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,...

Mattermost Server 11.5.x < 11.5.2 Missing Authorization (MMSA-2026-00645)

The version of Mattermost Server installed on the remote host is affected by a vulnerability as referenced in the MMSA-2026-00645 advisory. - Mattermost versions 11.5.x = 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker t...

GHSA-8R89-8W26-CQ32 Mattermost doesn't verify channel membership when processing AI-assisted message rewrites

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...

Mattermost doesn't verify channel membership when processing AI-assisted message rewrites

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

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...

PT-2026-41640

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,...

PT-2026-41655

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-2026-45385 Open WebUI: An IDOR vulnerability exists in the update_message_by_id API endpoint

Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.9.5, an IDOR vulnerability exists in the Channels feature of Open WebUI, allowing any channel member to modify messages sent by other members including administrators within the same...

EUVD-2026-30619

Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.9.0, the isuserchannelmember function checks whether a ChannelMember row exists but does not check the isactive field. When a user is deactivated from a group or DM channel removed by the...

CVE-2026-44561

Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.9.0, the isuserchannelmember function checks whether a ChannelMember row exists but does not check the isactive field. When a user is deactivated from a group or DM channel removed by the...

GHSA-HMGR-67HW-J2CQ Open WebUI: Deactivated Channel Members Retain Full Access to Group/DM Channels

Deactivated Channel Members Retain Full Access to Group/DM Channels Affected Component Channel membership authorization check: - backend/openwebui/models/channels.py lines 663-673, isuserchannelmember - Used at 15 locations in backend/openwebui/routers/channels.py Affected Versions Current main...

Open WebUI: Deactivated Channel Members Retain Full Access to Group/DM Channels

Deactivated Channel Members Retain Full Access to Group/DM Channels Affected Component Channel membership authorization check: - backend/openwebui/models/channels.py lines 663-673, isuserchannelmember - Used at 15 locations in backend/openwebui/routers/channels.py Affected Versions Current main...

Improper Authorization

github.com/mattermost/mattermost-server is vulnerable to improper authorization. The vulnerability is due to insufficient validation of team membership permissions in the Add Channel Member API, which allows an attacker to exploit the API endpoint to access user metadata and channel membership...

PT-2026-39278

Name of the Vulnerable Software and Affected Versions Open WebUI versions prior to 0.9.0 Description In the self-hosted artificial intelligence platform Open WebUI, the is user channel member function fails to verify the is active field when checking channel membership. When a user is removed fro...

Improper Access Control

github.com/mattermost/mattermost-server is vulnerable to improper access control. The vulnerability is due to failure to validate user channel membership when attaching posts to Jira issues, which allows an authenticated attacker with Jira plugin access to read post content and attachments from...

BIT-DISCOURSE-2026-32618 Discourse: Unauthorized channel membership inference via excluded_memberships_channel_id

Discourse is an open-source discussion platform. From versions 2026.1.0 to before 2026.1.3, and 2026.2.0 to before 2026.2.2, there is possible channel membership inference from chat user search without authorization. This issue has been patched in versions 2026.1.3, 2026.2.2, and 2026.3.0...

CVE-2026-32618

Discourse is an open-source discussion platform. From versions 2026.1.0-latest to before 2026.1.3, 2026.2.0-latest to before 2026.2.2, and 2026.3.0-latest to before 2026.3.0, there is possible channel membership inference from chat user search without authorization. This issue has been patched in...