MatterMost

By the Year

In 2026 there have been 161 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, 68 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-2026-96260	Sep 22, 2026	Mattermost <=11.10.1: CSRF request body DoS via plugins Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to enforce a request body size limit during CSRF validation of plugin requests which allows an authenticated user to exhaust server memory and cause a denial of service via a large request body sent to a plugin endpoint.. Mattermost Advisory ID: MMSA-2026-00775	Mattermost
CVE-2026-96259	Sep 22, 2026	Mattermost 11.9.x<=11.9.1 OAuth filter bypass, admin internal access Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to apply the internal-connection filter to OAuth endpoint requests, which allows a System Administrator to make the server issue requests to internal network addresses and read the responses via the configured OAuth token and userinfo endpoints.. Mattermost Advisory ID: MMSA-2026-00776	Mattermost
CVE-2026-95666	Sep 22, 2026	Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to limit the length of the post ID array accepted by the bulk reactions endpoint which Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to limit the length of the post ID array accepted by the bulk reactions endpoint which allows an authenticated user to cause excessive database load via a crafted request to {{POST /api/v4/posts/ids/reactions}}.. Mattermost Advisory ID: MMSA-2026-00771	Mattermost
CVE-2026-12284	Sep 17, 2026	Mattermost Desktop App <=6.2.2.0 IPC Sender Validation Bypass in leaveCall Mattermost Desktop App versions <=6.2 6.2.2.0 fails to validate the IPC sender in the leaveCall handler which allows a malicious or compromised Mattermost server (or a user with script access to a connected server view) to disconnect an active call belonging to a different connected server via the desktopAPI.leaveCall IPC message. Mattermost Advisory ID: MMSA-2026-00699	Mattermost
CVE-2026-75588	Sep 17, 2026	Mattermost Desktop <=6.2.2.0 URL Scheme Validation Bypass Mattermost Desktop App versions <=6.2 6.2.2.0 fail to validate the URL scheme when checking whether a target URL is internal to the connected server, which allows a network-positioned attacker to load a plugin popout window over an insecure connection via a link using a downgraded URL scheme. Mattermost Advisory ID: MMSA-2026-00717	Mattermost
CVE-2026-75025	Sep 16, 2026	Mattermost Desktop App versions <=6.2 6.2.2.0 Fixed an issue where Mattermost Desktop did not sufficiently restrict server-rendered content Mattermost Desktop App versions <=6.2 6.2.2.0 Fixed an issue where Mattermost Desktop did not sufficiently restrict server-rendered content from accessing local or private network resources. Thanks to game0v3r for contributing to this improvement under the Mattermost responsible disclosure policy. Mattermost Advisory ID: MMSA-2026-00698	Mattermost
CVE-2026-91181	Sep 14, 2026	Mattermost 11.9.x Data Retention API: Read-Only User Can Join Private Team 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 sanitize Team objects returned by the data retention teams endpoint which allows an authenticated user holding only the read-only Data Retention Policy permission to obtain a private team's secret invite_id and email, and use it to join the team without authorization, via GET /api/v4/data_retention/policies/{policy_id}/teams.. Mattermost Advisory ID: MMSA-2026-00702	Mattermost
CVE-2026-12985	Sep 14, 2026	Mattermost <=11.9.0 Unauth OAuth CR Bypass via Malformed URI Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7 Mattermost failed to validate Dynamic Client Registration redirect URIs by URL component (matching glob patterns against the raw URI string instead) which allows a remote unauthenticated attacker to register an OAuth client with an attacker-controlled callback host that bypasses the configured redirect URI allowlist via a crafted redirect URI that places an allowlisted host/path suffix inside the query string.. Mattermost Advisory ID: MMSA-2026-00700	Mattermost
CVE-2026-82920	Sep 14, 2026	Mattermost 11.9.x/11.8.x/11.7.x: Auth Bypass on Policy Update Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7 fail to enforce authorization boundaries on the access control policy update endpoint which allows a channel or team administrator to detach a system-assigned ABAC parent policy via a crafted PUT /api/v4/access_control_policies request with an empty imports list.. Mattermost Advisory ID: MMSA-2026-00724	Mattermost
CVE-2026-86348	Sep 14, 2026	Mattermost versions <=11.9 11.0.9 11.4.8 11.7.7 10.22.11.0 fail to recover from handler panics, which Mattermost versions <=11.9 11.0.9 11.4.8 11.7.7 10.22.11.0 fail to recover from handler panics, which allows an authenticated user to crash the plugin via a post-action request with an unexpected field type.. Mattermost Advisory ID: MMSA-2026-00701	Mattermost
CVE-2026-86349	Sep 14, 2026	Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.8, 10.11.x <= 10.11.22 fail to limit the nesting depth in the server-side Markdown parser which Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.8, 10.11.x <= 10.11.22 fail to limit the nesting depth in the server-side Markdown parser which allows an authenticated attacker to cause a denial of service (CPU resource exhaustion) via a crafted post containing deeply nested blockquotes or list items.. Mattermost Advisory ID: MMSA-2026-00707	Mattermost
