---
id: CVE-2026-84971
title: >-
  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
summary: >-
  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 v…
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-617
vendor: mongodb
product: libmongocrypt
affected:
  - 'libmongocrypt >= 1.7.0, < 1.20.4'
patched:
  - libmongocrypt 1.20.4
published: '2026-09-03'
updated: '2026-09-17'
sourceUpdated: '2026-09-17T13:59:13.180'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-84971'
references:
  - url: 'https://jira.mongodb.org/browse/MONGOCRYPT-971'
    label: cna@mongodb.com
tags:
  - nvd
epss: 0.00259
epssPercentile: 0.15649
ingestedAt: '2026-09-17T14:19:30.938Z'
---

## Overview

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.

## Affected

- `libmongocrypt >= 1.7.0, < 1.20.4`

## Remediation

Upgrade past the affected range:

- `libmongocrypt 1.20.4`