CVE-2026-28759 Insufficient authorization in shared channel membership sync allows remote cluster to remove users from arbitrary channels

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,...

CVE-2026-28759

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,...

CVE-2026-28759 Insufficient authorization in shared channel membership sync allows remote cluster to remove users from arbitrary channels

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,...

CVE-2026-28759 Insufficient authorization in shared channel membership sync allows remote cluster to remove users from arbitrary channels

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,...

CVE-2026-4273: Incorrect Authorization

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13 fail to validate that the RefreshedToken differs from the original invite token during remote cluster invite confirmation which allows an authenticated attacker to bypass token rotation and reuse the original invite token via sending a craft...

PT-2026-41643

Name of the Vulnerable Software and Affected Versions Mattermost versions 11.5.0 through 11.5.1 Mattermost versions 10.11.0 through 10.11.13 Description Insufficient token rotation validation occurs during remote cluster invite confirmation. An authenticated attacker can bypass token rotation and...

PT-2026-41640

Name of the Vulnerable Software and Affected Versions Mattermost versions 11.5.0 through 11.5.1 Mattermost versions 10.11.0 through 10.11.13 Mattermost versions 11.4.0 through 11.4.3 Description An issue exists during shared channel membership sync where the system fails to validate if a remote...

CVE-2026-28759: Incorrect Authorization

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,...

EUVD-2026-16162

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...

GHSA-G7FP-CQJ5-X8HF Mattermost has an Incorrect Authorization issue

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...

Mattermost has an Incorrect Authorization issue

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...

Incorrect Authorization

Overview Affected versions of this package are vulnerable to Incorrect Authorization in the membership synchronization process. An attacker can gain unauthorized access to an entire private team by sending crafted membership synchronization messages from a remote cluster that trigger team...

CVE-2026-4274

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...

CVE-2026-4274

Mattermost CVE-2026-4274 affects multiple release lines: 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, and 11.3.x

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 cluster, which allows a malicious remote cluster to grant a user access to an entire private team instead of only the shared...

CVE-2026-4274

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...

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 cluster, which allows a malicious remote cluster to grant a user access to an entire private team instead of only the shared...

CVE-2026-4274: Incorrect Authorization

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...

PT-2026-28642

Name of the Vulnerable Software and Affected Versions Mattermost versions 10.11.0 through 10.11.10 Mattermost versions 11.2.0 through 11.2.2 Mattermost versions 11.3.0 through 11.3.1 Mattermost versions 11.4.0 Description The software does not properly restrict team-level access when processing...

CVE-2019-11497

In Couchbase Server 5.0.0, when an invalid Remote Cluster Certificate was entered as part of the reference creation, XDCR did not parse and check the certificate signature. It then accepted the invalid certificate and attempted to use it to establish future connections to the remote cluster. This...