CVE-2026-18551
Received Received - Intake

Privilege Escalation in Mattermost via Role Manipulation

Publication date: 2026-10-16

Last updated on: 2026-10-16

Assigner: Mattermost, Inc.

Description
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 combination of guest and admin scheme roles which allows an authenticated attacker to escalate a guest account to team or channel admin via a crafted PUT request to the member roles API endpoint.. Mattermost Advisory ID: MMSA-2026-00752

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published
2026-10-16
Last Modified
2026-10-16
Generated
2026-10-16
AI Q&A
2026-10-16
EPSS Evaluated
N/A
NVD
CVE-2026-18551
EUVD
EUVD-2026-102806

Affected Vendors & Products

Showing 4 associated CPEs
Vendor Product Version / Range
Mattermost Mattermost 11.10.0
Mattermost Mattermost 11.7.0
Mattermost Mattermost 11.9.0
Mattermost Mattermost 11.8.0

Helpful Resources

Exploitability

CWE
CWE Icon
KEV
KEV Icon
CWE ID Description
CWE-863 The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.

Attack-Flow Graph

AI Quick Actions

Instant insights powered by AI
Executive Summary

Mattermost versions between 11.7.9 and 11.10.0 have a flaw where guest accounts can be escalated to team or channel admin roles. The issue occurs because the system fails to properly validate role combinations when processing a crafted PUT request to the member roles API endpoint.

Impact Analysis

An authenticated attacker could exploit this to gain elevated privileges, potentially accessing sensitive data or performing unauthorized actions within the Mattermost platform. This could lead to data breaches or system compromise depending on the attacker's goals.

Mitigation Strategies

Immediately upgrade Mattermost to a patched version that addresses the vulnerability. Check the Mattermost Security Updates page for the latest fixed releases.

Chat Assistant

Ask questions about this CVE
Hi! I’m here to help you understand CVE-2026-18551. Ask me anything about the vulnerability, its impact, or mitigation strategies.
0/70

EPSS Chart