MatterMost

By the Year

In 2026 there have been 139 vulnerabilities in MatterMost with an average score of 5.2 out of ten. Last year, in 2025 MatterMost had 93 security vulnerabilities published. That is, 46 more vulnerabilities have already been reported in 2026 as compared to last year. However, the average CVE base score of the vulnerabilities in 2026 is greater by 0.06.

Recent MatterMost Security Vulnerabilities

CVE	Date	Vulnerability	Products
CVE-2026-75587	Aug 17, 2026	Mattermost Desktop App 6.2.2.0 Local Pre-Auth Secret Leak via Diagnostics Report Mattermost Desktop App versions <=6.2 6.2.2.0 fail to redact the pre-auth secret when generating a diagnostics report, which allows a local attacker with access to a user's diagnostics report or log files to obtain the plaintext pre-auth secret configured for a connected server via inspecting the Server Connectivity (Step-3) diagnostics output. Mattermost Advisory ID: MMSA-2026-00716	Mattermost
CVE-2026-9693	Aug 17, 2026	Thread Membership Record Leak in Mattermost Team Threads API <10.11.20,<11.7.5 Mattermost versions 10.11.x <= 10.11.20, 11.7.x <= 11.7.5 Mattermost fails to remove thread membership records when a user is removed from or leaves a team, which allows a previously removed user who is later re-invited to the team to view private channel thread root post content and metadata via the team threads API.. Mattermost Advisory ID: MMSA-2026-00682	Mattermost
CVE-2026-9859	Aug 17, 2026	Mattermost <11.8.4 Unchecked PMBR Allows Channel Hijack Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to enforce PermissionManageBoardRoles on the channelId field of the batch endpoint, which allows an authenticated board editor to relink any board they can edit to an arbitrary channel via a crafted PATCH request. Mattermost Advisory ID: MMSA-2026-00686	Mattermost
CVE-2026-9816	Aug 17, 2026	CVE-2026-9816: Mattermost <=11.7.6 Admin Escalation via Missing BoardMember.Scheme Validation Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to validate BoardMember.Scheme* fields server-side on insert and archive-import paths which allows a board editor or non-guest team member to grant board admin to arbitrary users via POST /api/v2/boards/{boardID}/members and POST /api/v2/teams/{teamID}/archive/import.. Mattermost Advisory ID: MMSA-2026-00685	Mattermost
CVE-2026-10080	Aug 17, 2026	Mattermost 11.8.3 WebSocket Cmd Type Validation Leading to DoS Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fails to validate WebSocket command field types which allows an authenticated user to crash the plugin process and deny service to all Boards users via a custom_focalboard_SUBSCRIBE_TEAM message with a non-string teamId.. Mattermost Advisory ID: MMSA-2026-00687	Mattermost
CVE-2026-10527	Aug 17, 2026	Mattermost <=11.8.3: SchemeAdmin bypass gives System Guest admin rights Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fails to reconcile SchemeAdmin flags with a user's current role which allows a user demoted to System Guest to retain Board Admin privileges and perform admin-only operations via the Boards REST API or UI.. Mattermost Advisory ID: MMSA-2026-00691	Mattermost
CVE-2026-15754	Aug 17, 2026	Access Control Bypass in Mattermost 11.7-11.8 via unassign API Mattermost versions 11.7.x <= 11.7.6, 11.8.x <= 11.8.3 The access control policy unassign endpoint fails to re-validate that each target channel still belongs to the requesting admin's team, which allows an authenticated team administrator to remove ABAC (attribute-based access control) policy assignments from channels outside their team via the policy unassign API after a channel has been moved to another team.. Mattermost Advisory ID: MMSA-2026-00718	Mattermost
CVE-2026-16044	Aug 17, 2026	Mattermost 11.7.6 Guest Escalation to Board Admin via .boardarchive Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21 fail to prevent guest users from receiving Board Admin privileges during board archive import which allows a board member to escalate a guest user to Board Admin via importing a crafted .boardarchive file. Mattermost Advisory ID: MMSA-2026-00672	Mattermost
CVE-2026-16045	Aug 17, 2026	Mattermost 10.11.x-10.11.21/11.7.x-11.7.6: OAuth Endpoints Unrestricted Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21 Mattermost failed to restrict OAuth deauthorization and personal access token management endpoints to direct user sessions, which allowed an OAuth app with a delegated user token to revoke the user's authorizations or tokens for other integrations via account-management endpoints.. Mattermost Advisory ID: MMSA-2026-00704	Mattermost
