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CVE-2021-25945 — js-extend

CRITICAL

CVE-2021-25945 is a critical-severity (CVSS 9.8) CWE-1321 vulnerability in js-extend. 1 public exploit reference exists, so weaponization risk is real. No vendor fix is recorded yet; mitigation options are listed below.

Prototype pollution vulnerability in js-extend

Published
Updated
Affected
1 pkg
Patched
See advisory
Exploits
1 known
Exploitation data as of Oct 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
3.0%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs87th percentile — riskier than 87% of all scored CVEsHighest risk
2.04%2.51%2.99%3.46%2.5%3.0%Apr 26Aug 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-25945 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,987 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg 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.

27other npm packages depend on this — each one inherits the vulnerability until it's patched upstream
js-extendnpm
10Kdownloads / week

Description

Prototype pollution vulnerability in 'js-extend' versions 0.0.1 through 1.0.1 allows attacker to cause a denial of service and may lead to remote code execution.

Affected Packages

1 total
EcosystemPackageVulnerable rangeFix
📦npmjs-extendall versionsNo fix

Affected Products

1 product · 1 configurations
Application
js-extendjs-extend_project
≥ 0.0.1 && ≤ 1.0.1
range
Exploits & PoCs
1

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

Prototype pollution vulnerability in 'js-extend' versions 0.0.1 through …

whitesourcesoftware.comNVDJun 2021

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for js-extend, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Remediation status

    No patched version of js-extend has shipped for CVE-2021-25945 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.

  3. Mitigate without a patch

    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

Prototype pollution vulnerability in 'js-extend' versions 0.0.1 through 1.0.1 allows attacker to cause a denial of service and may lead to remote code execution.
O3 Security · Impact-Aware SCA

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CVE-2021-25945: js-extend: Prototype pollution vulnerability