---
id: CVE-2026-18223
title: >-
  Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1,
  11.8.x <= 11.8.5 fail to validate the invited recipient's email address when
  redeeming team and guest invitation tokens, which allows an authenticated
  attacker t…
summary: >-
  Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1,
  11.8.x <= 11.8.5 fail to validate the invited recipient's email address when
  redeeming team and guest invitation tokens, which allows an authenticated
  attacker t…
severity: medium
cvss: 5
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:L/A:N'
cwe:
  - CWE-863
vendor: Mattermost
product: Mattermost
affected:
  - Mattermost >= 11.10.0 <= 11.10.0
  - Mattermost >= 11.7.0 <= 11.7.9
  - Mattermost >= 11.9.0 <= 11.9.1
  - Mattermost >= 11.8.0 <= 11.8.5
published: '2026-10-16'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T19:23:18.623'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-18223'
references:
  - url: 'https://mattermost.com/security-updates'
    label: responsibledisclosure@mattermost.com
tags:
  - nvd
  - cve.org
epss: 0.00161
epssPercentile: 0.05192
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-10-16T14:16:18.832947Z'
ingestedAt: '2026-10-16T08:02:23.120Z'
---

## Overview

Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to validate the invited recipient's email address when redeeming team and guest invitation tokens, which allows an authenticated attacker to join a team or gain unauthorized access to private channels via a forwarded or leaked invitation link.. Mattermost Advisory ID: MMSA-2026-00747

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.