CVE-2025-66039 in FreePBX
Summary
by MITRE • 12/10/2025
FreePBX Endpoint Manager is a module for managing telephony endpoints in FreePBX systems. Versions are vulnerable to authentication bypass when the authentication type is set to "webserver." When providing an Authorization header with an arbitrary value, a session is associated with the target user regardless of valid credentials. This issue is fixed in versions 16.0.44 and 17.0.23.
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Analysis
by VulDB Data Team • 02/02/2026
The vulnerability identified as CVE-2025-66039 affects the FreePBX Endpoint Manager module, which serves as a critical component for managing telephony endpoints within FreePBX systems. This module operates within a broader telephony infrastructure that handles voice communications, call routing, and endpoint configuration. The vulnerability specifically manifests when the authentication type is configured to "webserver" mode, a common setting in many FreePBX deployments that relies on external web server authentication mechanisms. This configuration approach is often used to integrate FreePBX with existing authentication systems such as LDAP or Active Directory, but it introduces a significant security flaw when properly implemented.
The technical flaw in this vulnerability stems from improper session handling within the authentication process. When the authentication type is set to "webserver," the system should validate credentials through the external web server before establishing a session. However, the flaw allows an attacker to bypass this validation by simply providing an Authorization header with any arbitrary value. This header-based bypass results in the system creating a session association with the target user account without requiring legitimate authentication credentials. The vulnerability essentially eliminates the authentication check entirely, allowing unauthorized access to the system with the privileges of the targeted user. This type of flaw is categorized under CWE-287, which addresses improper authentication issues, and represents a critical weakness in the authentication mechanism that undermines the security model of the entire system.
The operational impact of this vulnerability is severe and multifaceted, as it provides attackers with unauthorized access to telephony management functions. Once an attacker successfully bypasses authentication, they can perform any action available to the targeted user, including modifying endpoint configurations, creating new users, changing passwords, and potentially accessing sensitive communication data. The vulnerability is particularly dangerous because it can be exploited remotely without requiring prior knowledge of valid credentials, making it an attractive target for automated attacks. The impact extends beyond simple unauthorized access, as the compromised system can be used as a pivot point for further attacks within the network, potentially leading to complete system compromise. According to ATT&CK framework, this vulnerability maps to T1078.004 (Valid Accounts: Web Application Accounts) and T1566.001 (Phishing: Spearphishing Attachment), as it allows for unauthorized access through web application interfaces and can be leveraged for privilege escalation attacks.
Mitigation strategies for this vulnerability should focus on immediate remediation through version updates, as the issue has been resolved in FreePBX versions 16.0.44 and 17.0.23. Organizations should prioritize updating their FreePBX systems to these patched versions to eliminate the authentication bypass vulnerability. Additionally, network administrators should implement monitoring for unauthorized authentication attempts and suspicious Authorization header usage patterns. The configuration should be reviewed to ensure that authentication mechanisms are properly enforced, and alternative authentication methods such as database-based authentication should be considered if webserver authentication cannot be properly secured. Security teams should also conduct thorough audits of all FreePBX installations to identify any other potentially affected systems and ensure that proper access controls are in place to prevent unauthorized modifications to telephony configurations.