CVE-2026-4274 — Insufficient authorization in shared channel membership sync grants team-level access instead of channel-level access
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 restrict team-level access when processing membership sync from a remote cl…
Published: 2026-03-26 · CVSS: 5.4 · CVSS 3.1
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 restrict team-level access when processing membership sync from a remote cluster, which allows a malicious remote cluster to grant a user access to an entire private team instead of only the shared channel via sending crafted membership sync messages that trigger team membership assignment. Mattermost Advisory ID: MMSA-2026-00574
Source: CVE Program · Revision 8b16575c39f1e1810c5e863010da073d2d3285e7