EUVD-2026-15806

Mattermost versions 11.2.x = 11.2.2, 10.11.x = 10.11.10, 11.4.x = 11.4.0, 11.3.x = 11.3.1 fail to properly validate CSRF tokens in the /api/v4/accesscontrolpolicies/policyid/activate endpoint, which allows an attacker to trick an admin into changing access control policy active status via a craft...

CVE-2026-26304

Mattermost versions 11.3.x = 11.3.0, 11.2.x = 11.2.2 fail to verify runcreate permission for empty playbookId, which allows team members to create unauthorized runs via the playbook run API. Mattermost Advisory ID: MMSA-2025-00542...

CVE-2026-2456

Mattermost is affected by CVE-2026-2456 due to an unbounded memory allocation when handling responses from integration action endpoints. A authenticated attacker can cause server memory exhaustion and a denial of service by having a malicious integration server return an arbitrarily large respons...