GHSA-XVCX-MGPC-5XH3 Mattermost doesn't validate the X-Requested-With header on the burn-on-read reveal endpoint

Mattermost versions 11.5.x = 11.5.1, 11.4.x = 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost...

GHSA-8H9W-W78C-VVR3 Mattermost does not verify remote cluster channel access when processing shared channel membership removals

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,...

Mattermost does not verify remote cluster channel access when processing shared channel membership removals

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-2026-5163

Mattermost versions 11.5.x = 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private channels and direct messages they do not have access to via a crafted request to the post rewrite...

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-2026-5163

Mattermost versions 11.5.x = 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private channels and direct messages they do not have access to via a crafted request to the post rewrite...

CVE-2026-5163 Missing authorization check in AI message rewrite endpoint allows access to private thread content

Mattermost versions 11.5.x = 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private channels and direct messages they do not have access to via a crafted request to the post rewrite...

CVE-2026-6339 Missing request origin validation on burn-on-read reveal endpoint

Mattermost versions 11.5.x = 11.5.1, 11.4.x = 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost...

EUVD-2026-30749

Mattermost versions 11.5.x = 11.5.1, 11.4.x = 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost...

CVE-2026-6339 Missing request origin validation on burn-on-read reveal endpoint

Mattermost versions 11.5.x = 11.5.1, 11.4.x = 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost...

CVE-2026-3637 Mattermost fails to enforce create_post permission when editing posts

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13, 11.4.x = 11.4.3 fail to check the createpost channel permission during post edit operations which allows an authenticated attacker with revoked posting privileges to modify their existing posts via direct API requests to the post update and...

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,...

EUVD-2026-30738

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 multiple releases (11.4.x <= 11.4.3, 11.5.x <= 11.5.1, 10.11.x

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,...

BIT-POSTGRESQL-2026-6478 PostgreSQL discloses MD5-hashed passwords via covert timing channel

Covert timing channel in comparison of MD5-hashed password in PostgreSQL authentication allows an attacker to recover user credentials sufficient to authenticate. This does not affect scram-sha-256 passwords, the default in all supported releases. However, current databases may have MD5-hashed...

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...

PT-2026-41655

Name of the Vulnerable Software and Affected Versions Mattermost versions 11.5.x through 11.5.1 Description An issue exists where channel membership is not verified during the processing of AI-assisted message rewrites. This allows an authenticated attacker to read the content of threads in priva...