---
id: CVE-2026-19867
title: >-
  Uncapped mention keys in user notification properties allow CPU exhaustion
  during post processing
summary: >-
  Mattermost versions 11.10.x <= 11.10.0, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5,
  11.7.x <= 11.7.10 fail to cap the number and size of mention keys stored in a
  user's notification properties, and to bound the quadratic multibyte-keyword
  matchi…
severity: medium
cvss: 4.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L'
cvssSource: cna
cwe:
  - CWE-770
vendor: Mattermost
product: Mattermost
affected:
  - Mattermost >= 11.10.0 <= 11.10.0
  - Mattermost >= 11.9.0 <= 11.9.1
  - Mattermost >= 11.8.0 <= 11.8.5
  - Mattermost >= 11.7.0 <= 11.7.10
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-10-16T11:59:55.782423Z'
published: '2026-10-16'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T12:00:11.330Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-19867'
references:
  - url: 'https://mattermost.com/security-updates'
    label: MMSA-2026-00773
tags:
  - cve.org
ingestedAt: '2026-10-16T08:02:23.125Z'
---

## Overview

Mattermost versions 11.10.x <= 11.10.0, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10 fail to cap the number and size of mention keys stored in a user's notification properties, and to bound the quadratic multibyte-keyword matching performed for each post, which allows an authenticated user to degrade post-processing latency and consume excessive CPU on behalf of other members of any channel they share via storing an oversized notify_props.mention_keys list on their own profile.. Mattermost Advisory ID: MMSA-2026-00773

## Affected

- `Mattermost >= 11.10.0 <= 11.10.0`
- `Mattermost >= 11.9.0 <= 11.9.1`
- `Mattermost >= 11.8.0 <= 11.8.5`
- `Mattermost >= 11.7.0 <= 11.7.10`

## Remediation

Update Mattermost to versions 11.11.0, 11.10.1, 11.9.2, 11.8.6, 11.7.11 or higher.