Mattermost

Mattermost versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to prevent rendering of external SVGs on link embeds which allows unauthenticated users to crash the Mattermost webapp and desktop app via creating an issue or PR on GitHub.. Mattermost Advisory ID: MMSA-2026-00595Show less

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to handle incorrectly reported array lengths which allows malicious user to cause OOM errors and crash the server via sending corrupted msgpack frames within websocket messages to calls plugin. Mattermost Advisory ID: MMSA-2025-00537Show less

Mattermost versions 10.11.x <= 10.11.10 fail to properly validate permission requirements in the team member roles API endpoint which allows team administrators to demote members to guest role. Mattermost Advisory ID: MMSA-2025-00531Show less

Mattermost versions 10.11.x <= 10.11.10 Fail to invalidate cached permalink preview data when a user loses channel access which allows the user to continue viewing private channel content via previously cached permalink previews until cache reset or relogin.. Mattermost Advisory ID: MMSA-2026-00580Show less

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2 fail to verify run_create permission for empty playbookId, which allows team members to create unauthorized runs via the playbook run API. Mattermost Advisory ID: MMSA-2025-00542Show less

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to canonicalize IPv4-mapped IPv6 addresses before reserved IP validation which allows an attacker to perform SSRF attacks against internal services via IPv4-mapped IPv6 literals (e.g., [::ffff:127.0.0.1]).. Mattermost Advisory ID: MMSA-2026-00585Show less

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to properly enforce read permissions in search API endpoints which allows guest users without read permissions to access posts and files in channels via search API requests. Mattermost Advisory ID: MMSA-2025-00554Show less

Mattermost versions 10.11.x <= 10.11.10 fail to validate user's authentication method when processing account auth type switch which allows an authenticated attacker to change account password without confirmation via falsely claiming a different auth provider.. Mattermost Advisory ID: MMSA-2026-00583Show less

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to use consistent error responses when handling the /mute command which allows an authenticated team member to enumerate private channels they are not authorized to know about via differing error messages for nonexistent versus private channels. Mattermost Advisory ID: MMSA-2026-00588Show less

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to validate team-specific upload_file permissions which allows a guest user to post files in channels where they lack upload_file permission via uploading files in a team where they have permission and reusing the file metadata in a POST request to a different team. Mattermost Advisory ID: MMSA-2025-00553Show less

Mattermost versions 11.3.x <= 11.3.0 fail to preserve the redacted state of burn-on-read posts during deletion which allows channel members to access unrevealed burn-on-read message contents via the WebSocket post deletion event.. Mattermost Advisory ID: MMSA-2026-00579Show less

Mattermost Plugins versions <=2.0.3.0 fail to properly mask sensitive configuration values which allows an attacker with access to support packets to obtain original plugin settings via exported configuration data. Mattermost Advisory ID: MMSA-2026-00606Show less

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to filter invite IDs based on user permissions, which allows regular users to bypass access control restrictions and register unauthorized accounts via leaked invite IDs during team creation.. Mattermost Advisory ID: MMSA-2025-00565Show less

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to restrict plugin installation on CI test instances with default admin credentials which allows an unauthenticated attacker to achieve remote code execution and exfiltrate sensitive configuration data including AWS and SMTP credentials via uploading a malicious plugin after changing the import directory. Mattermost Advisory ID: MMSA-2025-00528Show less

Mattermost Plugins versions <=11.3 11.0.3 11.2.2 10.10.11.0 fail to implement authorisation checks on comment block modifications, which allows an authorised attacker with editor permission to modify comments created by other board members. Mattermost Advisory ID: MMSA-2025-00559Show less

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to properly validate team membership when searching channels which allows a removed team member to enumerate all public channels within a private team via the channel search API endpoint.. Mattermost Advisory ID: MMSA-2025-00568Show less

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to sanitize client-supplied post metadata which allows an authenticated attacker to spoof permalink embeds impersonating other users via crafted PUT requests to the post update API endpoint.. Mattermost Advisory ID: MMSA-2025-00569Show less

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 Mattermost fails to limit the size of responses from integration action endpoints, which allows an authenticated attacker to cause server memory exhaustion and denial of service via a malicious integration server that returns an arbitrarily large response when a user clicks an interactive message button.. Mattermost Advisory ID: MMSA-2026-00571Show less

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to bound memory allocation when processing PSD image files which allows an authenticated attacker to cause server memory exhaustion and denial of service via uploading a specially crafted PSD file. Mattermost Advisory ID: MMSA-2026-00572Show less

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to properly validate User-Agent header tokens which allows an authenticated attacker to cause a request panic via a specially crafted User-Agent header. Mattermost Advisory ID: MMSA-2026-00586Show less