What is CVE-2026-16266?

CVE-2026-16266 is a medium-severity vulnerability in Mongo-Object, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 4.0/10. Published 2026-07-21.

How severe is CVE-2026-16266?

Medium severity. CVSS v3 base score is 4.0 out of 10.

Prototype Pollution in Mongo-Object

CVE-2026-16266

Versions of the package mongo-object before 3.0.3 are vulnerable to Prototype Pollution via the expandKey() function in util.js. An attacker can modify the JavaScript prototype chain by supplying a crafted property path containing special keys such as __proto__.

Vulnerability class: Prototype Pollution

EPSS: 0.004 (35.5th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 4.0 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N.

Affected products

N/a Mongo-object — versions 0

Weakness classification (CWE)

CWE-1321 — Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution)

References

Frequently asked questions

What is CVE-2026-16266?: CVE-2026-16266 is a medium-severity vulnerability in Mongo-Object, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 4.0/10. Published 2026-07-21.
How severe is CVE-2026-16266?: Medium severity. CVSS v3 base score is 4.0 out of 10.