CVE-2026-18551 — Mattermost guest account privilege escalation via member roles API

CVE-2026-18551

Mattermost guest account privilege escalation via member roles API PUBLISHED

Description (CNA)

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

Affected (CNA)

Vendor / product	Versions
Mattermost / Mattermost	affected 11.10.0 through 11.10.0; affected 11.7.0 through 11.7.9; affected 11.9.0 through 11.9.1; affected 11.8.0 through 11.8.5; unaffected 11.11.0; unaffected 11.10.1; unaffected 11.7.10; unaffected 11.9.2; unaffected 11.8.6

CWE

CWE-863

References

https://mattermost.com/security-updates

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.