CVE-2026-0997: Mattermost Server Auth Bypass Vulnerability

CVE-2026-0997 Overview

CVE-2026-0997 is an authorization bypass vulnerability affecting Mattermost Server and the Mattermost Zoom Plugin. The vulnerability exists due to improper validation of authenticated users when processing requests to the /plugins/zoom/api/v1/channel-preference endpoint. This flaw allows any logged-in user to modify Zoom meeting restrictions for arbitrary channels through crafted API requests, potentially disrupting organizational communication policies and meeting security controls.

Critical Impact

Any authenticated user can manipulate Zoom meeting preferences for channels they do not own or administer, bypassing intended access controls and potentially disrupting communication workflows.

Affected Products

• Mattermost Server versions 11.1.x <= 11.1.2
• Mattermost Server versions 10.11.x <= 10.11.9
• Mattermost Server versions 11.2.x <= 11.2.1
• Mattermost Plugin Zoom versions <= 1.11.0

Discovery Timeline

• 2026-02-16 - CVE-2026-0997 published to NVD
• 2026-02-18 - Last updated in NVD database

Technical Details for CVE-2026-0997

Vulnerability Analysis

This vulnerability is classified under CWE-863 (Incorrect Authorization). The core issue lies in the Mattermost Zoom Plugin's failure to properly validate that the authenticated user making a request to modify channel preferences actually has the necessary permissions to do so.

When a user sends a request to the /plugins/zoom/api/v1/channel-preference API endpoint, the plugin verifies that the user is logged in but fails to check whether that user has administrative rights over the target channel. This broken access control allows any authenticated user within the Mattermost instance to modify Zoom meeting settings for channels they have no authority over.

The vulnerability can be exploited remotely over the network by any user with valid credentials. No user interaction is required beyond crafting malicious API requests. While the impact is limited to integrity (unauthorized modification of settings) with no direct confidentiality breach or denial of service, this flaw could be leveraged to disrupt meeting policies or weaken security controls on sensitive channels.

Root Cause

The root cause of CVE-2026-0997 is the absence of proper authorization checks in the Zoom plugin's channel preference handling logic. The plugin correctly authenticates the user but incorrectly assumes that any authenticated user should be permitted to modify channel-level Zoom preferences. This violates the principle of least privilege and represents a classic broken access control vulnerability where authentication is conflated with authorization.

Attack Vector

An attacker with a standard user account on a Mattermost instance can exploit this vulnerability by sending crafted HTTP requests to the vulnerable API endpoint. The attack flow involves:

1. Authenticating to the Mattermost instance with valid user credentials
2. Identifying target channel IDs (which may be enumerable or known)
3. Sending a POST request to /plugins/zoom/api/v1/channel-preference with the target channel's ID and modified Zoom settings
4. The server processes the request without verifying channel ownership or administrative permissions

The vulnerability affects the network attack vector, requires low complexity to exploit, and demands only low-level privileges (any authenticated user). Since no user interaction is required, an attacker can systematically modify settings across multiple channels.

Detection Methods for CVE-2026-0997

Indicators of Compromise

• Unusual API requests to /plugins/zoom/api/v1/channel-preference from users who are not channel administrators
• Modifications to Zoom meeting preferences on channels where the modifying user lacks administrative privileges
• High volume of channel preference modification requests from a single user account
• Audit log entries showing channel settings changes by non-privileged users

Detection Strategies

• Implement API endpoint monitoring to track all requests to /plugins/zoom/api/v1/channel-preference
• Configure alerting for channel preference modifications where the requesting user is not in the channel admin list
• Review Mattermost audit logs for unexpected Zoom plugin configuration changes
• Deploy application-layer monitoring to detect patterns of unauthorized API access attempts

Monitoring Recommendations

• Enable comprehensive audit logging for all Zoom plugin API interactions
• Monitor for anomalous patterns such as bulk channel preference modifications
• Set up alerts for channel settings changes during off-hours or from unusual IP addresses
• Correlate Zoom plugin activity with user permission levels to identify authorization bypass attempts

How to Mitigate CVE-2026-0997

Immediate Actions Required

• Update Mattermost Server to version 11.1.3, 10.11.10, or 11.2.2 or later (depending on your version branch)
• Update the Mattermost Zoom Plugin to version 1.11.1 or later
• Review audit logs for any signs of exploitation prior to patching
• Verify channel Zoom preferences have not been tampered with on sensitive channels

Patch Information

Mattermost has released security updates addressing this vulnerability as documented in advisory MMSA-2025-00558. Patches are available for all affected version branches. Organizations should prioritize updating to the fixed versions to eliminate this authorization bypass vulnerability. For detailed information on available patches, refer to the Mattermost Security Updates page.

Workarounds

• Restrict network access to the Mattermost instance to trusted users only until patching is complete
• Consider temporarily disabling the Zoom plugin if Zoom integration is not business-critical
• Implement web application firewall rules to restrict access to the vulnerable API endpoint
• Monitor and audit all Zoom plugin API activity more closely pending the application of patches

# Example: Temporarily disable the Zoom plugin via Mattermost CLI
mattermost plugin disable com.mattermost.zoom

# Verify plugin status
mattermost plugin list