GO-2026-5263 Mattermost doesn't verify channel membership when processing AI-assisted message rewrites in github.com/mattermost/mattermost-server

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

GO-2026-5067 Mattermost allows attackers to manipulate administrator terminals via crafted messages containing ANSI and OSC escape sequences in github.com/mattermost/mattermost-server

Mattermost allows attackers to manipulate administrator terminals via crafted messages containing ANSI and OSC escape sequences in github.com/mattermost/mattermost-server...

GO-2026-5112 Mattermost doesn't set permissions on downloaded bulk export in github.com/mattermost/mattermost-server

Mattermost doesn't set permissions on downloaded bulk export 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 causing false-positive reports from...

GO-2026-5173 Mattermost has an Incorrect Authorization issue in github.com/mattermost/mattermost-server

Mattermost has an Incorrect Authorization issue in github.com/mattermost/mattermost-server...

Incorrect Authorization

Overview github.com/mattermost/mattermost/server/v8/channels/api4 is a platform for secure collaboration across the entire software development lifecycle Affected versions of this package are vulnerable to Incorrect Authorization via the PUT /api/v4/users/id/active endpoint. An attacker can...

Mattermost Server 10.11.x < 10.11.14 / 11.5.x < 11.5.2 Vulnerability (MMSA-2025-00552)

The version of Mattermost Server installed on the remote host is affected by a vulnerability: - Mattermost fails to check if teamid was being changed when updating playbooks, allowing users with only Manage Playbook Configurations permission to change a playbook's team, bypassing manage members...

Mattermost Server 10.11.x < 10.11.14 / 11.4.x < 11.4.4 / 11.5.x < 11.5.2 Vulnerability (MMSA-2026-00597)

The version of Mattermost Server installed on the remote host is affected by a vulnerability: - Mattermost fails to enforce slash command trigger-word uniqueness during command updates which allows an authenticated team member with Manage Own Slash Commands permission to hijack and impersonate...

Incorrect Authorization

Overview Affected versions of this package are vulnerable to Incorrect Authorization via the schemeadmin flag in group syncable link and patch endpoints. An attacker can gain unauthorized administrative privileges by sending crafted API requests. Remediation Upgrade...

CVE-2026-6046 Plugin bot username conflict allows user account to be used as bot identity in Mattermost Server

Mattermost versions 11.6.x = 11.6.1, 11.5.x = 11.5.4, 10.11.x = 10.11.15, 10.11.x = 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels ...

CVE-2026-4635

Mattermost versions 11.6.x = 11.6.0, 11.5.x = 11.5.3, 11.4.x = 11.4.4, 10.11.x = 10.11.14 fail to archive the channel before removing persistent notifications which allows authenticated user to crash the server via timing the creation of persistent notification message between the server deleting...

Mattermost Server 10.11.x < 10.11.17 / 11.5.x < 11.5.5 / 11.6.x < 11.6.2 Improper Authorization (MMSA-2026-00629)

The version of Mattermost Server installed on the remote host is affected by a vulnerability as referenced in the MMSA-2026-00629 advisory. - Mattermost Server fails to validate team-level runcreate permission against the target team when creating a playbook run which allows an authenticated team...

Incorrect Authorization

Overview Affected versions of this package are vulnerable to Incorrect Authorization via the API response process. An attacker can access sensitive information about team member roles by invoking various team API endpoints without having elevated permissions. Remediation Upgrade...

Race Condition

Overview Affected versions of this package are vulnerable to Race Condition in the process responsible for handling persistent notifications due to a failure to archive the channel before removing existing notifications. An attacker can cause the server to crash by timing the creation of a...

CVE-2026-5740 Unauthenticated WebSocket binary frame causes denial of service in Mattermost Server

Mattermost versions 11.6.x = 11.6.0, 11.5.x = 11.5.3, 11.4.x = 11.4.4, 10.11.x = 10.11.14 fail to properly validate msgpack-encoded WebSocket frames before memory allocation which allows an unauthenticated remote attacker to crash the server process and cause a full service outage for all users v...

CVE-2026-5740 Unauthenticated WebSocket binary frame causes denial of service in Mattermost Server

Mattermost versions 11.6.x = 11.6.0, 11.5.x = 11.5.3, 11.4.x = 11.4.4, 10.11.x = 10.11.14 fail to properly validate msgpack-encoded WebSocket frames before memory allocation which allows an unauthenticated remote attacker to crash the server process and cause a full service outage for all users v...

CVE-2026-5740

Mattermost CVE-2026-5740 is an unauthenticated denial-of-service issue affecting Mattermost Server versions 11.6.x up to 11.6.0, 11.5.x up to 11.5.3, 11.4.x up to 11.4.4, and 10.11.x up to 10.11.14. The root cause is improper validation of msgpack-encoded WebSocket frames before memory allocation...

Mattermost Server 10.11.x <= 10.11.13 / 11.5.x <= 11.5.1 Multiple Vulnerabilities (MMSA-2026-00570 / MMSA-2026-00575 / MMSA-2026-00582 / MMSA-2026-00622)

The version of Mattermost Server installed on the remote host is affected by multiple vulnerabilities: - Mattermost fails to validate the Host header when constructing response URLs for custom slash commands which allows an authenticated attacker to redirect slash command responses to an...

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...

Incorrect Authorization

Overview Affected versions of this package are vulnerable to Incorrect Authorization via the command update API. An attacker can impersonate existing system or custom commands by editing their own slash command trigger to match an already-registered trigger, potentially hijacking command...

Insertion of Sensitive Information into Log File

Overview Affected versions of this package are vulnerable to Insertion of Sensitive Information into Log File via the support packet generation process. An attacker can access sensitive credentials in plaintext by downloading a support packet from the System Console. This is only exploitable if t...