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Fencer Vulns
critical 9.8

CVE-2021-26707 json

Prototype pollution in Merge-deep

published 2021-06-02 5 y ago modified 2026-06-17 4 mo ago also GHSA-r6rj-9ch6-g264 , EUVD-2021-1394

cvss
9.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.9%
EPSS 1.9% chance of exploitation in 30 days, percentile 80%
public exploits
0
none known

Summary

The merge-deep library before 3.0.3 for Node.js can be tricked into overwriting properties of Object.prototype or adding new properties to it. These properties are then inherited by every object in the program, thus facilitating prototype-pollution attacks against applications using this library.

Patch / fix

  • npm merge-deep 3.0.3
  • merge-deep_project merge-deep 3.0.3

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-26707 updated cvss 9.8

nodejs-merge-deep: Prototype pollution of Object.prototype via a constructor payload

  • Red Hat OpenShift Service Mesh 1 servicemesh-prometheus
    affected: no fix planned “Out of support scope”
  • Red Hat OpenShift Container Platform 4 openshift4/ose-prometheus
    affected: no fix available “Fix deferred”
  • Red Hat OpenShift Service Mesh 2.0 servicemesh-prometheus Red Hat OpenShift Container Platform 4 openshift4/ose-thanos-rhel8
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.92% chance of exploitation in the next 30 days, higher than 80% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P
GitHub 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
npm merge-deep
<3.0.3
3.0.3

Classification

Weakness
  • CWE-1321 Improperly Controlled Modification of Object Prototype Attributes

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.