| Summary | 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 |
|---|---|
| Publication Date | May 18, 2026, 5:16 p.m. |
| Registration Date | May 19, 2026, 4:14 a.m. |
| Last Update | May 19, 2026, 2:32 a.m. |
| CVSS3.1 : MEDIUM | |
| スコア | 4.3 |
|---|---|
| Vector | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N |
| 攻撃元区分(AV) | ネットワーク |
| 攻撃条件の複雑さ(AC) | 低 |
| 攻撃に必要な特権レベル(PR) | 低 |
| 利用者の関与(UI) | 不要 |
| 影響の想定範囲(S) | 変更なし |
| 機密性への影響(C) | なし |
| 完全性への影響(I) | 低 |
| 可用性への影響(A) | なし |