MatterMost

By the Year

In 2026 there have been 110 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, 17 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 0.07.

Recent MatterMost Security Vulnerabilities

CVE	Date	Vulnerability	Products
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
CVE-2026-4915	May 25, 2026	Mattermost <=11.6.0, 11.5.3, 11.4.4, 10.11.14 DoS via Null Webhook Attachment Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to filter nil elements from outgoing webhook attachment payloads before processing, which allows an authenticated user to cause a denial of service (server process termination) via a crafted webhook callback response containing a null attachment entry.. Mattermost Advisory ID: MMSA-2026-00641	Mattermost
CVE-2026-28735	May 22, 2026	Mattermost 10.11.x10.11.14 & 11.x11.6.0: OAuth Scope Bypass via GitHub URL Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate the OAuth token scope on the callback which allows an authenticated Mattermost user to gain access to private repositories via modifying the scope parameter in the GitHub authorization URL.. Mattermost Advisory ID: MMSA-2026-00628	Mattermost
CVE-2026-4635	May 22, 2026	Mattermost <= 11.6.0 Crash via Timing Delete Persistent Notification/Archive Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to archive the channel before removing persistent notifications which allows authenticated user to crash the server via timing the creation of persistent notification message between the server deleting existing persistent notifications and archiving the channel.. Mattermost Advisory ID: MMSA-2026-00637	Mattermost
CVE-2026-3473	May 22, 2026	Mattermost <11.6 Access Control Bypass via Boards API Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate file ownership and access control, which allows an authenticated user to access and download files belonging to other users or teams via crafted Boards API requests using valid file IDs.. Mattermost Advisory ID: MMSA-2026-00620	Mattermost
CVE-2026-4646	May 22, 2026	Mattermost API Input Validation flaw (v10.1111.6) causes plugin crash Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate user-supplied input in API request handlers which allows an authenticated attacker to crash the plugin process via a crafted HTTP request to the PR details endpoint.. Mattermost Advisory ID: MMSA-2026-00638	Mattermost
CVE-2026-3636	May 22, 2026	Mattermost API Data Leak: Unsanitized Team Member Data in 10.11.x-11.6.x Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to sanitize team member data when returned via API to users without elevated permissions which allows a user without permissions to get data about team members roles via invoking various team API endpoints.. Mattermost Advisory ID: MMSA-2026-00626	Mattermost
CVE-2026-5740	May 22, 2026	Mattermost <12 Allow Attacker Crashes Server via msgpack-WS Frame (CVE-2026-5740) Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to properly validate msgpack-encoded WebSocket frames before memory allocation which allows an unauthenticated remote attacker to crash the server process and cause a full service outage for all users via a crafted binary WebSocket message sent to the public WebSocket endpoint.. Mattermost Advisory ID: MMSA-2026-00647	Mattermost
CVE-2026-5308	May 22, 2026	Mattermost 10.11.0-11.6.0: Unchecked Body Size on Plugin Endpoints (DOS) Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to enforce request body size limits on plugin HTTP endpoints which allows an attacker to cause a denial of service via crafted oversized HTTP requests.. Mattermost Advisory ID: MMSA-2026-00646	Mattermost
CVE-2026-5755	May 22, 2026	Mattermost <=11.6.0 TIFF IFD OOM DoS via Crafted TIFF Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.2, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate the TIFF IFD offset in the image header before allocating memory, which allows authenticated users with file upload or posting permissions to cause a denial of service (server OOM) via uploading a crafted TIFF file or posting a URL that serves one.. Mattermost Advisory ID: MMSA-2026-00648	Mattermost
CVE-2026-22880	May 21, 2026	Mattermost Mobile App: SSO Callback Origin Validation Bypass (<=2.37, 11.x) Mattermost Mobile Apps versions <=2.37 11.4 2.0.37 11.0.4 11.1.3 11.3.2 10.11.11.0 fail to properly validate the SSO authentication callback origin which allows an attacker controlling a malicious Mattermost server to steal user credentials for a legitimate Mattermost server via relaying the SSO code exchange flow through the mobile application. Mattermost Advisory ID: MMSA-2025-00564	Mattermost
CVE-2026-4858	May 21, 2026	Mattermost 10.1111.6 Path Traversal in Integration Action URL (Auth User) Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to check integration URL for path traversal which allows an malicious authenticated user to call an arbitrary API via system admin Mattermost auth token using via path traversal in integration action URL.. Mattermost Advisory ID: MMSA-2026-00640	Mattermost
CVE-2026-4055	May 21, 2026	Mattermost 11.5.x <= 11.5.1 Playbook Run Create Auth Bypass Mattermost versions 11.5.x <= 11.5.1 fail to validate team-level run_create permission against the target team when creating a playbook run which allows an authenticated team member to create runs in teams where they lack permission via specifying a different team ID in the run creation API request. Mattermost Advisory ID: MMSA-2026-00629	Mattermost
