CVE-2026-19601 in Mattermost
Summary
by MITRE • 10/16/2026
Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to invalidate the stored AD/LDAP bind password when other connection settings (such as the server address) are changed, which allows a System Console administrator to disclose the plaintext bind password to an attacker-controlled server via the Test Connection / diagnostics feature. Mattermost Advisory ID: MMSA-2026-00764
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Analysis
by VulDB Data Team • 10/16/2026
The vulnerability identified in Mattermost versions 11.9.x through 11.10.1, specifically affecting releases up to 11.9.1, 11.8.5, and 11.7.10, represents a critical security flaw within the platform's Active Directory and LDAP integration mechanisms. This issue stems from an improper handling of stored credentials during configuration changes in the System Console. When an administrator modifies connection parameters such as the server address or port while retaining the existing bind password entry, the system fails to invalidate or clear the previously cached plaintext password before attempting a new connection test. This design oversight creates a scenario where sensitive authentication material is exposed under specific operational conditions involving diagnostic tools.
The technical root cause lies in the logic governing the Test Connection and diagnostics features of the Mattermost System Console. These features are designed to validate connectivity by establishing temporary connections using provided credentials. However, when existing LDAP or AD settings are altered without explicitly resetting the password field, the application reuses the stored plaintext bind password for the new connection attempt. Crucially, during this diagnostic process, if the test fails due to network issues or other configuration errors, the error handling routine may inadvertently log or transmit sensitive details back through standard debugging channels or external request mechanisms intended for diagnostics. This behavior allows an attacker with access to a controlled server endpoint to intercept these transmissions and capture the plaintext bind password in transit or via logs associated with the diagnostic callback.
From an operational impact perspective, this vulnerability poses severe risks to organizational security posture. The exposed LDAP or Active Directory bind account typically possesses read-only permissions but often has broad visibility into user directories, including usernames, email addresses, group memberships, and potentially other sensitive attributes depending on directory policies. If an attacker obtains these credentials, they can perform extensive reconnaissance against the organization's identity infrastructure. This information is highly valuable for crafting targeted phishing campaigns or social engineering attacks aimed at privileged users. Furthermore, if the bind account has been misconfigured with write permissions, which violates least privilege principles but occurs in some environments, the attacker could potentially modify user attributes, reset passwords, or create unauthorized accounts to maintain persistent access within the organization's network perimeter.
This vulnerability aligns closely with CWE-259, Use of Hard-coded Passwords, and more specifically CWE-798, Use of Hard-coded Credentials, as it involves the improper handling and exposure of stored secrets rather than static hardcoding in source code. It also relates to CWE-319, Cleartext Transmission of Sensitive Information, given that the password is transmitted or logged during diagnostic operations without adequate protection. In terms of adversary tactics, this flaw facilitates reconnaissance activities consistent with MITRE ATT&CK technique T1087, Account Discovery, and potentially T1528, Steal Application Access Token, depending on how the captured credentials are leveraged for subsequent lateral movement or privilege escalation within the identity management ecosystem.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. The primary defense is to apply the vendor-provided patches immediately to update Mattermost installations to versions where this flaw has been addressed, ensuring that bind passwords are properly invalidated when connection settings change. Administrators should also enforce strict least privilege principles by configuring LDAP/AD bind accounts with minimal necessary permissions, ideally read-only access restricted to specific organizational units rather than the entire directory tree. Additionally, organizations should implement network segmentation and monitoring to detect unusual outbound connections from Mattermost servers that might indicate exploitation of this diagnostic feature. Regular auditing of System Console configurations and disabling unnecessary diagnostic features in production environments can further reduce the attack surface associated with credential exposure during administrative tasks.