Lack of permissions prompting when opening external URLs

Mattermost Desktop App versions <=5.7.0 fail to correctly prompt for permission when opening external URLs which allows a remote attacker to force a victim over the Internet to run arbitrary programs on the victim's system via custom URI schemes.

Bypass of TCC restrictions on macOS

Mattermost Desktop App versions <=5.7.0 fail to disable certain Electron debug flags which allows for bypassing TCC restrictions on macOS.

Lack of permission check when updating the profile picture of a remote user (shared channels enabled)

Mattermost versions 9.5.x <= 9.5.5 and 9.8.0, when using shared channels with multiple remote servers connected, fail to check that the remote server A requesting the server B to update the profile picture of a user is the remote that actually has the user as a local one . This allows a malicious remote A to change the profile images of users that belong to another remote server C that is connected to the server A.

LaTeX post content manipulation via renderer state leak across contexts

Mattermost Mobile Apps versions <=2.16.0 fail to protect against abuse of a globally shared MathJax state which allows an attacker to change the contents of a LateX post, by creating another post with specific macro definitions.

Incorrect Authorization leads to Channel Member Count Leak

Mattermost fails to check the required permissions in the POST /api/v4/channels/stats/member_count API resulting in channel member counts being leaked to a user without permissions.

Missing authorization allows users to access arbitrary security levels on Jira through webhooks (Jira Plugin)

Mattermost Jira Plugin handling subscriptions fails to check the security level of an incoming issue or limit it based on the user who created the subscription resulting in registered users on Jira being able to create webhooks that give them access to all Jira issues.

CSRF issue allows disconnecting a user's Jira connection through a simple post message (Jira Plugin)

Mattermost Jira Plugin fails to protect against logout CSRF allowing an attacker to post a specially crafted message that would disconnect a user's Jira connection in Mattermost only by viewing the message.

Denial of service in mattermost mobile apps and server via emoji reactions

Mattermost fails to check if a custom emoji reaction exists when sending it to a post and to limit the amount of custom emojis allowed to be added in a post, allowing an attacker sending a huge amount of non-existent custom emojis in a post to crash the mobile app of a user seeing the post and to crash the server due to overloading when clients attempt to retrive the aforementioned post. 

Mattermost version 2.10.0 and earlier fails to sanitize deeplink paths, which allows an attacker to perform CSRF attacks against the server.

Mattermost version 8.1.6 and earlier fails to sanitize channel mention data in posts, which allows an attacker to inject markup in the web client.

Client side path traversal due to lack of route parameters validation

Mattermost webapp fails to validate route parameters in/<TEAM_NAME>/channels/<CHANNEL_NAME> allowing an attacker to perform a client-side path traversal.

Insecure Direct Object Reference in /plugins/focalboard/ api/v2/users of Mattermost Boards

Mattermost fails to perform proper authorization in the /plugins/focalboard/api/v2/users endpoint allowing an attacker who is a guest user and knows the ID of another user to get their information (e.g. name, surname, nickname) via Mattermost Boards.

Denial of Service via Link Preview in /api/v4/redirect_location

Mattermost fails to properly sanitize the request to /api/v4/redirect_location allowing an attacker, sending a specially crafted request to /api/v4/redirect_location, to fill up the memory due to caching large items.

Password hash in response body after username update

Mattermost fails to properly sanitize the user object when updating the username, resulting in the password hash being included in the response body. 

Denial of Service via crashing the Calls Plugin

Mattermost fails to properly validate requests to the Calls plugin, allowing an attacker sending a request without a User Agent header to cause a panic and crash the Calls plugin

Regex DoS from a malicious server enrolled in Desktop

Mattermost fails to properly validate a RegExp built off the server URL path, allowing an attacker in control of an enrolled server to mount a Denial Of Service.

Lack of Hardening against media exploitation from a remote origin

Mattermost Desktop fails to correctly handle permissions or prompt the user for consent on certain sensitive ones allowing media exploitation from a malicious mattermost server

Mobile app freezes when receiving a post with hundreds of emojis

Mattermost Mobile fails to limit the maximum number of Markdown elements in a post allowing an attacker to send a post with hundreds of emojis to a channel and freeze the mobile app of users when viewing that particular channel. 

Mattermost Desktop logs all keystrokes during initial run after fresh installation 

Mattermost Desktop fails to set an appropriate log level during initial run after fresh installation resulting in logging all keystrokes including password entry being logged. 

Denial of Service via multiple identical User IDs in /api/v4/users/ids

Mattermost fails to deduplicate input IDs allowing a simple user to cause the application to consume excessive resources and possibly crash by sending a specially crafted request to /api/v4/users/ids with multiple identical IDs.