CVE-2026-3471	May 18, 2026	Mattermost Desktop App <=6.1 URL Injection Crash via Popup Mattermost Desktop App versions <=6.1 6.0.1 5.4.13.0 fail to prevent an invalid URL from loading in a pop-up window in the Mattermost Desktop App which allows a malicious server owner to repeated crash the application via calling {{window.open('javascript:alert()');}}. Mattermost Advisory ID: MMSA-2026-00618	Mattermost
CVE-2026-4643	May 18, 2026	Mattermost Desktop App <=6.1 Crash via window.close() in Renderer Mattermost Desktop App versions <=6.1 6.0.1 5.4.13.0 fail to prevent server-rendered content from closing an underlying application view in the Mattermost Desktop App which allows a malicious server or plugin to crash the desktop client via invoking {{window.close()}} in the renderer context, leading to a denial of service condition at the client level. Mattermost Advisory ID: MMSA-2026-00633	Mattermost
CVE-2026-6333	May 18, 2026	Mattermost Host Header Bypass in Slash Commands v10.11 <=13, v11.5 <=1 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 Advisory ID: MMSA-2026-00582	Mattermost
CVE-2026-6345	May 18, 2026	Mattermost 10.11.13/11.5.1 Password Disclosure via User Creation Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail 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
CVE-2026-6346	May 18, 2026	Mattermost 11.5.1 Sensitive Config Leak via Support Pack 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 plaintext via downloading a support packet from the System Console.. Mattermost Advisory ID: MMSA-2026-00607	Mattermost
CVE-2026-28732	May 18, 2026	Mattermost 11.5.1 Slash Command Hijack via Uniqueness Bypass Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 Fail to enforce slash command trigger-word uniqueness during command updates which allows an authenticated team member with Manage Own Slash Commands permission to hijack and impersonate existing system or custom slash commands via editing their own slash command trigger to an already-registered trigger through the command update API. Mattermost Advisory ID: MMSA-2026-00597	Mattermost
CVE-2026-6343	May 18, 2026	Mattermost <= 11.5.1 Access Ctrl Bypass via Playbook Endpoint 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
CVE-2026-6347	May 18, 2026	Unsanitized Call Config in Mattermost <11.6 Exposes TURN Credentials 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 plugin configuration.. Mattermost Advisory ID: MMSA-2026-00605	Mattermost
CVE-2026-5163	May 18, 2026	Mattermost <=11.5.1: AI Rewrite Bypasses Channel Membership (CVE-2026-5163) 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 endpoint.. Mattermost Advisory ID: MMSA-2026-00645	Mattermost
CVE-2026-3117	May 18, 2026	Mattermost Gitlab Plugin Permissions Bypass CVE-2026-3117 (10.13.11-11.5) Mattermost Plugins versions <=11.5 11.1.5 10.13.11 11.3.4.0 fail to properly check for permissions when processing commands in the Gitlab plugin which allows normal users to uninstall instances or setup webhook connections via the {{gitlab instance {option}}} or the {{/gitlab webhook {option}}} commands. Mattermost Advisory ID: MMSA-2026-00600	Mattermost
CVE-2026-4286	May 18, 2026	Mattermost <=11.5.1 & 10.11.13 Playbook Team ID Bypass via PUT API Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to check if {{team_id}} 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: MMSA-2025-00552	Mattermost
CVE-2026-6339	May 18, 2026	Mattermost burnonread reveal endpoint XRequestedWith header flaw (v<11.5.1) 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 Advisory ID: MMSA-2026-00636	Mattermost
CVE-2026-6340	May 18, 2026	7zip Upload Causing Memory Exhaustion in Mattermost 10.11.13, 11.4.3, 11.5.1 Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate 7zip archive structure before processing which allows an authenticated attacker to cause server memory exhaustion and denial of service via uploading a specially crafted 7zip file with excessive folder declarations.. Mattermost Advisory ID: MMSA-2026-00573	Mattermost
CVE-2026-6341	May 18, 2026	API No-Check Group Access Bypass in Mattermost Plugins <=11.5 (CVE-2026-6341) Mattermost Plugins versions <=11.5 11.1.5 10.13.11 11.3.4.0 fail to have API-level checks on which groups the user can create issues or attach comments to which allows a user that is member of multiple groups to create issues to a locked group via direct API requests. Mattermost Advisory ID: MMSA-2026-00602	Mattermost
CVE-2026-6342	May 18, 2026	Mattermost Plugins <=11.5 NS Flaw Allows Subscription to Unwhitelisted Groups Mattermost Plugins versions <=11.5 11.1.5 10.13.11 11.3.4.0 fail to appropriately check for valid namespaces which allows plugin users to create subscriptions to groups that were not whitelisted via creating groups that share the same prefix as a whitelisted group. Mattermost Advisory ID: MMSA-2026-00601	Mattermost
CVE-2026-3495	May 18, 2026	Mattermost <11.5.1/10.11.13: XSS via unescaped config vars in error pages Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to escape some variables that could contain malicious content during error page composition which allows an attacker with access to edit some site configuration to execute some malicious code via injecting some JS as part of those values.. Mattermost Advisory ID: MMSA-2026-00622	Mattermost
CVE-2026-4273	May 18, 2026	Mattermost 10-11.x Token Rotation Bypass via RefreshedToken Reuse Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to validate that the RefreshedToken differs from the original invite token during remote cluster invite confirmation which allows an authenticated attacker to bypass token rotation and reuse the original invite token via sending a crafted invite confirmation with a RefreshedToken matching the original token. Mattermost Advisory ID: MMSA-2026-00575	Mattermost