CVE-2021-20330 Specific replication command with malformed oplog entries can crash secondaries

What is CVE-2021-20330?

CVE-2021-20330 is a medium-severity denial of service vulnerability in Mongodb Mongodb, published on 15 Dec 2021. Any signed-in user can exploit it over the network, with no action from the victim.

Official 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.

Weakness: CWE-20

Which versions are affected by CVE-2021-20330?

1 open source package ship an affected version, including mongodb. It affects 1 product.

Products include Mongodb Mongodb.

How do I fix CVE-2021-20330?

Upgrade mongodb to a fixed version for your release line: 4.0.25, 4.2.14 or 4.4.6.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2021-20330 being exploited?

There is no known exploitation of CVE-2021-20330 in the wild and no public exploit code.

Other vulnerabilities in Mongodb Mongodb

• CVE-2025-14847 MongoDB and MongoDB Server Improper Handling of Length Parameter Inconsistency Exploited High 8.7
• CVE-2026-82067 Auth bypass in MongoDB Server Critical 9.2
• CVE-2026-13072 MongoDB Improper Input Validation in Compute Mode External Data Processing Leading to Memory Corruption Critical 9.2
• CVE-2017-15535 Denial of service in n/a Critical 9.1
• CVE-2026-18691 Improper Authentication in MongoDB Intra-Cluster Connections Allows Credential Exposure Critical 9.0

All Mongodb Mongodb vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BIT-mongodb-2021-20330, GHSA-8jvf-jqg4-r6h2.