high-severity (CVSS 7.8) CWE-1321 vulnerability in async. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for async — see the affected versions and patch details below.

Prototype Pollution in async

Also known asGHSA-fwr7-v2mv-hh25

Published

Apr 6, 2022

Updated

Oct 20, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

1 known

Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

3.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs89th percentile — riskier than 89% of all scored CVEsHighest risk

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

2 pkgs affected

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.

34Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

asyncnpm

143.5Mdownloads / week

Description

A vulnerability exists in Async through 3.2.1 for 3.x and through 2.6.3 for 2.x (fixed in 3.2.2 and 2.6.4), which could let a malicious user obtain privileges via the mapValues() method.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`async`	≥ 3.0.0&&< 3.2.2	3.2.2`npm install async@3.2.2`
📦npm	`async`	≥ 2.0.0&&< 2.6.4	2.6.4`npm install async@2.6.4`

Affected Products

2 products · 4 configurations

Application

asyncasync_project

≥ 3.0.0 && < 3.2.2

range

fedorafedoraproject

2 versions

3637

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

In Async before 2.6.4 and 3.x before 3.2.2, a malicious user can obtain …

jsfiddle.netNVDApr 2022

Detection & mitigation playbook

Open-source dependency

Detect
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.

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.

Red HatModerate

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

A vulnerability exists in Async through 3.2.1 for 3.x and through 2.6.3 for 2.x (fixed in 3.2.2 and 2.6.4), which could let a malicious user obtain privileges via the `mapValues()` method.

O3 Security · Impact-Aware SCA

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