What is CVE-2021-3645?

CVE-2021-3645 is a critical-severity vulnerability in Merge Project, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 9.8/10. Published 2021-09-10.

How severe is CVE-2021-3645?

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

Prototype Pollution in Merge Project

CVE-2021-3645

merge is vulnerable to Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

Vulnerability class: Prototype Pollution

Published 2021-09-10 · 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: 0.014 (72.0th percentile), scored 2026-09-30.

Low probability of exploitation in the next 30 days, but still tracked. 72nd percentile — 72.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.014 · newest: 0.014 · change: 0.000

Affected products

Merge Project
Viking04 Viking04/merge — versions unspecified

Weakness classification (CWE)

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

References

huntr.dev/bounties/ef387a9e-ca3c-4c21-80e3-d34a6a896262 (Exploit, Third Party Advisory)
github.com/viking04/merge/commit/baba40332080b38b33840d2614df6d4142dedaf6 (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-3645?: CVE-2021-3645 is a critical-severity vulnerability in Merge Project, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 9.8/10. Published 2021-09-10.
How severe is CVE-2021-3645?: Critical severity. CVSS v3 base score is 9.8 out of 10.