CVE-2026-16049	Aug 17, 2026	Mattermost GitLab Plugin <=11.8: Authenticated Injection via API (CVE-2026-16049) Mattermost Plugins versions <=11.8 10.20.11 11.5.7.0 _The Mattermost GitLab plugin fails to verify channel permissions when processing API requests with a caller-supplied_ {{post_id}}_, and fails to validate the_ {{web_url}} _parameter against the configured GitLab instance, which allows an authenticated attacker to inject bot-authored messages containing arbitrary URLs into channels they do not have access to via the_ {{createIssue}} _and_ {{attachCommentToIssue}} _API endpoints._ Mattermost Advisory ID: MMSA-2026-00673	Mattermost
CVE-2026-16047	Aug 17, 2026	Mattermost Inadequate Channel Access Validation in Board Linking 10.11-11.8 Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to validate that users have read access to a channel before linking a board to it, which allows an authenticated attacker to discover the membership of private channels on the same team via creating, patching, importing, or bulk-creating boards with an arbitrary channelId. Mattermost Advisory ID: MMSA-2026-00674	Mattermost
CVE-2026-16046	Aug 17, 2026	Mattermost <10.11.21 & <11.7.6: Undefined Run-State Validation Permits API Modification Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21 fail to enforce run-state validation on write operations for finished playbook runs which allows a run participant to modify status, checklists, retrospective content, ownership, and participants on completed runs via REST and GraphQL API requests. Mattermost Advisory ID: MMSA-2026-00675	Mattermost
CVE-2026-16048	Aug 17, 2026	Mattermost Channel Role Assignment Bypass via API (v10.11-11.8) 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	Mattermost
CVE-2026-14298	Aug 13, 2026	Mattermost DoS via Unchecked Resource Consumption in Auth'd Users (<=11.9.0) 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 properly limit resource consumption when processing certain user-supplied input, which allows an authenticated user to cause a denial of service. Mattermost Advisory ID: MMSA-2026-00713	Mattermost
CVE-2026-7521	Jul 28, 2026	Mattermost 10.11-11.8 Path Verify Flaw: Admin SAML Delete Arbitrary Files Mattermost versions 11.8.x <= 11.8.0, 11.7.x <= 11.7.3, 11.6.x <= 11.6.5, 10.11.x <= 10.11.20 fail to verify file deletion path which allows an admin with SAML system-console write permissions to delete arbitrary files outside the config directory from the server via the remove file endpoint.. Mattermost Advisory ID: MMSA-2026-00666	Mattermost
CVE-2026-10819	Jul 27, 2026	DoS in Mattermost 10.11.20-11.8.1 via Oversized GIF Custom Emoji Mattermost versions 11.6.x <= 11.6.5, 10.11.x <= 10.11.20, 11.8.x <= 11.8.1, 11.7.x <= 11.7.4 fail to limit the number of frames and enforce the file size cap on animated GIF uploads, which allows an authenticated attacker to cause a denial of service via a crafted animated GIF uploaded as a custom emoji.. Mattermost Advisory ID: MMSA-2026-00695	Mattermost
CVE-2026-10600	Jul 27, 2026	Mattermost 11.x DoS via Unbounded Server-side Doc Extraction Mattermost versions 11.8.x <= 11.8.0, 11.7.x <= 11.7.3, 11.6.x <= 11.6.5, 10.11.x <= 10.11.20 fail to bound the time and resource consumption of server-side document content extraction which allows an authenticated user with file-upload permission to degrade file uploads for all users on the server via repeatedly uploading small documents that are cheap to upload but expensive to extract, saturating the shared extraction worker pool.. Mattermost Advisory ID: MMSA-2026-00694	Mattermost
CVE-2026-8075	Jul 17, 2026	Mattermost Desktop App 6.2 Crash via Header Null Bug CVE20268075 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. Mattermost Advisory ID: MMSA-2026-00668	Mattermost
CVE-2026-9602	Jul 17, 2026	Mattermost Desktop App <=6.2 Crash via Malformed Payload in Web App Mattermost Desktop App versions <=6.2 6.0.2 5.6.13.0 fail to validate payloads sent from the Mattermost Web App to the Desktop App which allows a malicious server owner to crash the Mattermost Desktop App via changing the payload of a method to a malformed one. Mattermost Advisory ID: MMSA-2026-00678	Mattermost
CVE-2026-6541	Jul 13, 2026	CVE-2026-6541 Mattermost <=11.7.1 unauth playbook metric config change Mattermost versions 11.7.x <= 11.7.1, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to restrict metric configuration changes to the playbook being saved, which allows an authenticated user with team access to alter another users playbook metric settings via a crafted import or update request with a foreign metric ID. Mattermost Advisory ID: MMSA-2026-00653	Mattermost
