CVE-2026-22545: Mattermost Auth Bypass Vulnerability

CVE-2026-22545 Overview

CVE-2026-22545 is an authorization bypass vulnerability in Mattermost Server that affects versions 10.11.x <= 10.11.10. The vulnerability stems from a failure to properly validate a user's authentication method when processing account authentication type switch requests. This flaw allows an authenticated attacker to change their account password without the required confirmation by falsely claiming a different authentication provider.

Critical Impact

Authenticated attackers can bypass password confirmation requirements by exploiting the authentication method validation flaw, potentially gaining unauthorized persistent access to Mattermost accounts.

Affected Products

• Mattermost Server versions 10.11.x through 10.11.10

Discovery Timeline

• March 16, 2026 - CVE-2026-22545 published to NVD
• March 18, 2026 - Last updated in NVD database

Technical Details for CVE-2026-22545

Vulnerability Analysis

This vulnerability is classified under CWE-863 (Incorrect Authorization). The core issue lies in Mattermost's account authentication switching functionality, which fails to properly verify the user's current authentication method before allowing password changes. When a user attempts to switch authentication providers, the system should validate that the claimed original authentication method matches the user's actual configured method. However, the affected versions do not perform this validation, creating an authorization bypass condition.

The attack requires network access and an authenticated session, but relies on user interaction to complete the exploitation chain. The impact is limited to integrity concerns, as attackers can modify account credentials without proper authorization, though confidentiality and availability are not directly affected.

Root Cause

The root cause is improper authorization checking in the authentication type switch handler. When processing requests to change authentication methods, the Mattermost Server fails to verify that the user's claimed current authentication provider matches their actual configured provider. This allows attackers to bypass the normal password confirmation workflow by spoofing their authentication type.

Attack Vector

The attack is network-based and requires the attacker to have a valid authenticated session on the Mattermost instance. The exploitation flow involves:

1. An authenticated user initiates an authentication type switch request
2. The attacker falsely claims to be using a different authentication provider (e.g., OAuth, SAML, or LDAP)
3. Due to missing validation, the server accepts the false claim
4. The password change proceeds without the normal confirmation requirements
5. The attacker successfully changes the account password

The vulnerability allows persistent account takeover if successfully exploited, as the attacker can lock out the legitimate user by changing their password.

Detection Methods for CVE-2026-22545

Indicators of Compromise

• Unexpected authentication method change events in Mattermost audit logs
• Password change events without corresponding confirmation workflow completions
• Users reporting inability to log in after unexpected credential changes
• Authentication provider switch requests with mismatched provider claims

Detection Strategies

• Monitor Mattermost audit logs for authentication type switch events followed immediately by password changes
• Implement alerting on password changes that bypass the standard confirmation flow
• Review authentication provider claim mismatches in API request logs
• Correlate user session activity with authentication configuration changes

Monitoring Recommendations

• Enable detailed audit logging for all authentication-related events in Mattermost
• Configure alerts for password modification events outside normal user workflows
• Implement anomaly detection for authentication provider switching patterns
• Review Mattermost system console logs regularly for suspicious authentication activities

How to Mitigate CVE-2026-22545

Immediate Actions Required

• Upgrade Mattermost Server to the latest patched version beyond 10.11.10
• Review audit logs for any evidence of exploitation
• Force password resets for any accounts showing suspicious authentication changes
• Notify users to verify their account credentials and authentication settings

Patch Information

Mattermost has released security updates to address this vulnerability. Organizations should consult the Mattermost Security Updates page for the latest patched versions and detailed upgrade instructions. The advisory is tracked as MMSA-2026-00583.

Workarounds

• Implement network-level restrictions to limit access to the Mattermost authentication API endpoints
• Enable multi-factor authentication (MFA) to add an additional layer of protection
• Monitor and alert on authentication configuration changes at the infrastructure level
• Consider temporarily disabling authentication provider switching if not required for operations