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Not in CISA KEV
HIGH severity

CVE-2018-3722 — merge-deep

HIGHFix: jonschlinkert/merge-deep@2c33634

CVE-2018-3722 is a high-severity (CVSS 8.8) CWE-471 vulnerability in merge-deep. 1 public exploit reference exists, so weaponization risk is real. A fix is available for merge-deep — see the affected versions and patch details below.

Prototype Pollution in merge-deep

Also known asGHSA-9g9w-hmvj-5h57
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
1 known
Exploitation data as of Oct 11, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
2.0%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs81th percentile — riskier than 81% of all scored CVEsHighest risk
0.00%0.85%1.69%2.54%0.5%2.0%Apr 26Aug 26Oct 26

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

How urgent is this, really

CVE-2018-3722 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 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.

330other npm packages depend on this — each one inherits the vulnerability until it's patched upstream
merge-deepnpm
2.0Mdownloads / week

Description

merge-deep node module before 3.0.1 suffers from a Modification of Assumed-Immutable Data (MAID) vulnerability, which allows a malicious user to modify the prototype of "Object" via proto, causing the addition or modification of an existing property that will exist on all objects.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
📦npmmerge-deepall versions3.0.1npm install merge-deep@3.0.1

Affected Products

1 product · 1 configurations
Application
merge-deepmerge-deep_project
< 3.0.1
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.

merge-deep node module before 3.0.1 suffers from a Modification of Assum…

hackerone.comNVDOct 2019

Detection & mitigation playbook

Open-source dependency

  1. Detect

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

  2. Fix

    Update merge-deep to 3.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2018-3722 is resolved across your whole dependency graph.

  3. 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.

Frequently Asked Questions

merge-deep node module before 3.0.1 suffers from a Modification of Assumed-Immutable Data (MAID) vulnerability, which allows a malicious user to modify the prototype of "Object" via __proto__, causing the addition or modification of an existing property that will exist on all objects.
O3 Security · Impact-Aware SCA

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CVE-2018-3722: merge-deep — Fixed in 3.0.1