CVE-2026-9820	Jul 13, 2026	Mattermost 10.11.19-11.7.2: Unsanitized Team Objects Privileged API Access Mattermost versions 11.7.x <= 11.7.2, 10.11.x <= 10.11.19 fail to sanitize team objects returned by the scheme teams endpoint, which allows a user with the User Manager role to obtain invite links for private teams and use them to join or share access to those teams via the scheme teams API endpoint.. Mattermost Advisory ID: MMSA-2026-00671	Mattermost
CVE-2026-9824	Jul 13, 2026	Mattermost 11.7.2/11.6.4/10.11.19 Bypass in /share-channel Autocomplete Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to check the manage_shared_channels permission in the /share-channel autocomplete handler, which allows an authenticated user without that permission to enumerate configured remote cluster connection metadata via slash command autocomplete.. Mattermost Advisory ID: MMSA-2026-00676	Mattermost
CVE-2026-9597	Jul 13, 2026	Mattermost 11.6-11.7 MagicLink Session Hijack (Deactivated Guest) Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4 fail to verify whether a guest account is deactivated before creating a session in the magic-link token login path, which allows a deactivated guest user to obtain a fully functional session via a magic-link token issued prior to deactivation.. Mattermost Advisory ID: MMSA-2026-00681	Mattermost
CVE-2026-6850	Jul 13, 2026	Mattermost 11.7.2: Markdown Parser DoS via Catastrophic Backtracking Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to validate the length and content of message attachment field values, which allows an authenticated attacker to cause a denial of service for all users in a channel via a post containing a specially crafted payload that triggers catastrophic backtracking in the client-side markdown parser.. Mattermost Advisory ID: MMSA-2026-00658	Mattermost
CVE-2026-10106	Jul 13, 2026	Mattermost 10-11.x Auth Bypass via Action Cookie Channel Mismatch Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to verify that the channel referenced in an action cookie matches the channel of the target post, which allows an authenticated user without access to a private channel to trigger interactive post actions on posts in that channel via a cookie obtained from any accessible channel.. Mattermost Advisory ID: MMSA-2026-00690	Mattermost
CVE-2026-10085	Jul 13, 2026	Mattermost 11.7.2-10.11.19 Group Sync Channel Flag Bypass (Patch API) Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to restrict the group_constrained channel flag to public and private channels that support group synchronization, which allows an ordinary group or direct message member to remove all participants from the conversation via the channel patch API.. Mattermost Advisory ID: MMSA-2026-00688	Mattermost
CVE-2026-9708	Jul 13, 2026	Mattermost <11.7.2 Webhook Access Bypass (Impersonation) Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to validate that an assigned incoming webhook user has access to the target team or channel, which allows a requester with webhook management permissions to create posts or direct messages attributed to another user via crafted incoming webhook configuration and payloads.. Mattermost Advisory ID: MMSA-2026-00683	Mattermost
CVE-2026-10103	Jul 13, 2026	Mattermost: Auth. remote can modify/delete posts via inb sync handler (<11.7.2) Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to verify post ownership in the shared channel inbound sync handler, which allows an authenticated remote cluster to modify or delete posts authored by local users or other remotes via crafted sync messages referencing arbitrary post IDs in channels shared with that remote.. Mattermost Advisory ID: MMSA-2026-00689	Mattermost
CVE-2026-9571	Jul 13, 2026	Mattermost OAuth Token Invalidation on Deactivation (11.7.2/11.6.4/10.11.19) Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to invalidate OAuth refresh tokens upon user account deactivation, which allows a deactivated user or an attacker in possession of a valid refresh token to obtain new functional access tokens via the OAuth refresh token grant endpoint.. Mattermost Advisory ID: MMSA-2026-00680	Mattermost
CVE-2026-4339	Jun 26, 2026	CVE-2026-4339: SSRF via Unvalidated URLs in Mattermost Agents MCP (11.6.3) Mattermost versions 10.11.x <= 10.11.18, 11.6.x <= 11.6.3, 11.5.x <= 11.5.6 fail to validate attachment URLs against internal or private IP ranges in the Mattermost Agents plugin MCP server which allows an attacker with access to the MCP server in stdio mode to perform server-side request forgery (SSRF) and exfiltrate data from internal network services via supplying internal URLs as file attachments in post creation requests.. Mattermost Advisory ID: MMSA-2026-00635	Mattermost