CVE-2026-10556	Sep 14, 2026	Mattermost <=11.9.0 Null Payload Crash in MS Graph Webhook CVE-2026-10556 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 validate null entries in Microsoft Graph webhook notification payloads, which allows an unauthenticated attacker to crash the Microsoft Calendar plugin process and deny calendar integration service to all users on the instance via a crafted {{POST}} request to the public webhook endpoint.. Mattermost Advisory ID: MMSA-2026-00693	Mattermost
CVE-2026-13417	Sep 14, 2026	Mattermost Boards Plugin DoS via non-Object fields.properties (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 validate the type of `fields.properties` on block creation which allows an authenticated user with editor access to a board to crash the Boards plugin worker and trigger a denial of service via a child block whose `fields.properties` is a non-object value. Mattermost Advisory ID: MMSA-2026-00710	Mattermost
CVE-2026-9812	Sep 14, 2026	Mattermost 11.9.x <= 11.9.0 Run Property Validation Flaw Crash Playbooks 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 validate that a property field belongs to the specified run before updating its value which allows an authenticated user with run property-management access to crash the Playbooks plugin via a REST request referencing a property field that belongs to a different run. Mattermost Advisory ID: MMSA-2026-00684	Mattermost
CVE-2026-8821	Sep 14, 2026	Bypass channel memberperm in Mattermost 11.9.x10.11.22 CVE20268821 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 validate channel member-management permission during playbook run creation, allowing an authenticated channel member to add an arbitrary user to a restricted channel via the run owner field.. Mattermost Advisory ID: MMSA-2026-00677	Mattermost
CVE-2026-5132	Sep 14, 2026	Mattermost <1.12 DoS via oversized zlibcompressed SDP messages (v10.1111.9) 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 limit size of unpacked SDP messages compressed with zlib, which allows attacker to deny service or crash server via sending many SDP messages that unpack to large size.. Mattermost Advisory ID: MMSA-2026-00643	Mattermost
CVE-2026-15814	Sep 14, 2026	Mattermost DoS: Excessive Memory on Image Decode < 11.9 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 limit the amount of memory allocated when decoding uploaded image files which allows an authenticated user to cause excessive server memory consumption and potential denial of service via uploading a specially crafted image as a profile picture, channel file attachment, team icon, or custom brand image. Mattermost Advisory ID: MMSA-2026-00719	Mattermost
CVE-2026-10542	Sep 14, 2026	Mattermost 11.9.0 channel action ownership validation flaw 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 validate channel action ownership which allows channel managers to update actions in other channels via the channel action update endpoint.. Mattermost Advisory ID: MMSA-2026-00692	Mattermost
CVE-2026-14344	Sep 14, 2026	Mattermost 10.11.x-11.9.x: Unauthorized board-creation perm (CVE-2026-14344) 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 enforce the board-creation permission which allows an unauthorized authenticated user to create boards via the board duplicate, boards-and-blocks, and archive-import endpoints.. Mattermost Advisory ID: MMSA-2026-00715	Mattermost
CVE-2026-12882	Sep 14, 2026	Mattermost 11.9.x and prior: Markdown autolink parsing flaw causes DoS 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 parse Markdown autolinks with unmatched trailing closing parentheses in linear time, which allows an authenticated user with permission to create posts to cause excessive server CPU consumption and degrade availability for other users via specially crafted post or message attachment content. Mattermost Advisory ID: MMSA-2026-00703	Mattermost
CVE-2026-11993	Sep 14, 2026	Mattermost Goroutine Leak via Unchecked File Uploads (10.11-11.9) 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 enforce the limit of concurrent files being processed and handled failed files, which allows a user with permission to upload files to spawn more goroutines than intended and block the indexing of other files via uploading heavy files constantly to the server.. Mattermost Advisory ID: MMSA-2026-00696	Mattermost
CVE-2026-14259	Sep 14, 2026	Mattermost <=11.9 board creation bypass via import (CVE-2026-14259) 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 enforce board creation permissions when importing archive files which allows an authenticated non-guest team member to create Open or Private boards despite administrator restrictions via importing a crafted .boardarchive file. Mattermost Advisory ID: MMSA-2026-00712	Mattermost
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 limit decompressed content size and enforce the configured maximum file size in the Boards archive import handler, which allows an authenticated user to cause memory exhaustion or unbounded disk consumption via a crafted .boardarchive file uploaded to the import endpoint.. 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