What is CVE-2021-3766?

CVE-2021-3766 is a critical-severity vulnerability in Objection Project, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 9.8/10. Published 2021-09-06.

How severe is CVE-2021-3766?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Prototype Pollution in Objection Project

CVE-2021-3766

objection.js is vulnerable to Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

Vulnerability class: Prototype Pollution

Published 2021-09-06 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.015 (73.6th percentile), scored 2026-10-24.

Low probability of exploitation in the next 30 days, but still tracked. 74th percentile — 73.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.015 · newest: 0.015 · change: 0.000

Affected products

Objection Project
Vincit Vincit/objection.js — versions unspecified

Weakness classification (CWE)

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

References

huntr.dev/bounties/c98e0f0e-ebf2-4072-be73-a1848ea031cc (Exploit, Patch, Third Party Advisory, Issue Tracking)
github.com/Vincit/objection.js/commit/46b842a6bc897198b83f41ac85c92864b991d7e9 (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-3766?: CVE-2021-3766 is a critical-severity vulnerability in Objection Project, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 9.8/10. Published 2021-09-06.
How severe is CVE-2021-3766?: Critical severity. CVSS v3 base score is 9.8 out of 10.