CVE-2026-2457: Mattermost Server

Medium severity, CVSS 4.3. EPSS: 0.1% chance of exploitation in the next 30 days.

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to sanitize client-supplied post metadata which allows an authenticated attacker to spoof permalink embeds impersonating other users via crafted PUT requests to the post update API endpoint.. Mattermost Advisory ID: MMSA-2025-00569

Affected products

• Mattermost Mattermost Server: from 10.11.0, before 10.11.11 (fixed in 10.11.11); from 11.2.0, before 11.2.3 (fixed in 11.2.3); from 11.3.0, before 11.3.1 (fixed in 11.3.1)

Published 2026-03-16. Last modified 2026-06-17.