Overview
A critical security vulnerability, identified as CVE-2025-12419, has been discovered in Mattermost. This vulnerability affects multiple versions of Mattermost and could allow an attacker with team creation or admin privileges to take over any user account. The flaw lies in the improper validation of OAuth state tokens during OpenID Connect authentication. This blog post provides a detailed analysis of the vulnerability, its potential impact, and the necessary steps to mitigate the risk.
Technical Details
CVE-2025-12419 stems from a flaw in the OAuth completion flow within Mattermost’s OpenID Connect (OIDC) implementation. Specifically, the application fails to adequately validate the state tokens exchanged during the authentication process. An attacker with sufficient privileges (team creation or admin) can manipulate authentication data during the OAuth completion flow. By crafting malicious authentication requests, they can impersonate another user and gain unauthorized access to their account.
The affected Mattermost versions are:
- 10.12.x <= 10.12.1
- 10.11.x <= 10.11.4
- 10.5.x <= 10.5.12
- 11.0.x <= 11.0.3
CVSS Analysis
The Common Vulnerability Scoring System (CVSS) has assigned a score of 9.9 to CVE-2025-12419, indicating a CRITICAL severity. This high score reflects the potential for complete system compromise and the ease with which the vulnerability can be exploited.
A CVSS score of 9.9 indicates a high probability of exploitation, a low attack complexity, no required privileges (other than those outlined above), and a significant impact on confidentiality, integrity, and availability.
Possible Impact
The exploitation of CVE-2025-12419 can lead to severe consequences, including:
- Account Takeover: Attackers can gain complete control over user accounts, including administrative accounts.
- Data Breach: Access to sensitive data stored within Mattermost.
- Reputation Damage: Loss of trust from users and stakeholders due to a security breach.
- Unauthorized Access: Attackers can use compromised accounts to access other systems and resources connected to the Mattermost environment.
- Lateral Movement: Attackers might leverage compromised Mattermost accounts to gain a foothold and move laterally within the organization’s network.
Mitigation and Patch Steps
The most effective way to mitigate CVE-2025-12419 is to upgrade to a patched version of Mattermost. If upgrading is not immediately possible, consider the following temporary mitigation steps:
- Upgrade Mattermost: Upgrade to the latest available version of Mattermost that includes the security patch for CVE-2025-12419. Check the Mattermost website for the latest releases.
- Review User Privileges: Carefully review and restrict team creation and admin privileges to only those users who absolutely require them. Limiting these privileges reduces the attack surface.
- Monitor Authentication Logs: Closely monitor Mattermost authentication logs for any suspicious activity or unusual patterns.
