CVE-2026-26230: Team Admin Privilege Escalation to Demote Members to Guest

Severity: low (CVSS 3.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-16 · updated 2026-06-17
Weakness: CWE-863

Description

Mattermost versions 10.11.x <= 10.11.10 fail to properly validate permission requirements in the team member roles API endpoint which allows team administrators to demote members to guest role. Mattermost Advisory ID: MMSA-2025-00531

Affected products

Mattermost: from 10.11.0 before 10.11.11 — fixed in 10.11.11

How to fix

Upgrade to a fixed version: Mattermost 10.11.11. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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