CVE-2026-9699	Jun 26, 2026	Mattermost Plugins <=11.6: OpenAI API key leak via unsanitized error logs Mattermost Plugins versions <=11.6 10.18.11 11.3.6 11.6.5.0 fail to sanitize error responses from the OpenAI API before logging, which allows a user with access to server logs or support packets to obtain a valid or partially reconstructable OpenAI API key via inspection of mattermost.log entries generated during authentication failures. Mattermost Advisory ID: MMSA-2026-00609	Mattermost
CVE-2026-3472	Jun 26, 2026	Mattermost 10.11-11.6 Markdown Image Exfil via AI Bot Tool (Auth) Mattermost versions 10.11.x <= 10.11.18, 11.6.x <= 11.6.3, 11.5.x <= 11.5.6 fail to properly apply markdown image rendering restrictions to AI bot tool result posts, which allows an authenticated attacker to exfiltrate data to an attacker-controlled server via injecting markdown image syntax into tool result content rendered by a victim's client.. Mattermost Advisory ID: MMSA-2026-00619	Mattermost
CVE-2026-13426	Jun 26, 2026	Mattermost Go Module <0.1.22 Path Validation Failure Enables API Redirect The Mattermost Go module github.com/mattermost/mattermost/server/public versions < v0.1.22 fail to validate path parameters when constructing API route paths which allows an attacker to redirect API calls to unintended endpoints via crafted IDs containing path traversal components. Mattermost Advisory ID: MMSA-2025-00532	Mattermost
CVE-2026-2299	Jun 25, 2026	Mattermost GMDrive Plugin <1.1.0 Authenticated File Share Disclosure The Mattermost Google Drive plugin before version 1.1.0 fails to validate channel membership in the file creation endpoint, allowing authenticated users with a connected Google account to share Google Drive files to unauthorized private channels and disclose private channel membership.	Mattermost
CVE-2026-8823	Jun 22, 2026	Mattermost 11.7.0: Admin can downgrade bots via demoteuser API Mattermost versions 11.7.x <= 11.7.0, 10.11.x <= 10.11.17 fail to validate bot targets when demoting users to guests which allows a lower-privileged administrator to degrade arbitrary bot accounts via the standard demote-user API.. Mattermost Advisory ID: MMSA-2026-00669	Mattermost
CVE-2026-6062	Jun 22, 2026	Unvalidated Channel Ownership in Mattermost Subscription Edit 10.11.17-11.7.x Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 Fail to validate channel ownership of an existing subscription before applying edits which allows an authenticated attacker to hijack subscriptions from channels they have no access to via a crafted PUT request to the subscription edit endpoint.. Mattermost Advisory ID: MMSA-2026-00650	Mattermost
CVE-2026-6673	Jun 22, 2026	Mattermost 11.7 Auth Bypass: Unauth POST /ac/installed SharedSecret Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 fail to authenticate Atlassian Connect installed callbacks, allowing a remote unauthenticated attacker to inject a rogue sharedSecret and disrupt the Jira integration via POST to /ac/installed during the pending-install window.. Mattermost Advisory ID: MMSA-2026-00654	Mattermost
CVE-2026-8074	Jun 22, 2026	Mattermost 10.11 <=10.11.17 / 11.7 <=11.7.0 API Perm Check Missing (CVE-2026-8074) Mattermost versions 11.7.x <= 11.7.0, 10.11.x <= 10.11.17 fail to enforce bot-specific permission checks on the user active status endpoint, which allows a User Manager with user management write access but no Integrations access to deactivate bot accounts via the PUT /api/v4/users/{id}/active API endpoint.. Mattermost Advisory ID: MMSA-2026-00667	Mattermost
CVE-2026-9162	Jun 22, 2026	Mattermost <10.11.17, 11.7.0 WS Auth Invalidation Flaw Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 fail to invalidate cached authentication state for active WebSocket connections during global session revocation, which allows a user with an existing WebSocket connection to remain authenticated and continue receiving real-time events until the cached session expires or the client reconnects.. Mattermost Advisory ID: MMSA-2026-00664	Mattermost
CVE-2026-5139	Jun 22, 2026	Mattermost <=11.7.0/11.6.2/11.5.5/10.11.17 Auth Bypass on /gitlab connect Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 fail to enforce administrator authorization on the {{setDefaultInstance}} call within the {{/gitlab connect}} command handler, which allows any authenticated user to overwrite the global default GitLab instance configuration via the {{/gitlab connect <instance-name>}} slash command.. Mattermost Advisory ID: MMSA-2026-00644	Mattermost
