By vendor

Mattermost vulnerabilities

Known CVEs affecting Mattermost products, prioritized by severity, with SEC.co remediation and detection guidance.

17 published vulnerabilities

• CVE-2026-7387HIGH 8.8

  A privilege escalation vulnerability exists in Mattermost that allows users with basic group-link permissions to promote themselves and other group members to team or channel administrator status without proper authorization checks. An attacker could exploit this by sending specially crafted API requests to the group syncable link and patch endpoints, bypassing the role-management authorization layer. This affects multiple versions across Mattermost 11.6, 11.5, and 10.11 release lines.

• CVE-2026-6961HIGH 7.6

  Mattermost has a path traversal vulnerability in how it processes filenames from federated servers during shared channel file synchronization. An attacker controlling a federated Mattermost instance can craft malicious filenames with directory traversal sequences (e.g., ../../../) to write files to unintended locations on a target server's filesystem. This could allow an attacker to overwrite configuration files, inject malicious content, or degrade system availability.

• CVE-2026-6739MEDIUM 6.7

  Mattermost Server has a privilege escalation flaw affecting multiple recent versions (11.6.1, 11.5.4, 10.11.15, and 10.11.16). Users with delegated user-management permissions can abuse the role patch API to modify built-in system roles without proper authorization checks, effectively gaining elevated system privileges they shouldn't possess. An authenticated attacker doesn't need admin status—just user-management delegation—to exploit this, making it a meaningful risk in environments with distributed role administration.

• CVE-2026-4339MEDIUM 6.5

  Mattermost has a flaw in its Agents plugin that fails to block requests to private or internal network addresses. An authenticated attacker with access to the MCP (Model Context Protocol) server in stdio mode can exploit this to retrieve sensitive data from internal services by crafting attachment URLs pointing to internal IP ranges. The vulnerability affects Mattermost versions 10.11.x up to 10.11.18, 11.5.x up to 11.5.6, and 11.6.x up to 11.6.3.

• CVE-2026-7184MEDIUM 6.5

  Mattermost Server contains a flaw in how it processes certain administrative API requests that allows authenticated users with specific permissions to extract security credentials used for remote cluster connections. An attacker with the 'manage_secure_connections' permission can craft a specially designed API request to retrieve authentication tokens that should remain protected. This affects versions 11.6.1 and earlier, 11.5.4 and earlier, and 10.11.15 and earlier.

• CVE-2026-8683MEDIUM 6.5

  Mattermost Desktop App versions 6.1 and earlier contain a denial-of-service vulnerability that allows a malicious server owner to crash the application by injecting a script that attempts to open an extremely long URL. The flaw stems from insufficient validation of URL length before passing it to the browser's window.open function, causing the application to fail ungracefully when processing the oversized input.

• CVE-2026-6062MEDIUM 6.4

  Mattermost Server contains an authorization flaw that allows authenticated users to modify notification subscriptions for channels they don't have access to. An attacker with any valid Mattermost account can craft a specially formed request to edit subscription settings on channels outside their permissions, potentially redirecting notifications or modifying channel monitoring rules. The vulnerability affects multiple versions across the 10.11, 11.5, 11.6, and 11.7 release lines and requires an attacker to already have valid authentication credentials to the Mattermost instance.

• CVE-2026-6673MEDIUM 6.4

  Mattermost is vulnerable to an authentication bypass in how it handles Atlassian Connect integration callbacks. During the window when a Jira integration is being installed, an attacker with valid Mattermost user credentials can craft a malicious POST request to trick the system into accepting a fake shared secret. This compromises the trust relationship between Mattermost and Jira, allowing disruption of the integration and potentially enabling further attacks. The vulnerability affects multiple versions across the 10.11, 11.5, 11.6, and 11.7 release lines.

• CVE-2026-6517MEDIUM 6.3

  Mattermost Desktop App versions 6.1 and earlier contain a credential leakage vulnerability affecting systems without image proxy enabled. When a user opens a message containing an embedded image pointing to an attacker's server, the application automatically forwards the user's NTLM credentials to that external domain. This occurs because the app fails to maintain a strict allowlist of trusted domains for credential forwarding, enabling attackers to harvest authentication material from any user on the server.

