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MEDIUM severity

CVE-2021-23561 — comb

MEDIUM

CVE-2021-23561 is a medium-severity (CVSS 6.5) CWE-1321 vulnerability in comb. 1 public exploit reference exists, so weaponization risk is real. No vendor fix is recorded yet; mitigation options are listed below.

Prototype Pollution in comb

Published
Updated
Affected
1 pkg
Patched
See advisory
Exploits
1 known
Exploitation data as of Oct 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.2%probability of exploitation in next 30 days
Lower Risk+0.04%
Lower risk than most CVEs68th percentile — riskier than 68% of all scored CVEsHighest risk
0.00%0.57%1.14%1.71%0.5%1.2%Apr 26Aug 26Oct 26

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

How urgent is this, really

CVE-2021-23561 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.

12other npm packages depend on this — each one inherits the vulnerability until it's patched upstream
combnpm
2Kdownloads / week

Description

All versions of package comb are vulnerable to Prototype Pollution via the deepMerge() function.

Affected Packages

1 total
EcosystemPackageVulnerable rangeFix
📦npmcomball versionsNo fix

Affected Products

1 product · 1 configurations
Application
combc2fo
all
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.

All versions of package comb are vulnerable to Prototype Pollution via t…

snyk.ioNVDDec 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 comb, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Remediation status

    No patched version of comb has shipped for CVE-2021-23561 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

    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.

Frequently Asked Questions

All versions of package comb are vulnerable to Prototype Pollution via the `deepMerge()` function.
O3 Security · Impact-Aware SCA

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CVE-2021-23561: comb: Prototype Pollution