Your RSA-2048 keys break in 2030. Find every one of them before attackers do.
📦
📦 npm
Not in CISA KEV
CRITICAL severity

CVE-2021-25953 — putil-merge

CRITICAL

CVE-2021-25953 is a critical-severity (CVSS 9.8) CWE-1321 vulnerability in putil-merge. 1 public exploit reference exists, so weaponization risk is real. A fix is available for putil-merge — see the affected versions and patch details below.

Prototype Pollution in putil-merge

Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
1 known
Exploitation data as of Oct 6, 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-2021-25953 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,386 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.

19other npm packages depend on this — each one inherits the vulnerability until it's patched upstream
putil-mergenpm
19Kdownloads / week

Description

Prototype pollution vulnerability in 'putil-merge' versions1.0.0 through 3.6.6 allows attacker to cause a denial of service and may lead to remote code execution.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
📦npmputil-merge≥ 1.0.0&&< 3.7.03.7.0npm install putil-merge@3.7.0

Affected Products

1 product · 1 configurations
Application
putil-mergeputil-merge_project
≥ 1.0.0 && ≤ 3.6.6
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 'putil-merge' versions1.0.0 through…

whitesourcesoftware.comNVDJul 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 putil-merge, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update putil-merge to 3.7.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-25953 is resolved across your whole dependency graph.

  3. 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

Prototype pollution vulnerability in 'putil-merge' versions1.0.0 through 3.6.6 allows attacker to cause a denial of service and may lead to remote code execution.
O3 Security · Impact-Aware SCA

Is CVE-2021-25953 in your dependencies?

Find it across npm, including transitive dependencies.

Scan my dependencies How O3 SCA works
CVE-2021-25953: putil-merge RCE — Fixed in 3.7.0