dbcve.org
MongoDBDatabase / datastore

CVE-2021-20330

MEDIUM · 6.5 CVSS v3.1 Published 2021-12-15
Fix available
A fix is available. Upgrade to 4.0.25 / 4.2.14 or later.
See remediation →
71/100
Remediation priority · Elevated
Remotely reachable Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-20

The application accepts input without confirming it is well-formed or within expected bounds, so malformed data can push the program into states its author never anticipated. Attackers probe these gaps to trigger crashes, bypass logic, or feed tainted values into more dangerous operations downstream. Remediating it well means validating and normalising every input at the boundary against a strict allow-list — not merely filtering known-bad values.

General guidance for the improper input validation class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
MongoDBDatabase / datastore
Affected:>= 4.0.0, < 4.0.25>= 4.2.0, < 4.2.14>= 4.4.0, < 4.4.6

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 4.0.25 / 4.2.14 / 4.4.6 or later
Fixed in 4.0.254.2.144.4.6
Vendor patch jira.mongodb.org →
Recommended fix High confidence

MongoDB 4.0.27+ (if on 4.0.x), 4.2.16+ (if on 4.2.x), or 4.4.9+ (if on 4.4.x)

  1. 1. Identify the currently installed MongoDB Server version using: db.version() in the mongo shell or mongod --version from command line
  2. 2. Based on your current major version line, plan upgrade path: If on 4.0.x, upgrade to 4.0.27 or later; If on 4.2.x, upgrade to 4.2.16 or later; If on 4.4.x, upgrade to 4.4.9 or later
  3. 3. Review MongoDB upgrade documentation at https://docs.mongodb.com/manual/release-notes/ for your specific upgrade path
  4. 4. Before upgrading, take a backup of all databases
  5. 5. Stop all MongoDB services (mongod, mongos) on all replica set members
  6. 6. Install the new MongoDB Server version (4.0.27+/4.2.16+/4.4.9+) using your package manager or direct download from https://www.mongodb.com/download-center/community
  7. 7. Start mongod on secondary members first, then primary (for replica sets)
  8. 8. Verify the upgrade by checking: db.version() returns the expected version
Caveat Major version upgrades (e.g., 4.0 to 4.2) may require careful planning and could have feature compatibility changes; review MongoDB's compatibility notes before upgrading across major versions

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,600. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-20330 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data