Incorrect Authorization

Overview Affected versions of this package are vulnerable to Incorrect Authorization in the invite confirmation process due to insufficient validation of the RefreshedToken. An attacker can bypass intended token rotation and reuse an original invite token by sending a crafted invite confirmation...

Missing Authorization

Overview Affected versions of this package are vulnerable to Missing Authorization via the post update and patch API endpoints. An attacker can modify existing posts despite lacking posting privileges by sending crafted API requests. Remediation Upgrade...

Incorrect Authorization

Overview Affected versions of this package are vulnerable to Incorrect Authorization via the API-level authorization process. An attacker can create issues or attach comments to a locked group by sending direct API requests as a member of multiple groups. Remediation Upgrade...

Authentication Bypass by Primary Weakness

Overview github.com/mattermost/mattermost/server/channels/app is a private-cloud Slack alternative Affected versions of this package are vulnerable to Authentication Bypass by Primary Weakness in the OAuth authorization code redemption process. An attacker can gain unauthorized access to resource...

GHSA-GVG4-JHMR-6J23 Mattermost doesn't check if {{team_id}} was being changed when updating playbooks

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13 fail 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 restriction via PUT api. Mattermost Advisory ID:...

GHSA-VQP5-2MRP-QQXG Mattermost doesn't validate the Host header when constructing response URLs for custom slash command

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13 fail 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 attacker-controlled server via a spoofed Host header.. Mattermost...

GHSA-WVGV-4FC3-2RCP Mattermost doesn't prevent disclosure of created user password

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13, 11.4.x = 11.4.3 doesn't prevent disclosure of created user password which allows a malicious attacker to impersonate a user via the use of some of those passwords.. Mattermost Advisory ID: MMSA-2026-00614...

GHSA-9P64-JPC7-M2RP Mattermost doesn't sanitize sensitive configuration fields before including them in support packet generation

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13, 11.4.x = 11.4.3 fail to sanitize sensitive configuration fields before including them in support packet generation, which allows a Mattermost System Admin or any party with access to a support packet to obtain sensitive credentials in...

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...

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...

Mattermost doesn't check if {{team_id}} was being changed when updating playbooks

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13 fail 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 restriction via PUT api. Mattermost Advisory ID:...

GHSA-82J6-4FQ7-FX62 Mattermost doesn't sanitize sensitive configuration fields in the Mattermost Calls plugin

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13, 11.4.x = 11.4.3 fail to sanitize sensitive configuration fields in the Mattermost Calls plugin which allows an attacker with access to a support packet to obtain TURN server credentials via the plaintext values present in the exported plugi...

GHSA-M79Q-8QF5-V622 Mattermost doesn't check public/private permissions

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13, 11.4.x = 11.4.3 fail to check public/private permissions which allows members without these permissions to access public playbooks via /get.. Mattermost Advisory ID: MMSA-2026-00591...

Mattermost doesn't validate the Host header when constructing response URLs for custom slash command

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13 fail 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 attacker-controlled server via a spoofed Host header.. Mattermost...

Mattermost doesn't sanitize sensitive configuration fields before including them in support packet generation

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13, 11.4.x = 11.4.3 fail to sanitize sensitive configuration fields before including them in support packet generation, which allows a Mattermost System Admin or any party with access to a support packet to obtain sensitive credentials in...

Mattermost doesn't prevent disclosure of created user password

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13, 11.4.x = 11.4.3 doesn't prevent disclosure of created user password which allows a malicious attacker to impersonate a user via the use of some of those passwords.. Mattermost Advisory ID: MMSA-2026-00614...

Mattermost doesn't sanitize sensitive configuration fields in the Mattermost Calls plugin

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13, 11.4.x = 11.4.3 fail to sanitize sensitive configuration fields in the Mattermost Calls plugin which allows an attacker with access to a support packet to obtain TURN server credentials via the plaintext values present in the exported plugi...

Mattermost doesn't check public/private permissions

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13, 11.4.x = 11.4.3 fail to check public/private permissions which allows members without these permissions to access public playbooks via /get.. Mattermost Advisory ID: MMSA-2026-00591...

Allocation of Resources Without Limits or Throttling

Overview Affected versions of this package are vulnerable to Allocation of Resources Without Limits or Throttling via the start meeting API endpoint when the size of the request body is not limited. An attacker can exhaust system resources or disrupt service availability by sending crafted...