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

Published · last modified .

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.

EPSS exploit prediction

EPSS: 0.004 (35.6th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 36th percentile — 35.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-16266: held from 0.004 to 0.004.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000

Affected products

  • Mongo-Object — versions 0

Weakness classification (CWE)

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.