CVE-2026-8683	Jun 15, 2026	Mattermost Desktop App <=6.1 URL Overflow Crash via window.open Mattermost Desktop App versions <=6.1 5.5.13.0 fail to account for attempting to open extremely long URLs in the Mattermost Desktop App which allows a malicious server owner to crash the application via including a script to call window.open on a very large URL. Mattermost Advisory ID: MMSA-2026-00652	Mattermost
CVE-2026-6517	Jun 15, 2026	Mattermost Desktop App <=6.1 NTLM Credential Leakage via untrusted image domains Mattermost Desktop App versions <=6.1 5.5.13.0 fail to restrict the allow list of domains to which NTLM credentials were forwarded to in the Mattermost Desktop App which allows any user on a server without the image proxy enabled to intercept other users credentials via embedding an image that routes to an external web server. Mattermost Advisory ID: MMSA-2026-00651	Mattermost
CVE-2026-6961	Jun 12, 2026	Mattermost <=11.6.1/11.5.4 Path Traversal via FILEINFO.Name 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 Mattermost fails to sanitize FileInfo.Name received from federated peers during shared channel file sync, which allows an attacker who controls a federated server to write files to arbitrary locations within the target server's filestore via path traversal sequences in the filename field.. Mattermost Advisory ID: MMSA-2026-00661	Mattermost
CVE-2026-7387	Jun 12, 2026	Mattermost <=11.6.1 Auth Bypass via scheme_admin flag -> Priv Escalation 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 Mattermost fails to require role-management authorization when setting the scheme_admin flag on group syncable link and patch endpoints, which allows a user with group-link permissions to escalate themselves and group members to team or channel admin via crafted API requests.. Mattermost Advisory ID: MMSA-2026-00665	Mattermost
CVE-2026-6046	Jun 12, 2026	Mattermost Bot Registration Validation Bypass 10.11-11.6, Unprivileged Intercept 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 by pre-registering a user account with a predictable plugin bot username.. Mattermost Advisory ID: MMSA-2026-00649	Mattermost
CVE-2026-6689	Jun 12, 2026	Mattermost Team Creation Priv Escalation 10.11-11.6 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 enforce PermissionInviteUser when setting AllowOpenInvite or AllowedDomains during team creation (the check was only applied on update/patch), which allows an authenticated user holding PermissionCreateTeam but not PermissionInviteUser on the resulting team to configure invite-controlled team settings (make the team publicly joinable via open invite and/or constrain membership via allowed domains) that they are not permitted to set on an existing team via POST /api/v4/teams with allow_open_invite: true and/or a non-empty allowed_domains in the request body.. Mattermost Advisory ID: MMSA-2026-00655	Mattermost
CVE-2026-7184	Jun 12, 2026	Mattermost <=11.6.1 Remote Cluster API PATCH token leakage (CVE-2026-7184) Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15 fail to sanitize the Remote Cluster API response on PATCH operations, which allows authenticated users with the {{manage_secure_connections}} permission to obtain remote cluster authentication tokens via a PATCH request to the remote cluster endpoint.. Mattermost Advisory ID: MMSA-2026-00662	Mattermost
CVE-2026-6739	Jun 12, 2026	Privilege Escalation in Mattermost <=11.6.1 via Role Patch API 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 require system-level permission when patching protected default system roles, which allows authenticated users with delegated user-management permissions to escalate privileges by altering built-in role permissions via the role patch API.. Mattermost Advisory ID: MMSA-2026-00656	Mattermost
CVE-2026-3433	Jun 12, 2026	CVE-2026-3433: Mattermost 10.11.x-11.6 WebSocket role_updated Disclosure 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 restrict role_updated websocket event broadcasts to members of the affected team or channel which allows an authenticated attacker with guest-level access to observe permission scheme change notifications for private teams they are not a member of via the websocket connection.. Mattermost Advisory ID: MMSA-2026-00616	Mattermost
CVE-2026-6957	May 27, 2026	Mattermost 1.1.5 Arbitrary File Write via Unsanitized fn (CVE-2026-6957) Mattermost Plugins versions <=1.1.5 fail to sanitize filenames received from federated peers before using them to construct export destination paths, which allows an administrator of a remote federated Mattermost server to write files to arbitrary locations within the target server's filestore via a malicious filename delivered through the shared-channel attachment sync protocol. Mattermost Advisory ID: MMSA-2026-00659	Mattermost