What is CVE-2021-20330?

CVE-2021-20330 is a medium-severity vulnerability in MongoDB, classified under Improper Input Validation. CVSS score: 6.5/10. Published 2021-12-15.

How severe is CVE-2021-20330?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Improper input validation in MongoDB

CVE-2021-20330

An attacker with basic CRUD permissions on a replicated collection can run the applyOps command with specially malformed oplog entries, resulting in a potential denial of service on secondaries. This issue affects MongoDB Server v4.0 versions prior to 4.0.27; MongoDB Server v4.2 versions prior to 4.2.16; MongoDB Server v4.4 versions prior to 4.4.9.

Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)

Published 2021-12-15 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.010 (62.9th percentile), scored 2026-10-03.

Low probability of exploitation in the next 30 days, but still tracked. 63rd percentile — 62.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.010 · newest: 0.010 · change: +0.000

Affected products

MongoDB
MongoDB Inc. Server — versions 4.0, 4.2, 4.4

Weakness classification (CWE)

CWE-20 — Improper Input Validation

References

jira.mongodb.org/browse/SERVER-36263 (Patch, Issue Tracking, Vendor Advisory)

Frequently asked questions

What is CVE-2021-20330?: CVE-2021-20330 is a medium-severity vulnerability in MongoDB, classified under Improper Input Validation. CVSS score: 6.5/10. Published 2021-12-15.
How severe is CVE-2021-20330?: Medium severity. CVSS v3 base score is 6.5 out of 10.