CVE-2026-8821: Missing Authorization

Mattermost versions 11.9.x = 11.9.0, 11.8.x = 11.8.4, 11.7.x = 11.7.7, 10.11.x = 10.11.22 fail to validate channel member-management permission during playbook run creation, allowing an authenticated channel member to add an arbitrary user to a restricted channel via the run owner field...

CVE-2026-16048

Mattermost versions 11.8.x = 11.8.2, 11.7.x = 11.7.6, 10.11.x = 10.11.21 fail to restrict channel member role assignment to channel-scoped roles which allows a channel administrator to gain additional channel permissions via the channel member roles API.. Mattermost Advisory ID: MMSA-2026-00697...

CVE-2026-16048 Channel member roles accept out-of-scope roles

Mattermost versions 11.8.x = 11.8.2, 11.7.x = 11.7.6, 10.11.x = 10.11.21 fail to restrict channel member role assignment to channel-scoped roles which allows a channel administrator to gain additional channel permissions via the channel member roles API.. Mattermost Advisory ID: MMSA-2026-00697...

CVE-2026-16048

Mattermost versions 11.8.x = 11.8.2, 11.7.x = 11.7.6, 10.11.x = 10.11.21 fail to restrict channel member role assignment to channel-scoped roles which allows a channel administrator to gain additional channel permissions via the channel member roles API.. Mattermost Advisory ID: MMSA-2026-00697...

PT-2026-76662

Mattermost versions 11.8.x = 11.8.2, 11.7.x = 11.7.6, 10.11.x = 10.11.21 fail to restrict channel member role assignment to channel-scoped roles which allows a channel administrator to gain additional channel permissions via the channel member roles API.. Mattermost Advisory ID: MMSA-2026-00697...

CVE-2026-8075

Mattermost Desktop App versions =6.2 5.5.13 6.0.2.0 fail to properly null check when checking for headers in the Mattermost Desktop App which allows any user to crash another channel members Desktop App via posting a malicious link with an embedded image that misses one of those headers. Mattermo...

The vulnerability of the is_user_channelmember() function in the Open WebUI artificial intelligence-based web interface allows a intruder to bypass existing security mechanisms and gain access to read and modify data.

The vulnerability of the isuserchannelmember function in the Open WebUI artificial intelligence-based web interface is related to the lack of restrictions on access to API keys. Exploiting this vulnerability could allow a malicious actor to bypass existing security mechanisms and gain access to...

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...

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: Origin Validation Error

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-2026-45385 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...

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...

Discourse Information Disclosure Vulnerability (CNVD-2026-17255)

Discourse is Discourse open source set of open source community discussion platform. The platform includes features such as community , e-mail and chat rooms . Discourse suffers from an information disclosure vulnerability that stems from the possibility of inferring the identity of a channel...

Discourse 信息泄露漏洞

Discourse is Discourse open source set of open source community discussion platform. The platform includes features such as community , e-mail and chat rooms . Discourse suffers from an information disclosure vulnerability that stems from the possibility of inferring the identity of a channel...

CVE-2025-1792

Mattermost versions 10.7.x = 10.7.0, 10.5.x = 10.5.3, 9.11.x = 9.11.12 fail to properly enforce access controls for guest users accessing channel member information, allowing authenticated guest users to view metadata about members of public channels via the channel members API endpoint...

SUSE CVE-2025-11777

Mattermost versions 10.11.x = 10.11.3, 10.5.x = 10.5.11 fail to properly validate team membership permissions in the Add Channel Member API which allows users from one team to access user metadata and channel membership information from other teams via the API endpoint...

SUSE CVE-2025-55074

Mattermost versions 10.11.x = 10.11.3, 10.5.x = 10.5.11 fail to enforce access permissions on the Agents plugin which allows other users to determine when users had read channels via channel member objects...

CVE-2025-55074

Mattermost versions 10.11.x = 10.11.3, 10.5.x = 10.5.11 fail to enforce access permissions on the Agents plugin which allows other users to determine when users had read channels via channel member objects...

GO-2025-4133 Mattermost allows other users to determine when users had read channels via channel member objects in github.com/mattermost/mattermost-server

Mattermost allows other users to determine when users had read channels via channel member objects in github.com/mattermost/mattermost-server. NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions. If this is...

Mattermost Server 10.5.x < 10.5.12 / 10.11.x 10.11.4 / 11.0.0 Missing Authorization (MMSA-2025-00518)

The version of Mattermost Server installed on the remote host is affected by a vulnerability as referenced in the MMSA-2025-00518 advisory. - Mattermost versions 10.11.x = 10.11.3, 10.5.x = 10.5.11 fail to properly validate team membership permissions in the Add Channel Member API which allows...