CVE-2021-20330Network attack vector

Secondary crashes via unvalidated applyOps oplog entries

Published Dec 15, 2021 · Updated Sep 16, 2024

Improper input validation in MongoDB Server 4.0, 4.2, and 4.4 allows remote authenticated users to crash replica-set secondaries. The applyOps command intentionally skips per-operation validation for oplog replay, but affected releases expose that path to users with basic collection CRUD rights. A replica set and authenticated collection access are required; malformed oplog entries crash secondary mongod processes and interrupt replication availability.

CVSS severity6.5
Medium
EPSS probability1.04%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in MongoDB Server 4.0, 4.2, and 4.4 allows remote authenticated users to crash replica-set secondaries. The applyOps command intentionally skips per-operation validation for oplog replay, but affected releases expose that path to users with basic collection CRUD rights. A replica set and authenticated collection access are required; malformed oplog entries crash secondary mongod processes and interrupt replication availability.

The record

CVE
CVE-2021-20330
Published
Dec 15, 2021
Updated
Sep 16, 2024
Vendor
MongoDB
Product
MongoDB Server
Classifications
CWE-20, T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 15, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4.0 <4.0.27
  2. Affected versionversion=4.2 <4.2.16
  3. Affected versionversion=4.2 <4.2.18
  4. Affected versionversion=4.4 <4.4.9

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

MongoDB · MongoDB Serverversion=4.0 <4.0.27; version=4.2 <4.2.16; version=4.2 <4.2.18; version=4.4 <4.4.9

Published CVSS scores

6.5MongoDB, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
4.0NVDAV:N/AC:L/Au:S/C:N/I:N/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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