• CVE-2026-5139MEDIUM 5.4

  Mattermost has a flaw in how it controls access to GitLab integration settings. Any logged-in user can run a slash command (/gitlab connect) to change which GitLab instance the entire Mattermost workspace uses by default. This should only be allowed for administrators. An attacker with any valid Mattermost account could redirect the workspace to a malicious GitLab instance, potentially capturing credentials or injecting compromised code through pull requests and CI/CD pipelines.

• CVE-2026-6046MEDIUM 5.3

  Mattermost has a vulnerability in its bot registration process that fails to properly verify bot account ownership. An attacker with basic user access can register a standard user account using a name that matches a plugin bot's predictable username. This allows them to intercept private messages intended for that bot—messages that often contain sensitive information passed between plugins and administrators. The vulnerability affects multiple Mattermost versions across the 11.6, 11.5, and 10.11 release lines.

• CVE-2026-3433MEDIUM 4.3

  Mattermost's websocket service inadvertently broadcasts permission change notifications to all authenticated users, including guest-level accounts, even when those users lack membership in the affected team or channel. An attacker with guest credentials can observe role and permission updates for private teams they should have no visibility into, revealing information about organizational access controls. This is a confidentiality issue requiring authentication to exploit but affecting teams that rely on Mattermost's role-based access controls to maintain information barriers between guest and member populations.

• CVE-2026-6689MEDIUM 4.3

  Mattermost has a permissions bypass vulnerability affecting multiple versions where authenticated users with team-creation rights can inappropriately configure invitation settings during team setup. Specifically, users lacking the PermissionInviteUser permission can set AllowOpenInvite (making a team publicly joinable) and AllowedDomains (restricting team membership to specific domains) during POST-based team creation—settings they would normally be blocked from configuring on existing teams. The vulnerability requires an authenticated account and results in unauthorized configuration of team access controls, not data disclosure or system failure.

• CVE-2026-9162MEDIUM 4.3

  Mattermost has a session management flaw affecting versions 11.7.0, 11.6.2 and earlier, 11.5.5 and earlier, and 10.11.17 and earlier. When an administrator revokes a user's global session—such as during offboarding or after detecting unauthorized access—the system fails to immediately disconnect active WebSocket connections used for real-time messaging and notifications. An attacker or departing employee with an existing connection can remain authenticated and continue receiving live team communications until their cached session naturally expires or they manually reconnect. This is a persistence risk in environments where rapid session termination is critical for security or compliance.

• CVE-2026-8074LOW 3.8

  Mattermost has a permission enforcement gap in its user status management API. A User Manager with write access to user management—but explicitly without access to manage integrations or bots—can deactivate bot accounts by directly calling the user active status endpoint. This should not be possible; the API should reject such requests from users lacking bot management permissions. The vulnerability affects Mattermost Server versions 11.7.0 and earlier in the 11.7.x branch, and 10.11.17 and earlier in the 10.11.x branch.

• CVE-2026-8823LOW 3.8

  Mattermost has a permission validation flaw affecting versions 11.7.0 and 10.11.x up to 10.11.17. When an administrator with limited privileges attempts to demote a user to guest status, the system fails to properly verify whether the target is a bot account. This oversight allows a lower-privileged admin to degrade arbitrary bot accounts—including those managed by higher-privileged administrators—through the standard user demotion API. The impact is confined to integrity and availability concerns within the messaging platform.

• CVE-2026-3472LOW 3.5

  Mattermost chat server has a vulnerability where AI bot result posts bypass markdown image rendering restrictions. An authenticated user can craft specially formatted content that, when viewed by a victim in their Mattermost client, triggers image requests to an attacker's server—potentially exfiltrating data about what the victim is viewing. The vulnerability requires a valid Mattermost account and user interaction (clicking or viewing the malicious post), limiting but not eliminating risk in collaborative environments.