CVE-2021-20330

Specific replication command with malformed oplog entries can crash secondaries

MEDIUM

6.5

CVSS Score

Published: December 15, 2021 at 12:30 PM UTC

Updated: June 17, 2026 at 03:33 AM UTC

1 product affected across 1 vendorMongoDB

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Severity

MEDIUM6.5

Exploit prediction

EPSS 1%

SSVC

No known exploit

Description

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

MongoDB · MongoDB

95%

4.0 ≤ v < 4.0.274.0.0 ≤ v < 4.0.254.2 ≤ v < 4.2.164.2 ≤ v < 4.2.184.2.0 ≤ v < 4.2.144.4 ≤ v < 4.4.94.4.0 ≤ v < 4.4.64.0 4.2 4.4

Affected range stops below 4.0.25, so it looks safe — our inference, not a vendor statement

Affected range stops below 4.0.27, so it looks safe — our inference, not a vendor statement

Affected range stops below 4.2.14, so it looks safe — our inference, not a vendor statement

Affected range stops below 4.2.16, so it looks safe — our inference, not a vendor statement

Affected range stops below 4.2.18, so it looks safe — our inference, not a vendor statement

Affected range stops below 4.4.6, so it looks safe — our inference, not a vendor statement

Affected range stops below 4.4.9, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

https://jira.mongodb.org/browse/SERVER-36263

References (1)

x_refsource_MISCIssue TrackingPatchVendor Advisory

Source: [email protected]

https://jira.mongodb.org/browse/SERVER-36263

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

6.5MEDIUMmongodb

Attack Vector: NETWORK
Complexity: LOW
Privileges: LOW
User Interaction: NONE
Scope: UNCHANGED
Confidentiality: NONE
Integrity: NONE
Availability: HIGH

Vector?

Quick Info

StatusMODIFIED

CWE

CWE-20

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