# CVE-2026-120820: MongoDB Server memory exhaustion in FLE2 operation statistics

Source: https://junglewise.ai/threats/cve-2026-120820-mongodb-server-maintains-an-in-memory-table-of-per-namespace  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-10. Updated: 2026-11-10  
License: CC BY 4.0 with a link back

CVE-2026-120820 · Severity: medium · CVSS 4.3 · Published 2026-11-10

MongoDB Server, a widely-used NoSQL database, maintains in-memory statistics tables for encrypted-field operations that can grow without bound when a user makes ordinary database read/write requests using arbitrary namespace names. An attacker with basic database read privileges can force the server to consume steadily increasing amounts of memory by issuing repeated commands, degrading performance and requiring a server restart to reclaim memory.

Technologies: [MongoDB Server](https://junglewise.ai/threats/technologies/mongodb-server). Vendors: [MongoDB](https://junglewise.ai/threats/vendors/mongodb).

## Quick answers

**Is CVE-2026-120820 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-120820 being exploited in the wild.

**How severe is CVE-2026-120820?** Medium severity, with a CVSS score of 4.3, published 10 November 2026.

**Which products and versions are affected?** MongoDB Server before 8.0.37, 8.3.16, 9.0.7.

**Is there a fix for CVE-2026-120820?** Yes: fixed in 8.0.37, 8.3.16, 9.0.7. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-120820 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-120820?** Check whether you run MongoDB Server at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in 8.0.37, 8.3.16, 9.0.7

## Technical details

The vulnerability exists in fle_stats.cpp where the registerCollectionStats() function creates map entries for any namespace in a request without limiting the number of entries or providing removal mechanisms. The entries are created before transaction validation, so entries persist even if operations fail. On mongos nodes, entries are never removed because there is no local collection catalog. An authenticated user with find, insert, update, or delete privileges can exploit this by sending QE-shaped commands against non-existent or unencrypted collections with arbitrary namespace names, each creating a permanent memory allocation.

## Affected products

- MongoDB Server before 8.0.37, 8.3.16, 9.0.7

## Timeline

- 2026-11-10: disclosed
- 2026-11-10: patched

## References

- [https://jira.mongodb.org/browse/SERVER-135737](https://jira.mongodb.org/browse/SERVER-135737)

## Related threats

- [MongoDB Server authorization bypass in aggregation pipeline](https://junglewise.ai/threats/cve-2026-120825-an-authorization-weakness-in-the-aggregation-framework-of)
- [MongoDB Server use-after-free in time-series bucket validation](https://junglewise.ai/threats/cve-2026-120824-a-use-after-free-in-the-time-series-collection-component-of)
- [MongoDB Server missing authorization check in aggregation framework](https://junglewise.ai/threats/cve-2026-120823-a-missing-authorization-check-in-the-aggregation-framework-of)
- [MongoDB Server authorization bypass in applyOps](https://junglewise.ai/threats/cve-2026-120822-mongodb-server-may-omit-an-authorization-check-on-the-resource)
- [MongoDB Server use-after-free in aggregation framework](https://junglewise.ai/threats/cve-2026-120821-a-use-after-free-in-the-aggregation-framework-of-mongodb-server)