# CVE-2026-84971: libmongocrypt: Improper handling of an unexpected value size in the decryption path of a client-side encryption library can cause a...

CVE-2026-84971 is fixed in libmongocrypt on 1 platform by DEBIAN-CVE-2026-84971 (version 1.20.4-1), released September 10, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-84971
- Priority: Routine
- CVSS: n/a
- EPSS: 0.0026
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 3, 2026

## Description

Improper handling of an unexpected value size in the decryption path of a client-side encryption library can cause a failed internal check that terminates the process using the library. A party able to place a suitably formed encrypted value where an application will decrypt it, or able to control the responses the application receives, may cause that application to stop running.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libmongocrypt Debian 14 | 1.20.4-1 | [DEBIAN-CVE-2026-84971](https://patchblox.com/security/data/fix/linux/debian-cve-2026-84971.md) | Sep 10, 2026 |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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