VULNERABILITY INTELLIGENCE

CVE-2026-28759

CVSS score4.3 MEDIUM
EPSS probability0.15%
CISA KEVNot currently listed
Published2026-05-18
Last modified2026-10-14
CVSS vectorCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

Description

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate that a remote cluster has access to a channel before processing membership removal requests during shared channel membership sync, which allows a malicious remote cluster to remove any user from any channel, including private channels, via crafted membership sync messages targeting channels the remote cluster is not authorized to access. Mattermost Advisory ID: MMSA-2026-00576

Weakness classification

  • CWE-863: Incorrect Authorization

Primary references