Overview
CVE-2025-66039 identifies a significant authentication bypass vulnerability affecting the FreePBX Endpoint Manager module. This flaw arises specifically when the module is configured to use “webserver” authentication. Attackers can exploit this condition to gain unauthorized access to a target user’s session simply by providing an arbitrary value within the HTTP Authorization header. This bypass occurs irrespective of valid credentials, effectively allowing an attacker to impersonate a legitimate user and manage telephony endpoints. The vulnerability impacts versions prior to 16.0.44 and 17.0.23 of the FreePBX Endpoint Manager. For further details, refer to CVE-2025-66039 Details.
Technical Details
The core of CVE-2025-66039 lies in a logic error within the FreePBX Endpoint Manager’s authentication mechanism when it operates in “webserver” mode. Under this configuration, the module fails to properly validate the legitimacy of an `Authorization` header. Instead of requiring a valid token or credentials, the system merely checks for the *presence* of an `Authorization` header. An attacker can craft a request to the vulnerable FreePBX instance, including an `Authorization` header with any non-empty string as its value. Upon receiving such a request, the FreePBX Endpoint Manager incorrectly associates a session with the specified target user, granting the attacker full access to that user’s Endpoint Manager interface. This bypass allows for complete control over managed telephony devices, including configuration changes, firmware updates, and potentially the ability to redirect or intercept calls, depending on the compromised user’s privileges. The attack requires minimal technical sophistication, making it a high-impact vulnerability for affected systems. The simplicity of this attack vector means that even less sophisticated attackers could potentially exploit this flaw, posing a significant risk to the integrity and confidentiality of communication managed by the FreePBX system. Exploitation does not require prior authentication or complex network conditions, further lowering the barrier to entry for malicious actors.
Affected Systems
This vulnerability exclusively impacts installations of the FreePBX Endpoint Manager module. Specifically, all versions of the module prior to 16.0.44 and 17.0.23 are vulnerable. It is crucial to note that the vulnerability is only exploitable when the Endpoint Manager’s authentication type is explicitly set to “webserver.” Systems using other authentication methods are not susceptible to this particular bypass.
Remediation
Organizations managing FreePBX deployments must prioritize patching the Endpoint Manager module. The primary remediation involves upgrading to a secure version.
- For FreePBX Endpoint Manager 16.x, upgrade to version 16.0.44 or newer.
- For FreePBX Endpoint Manager 17.x, upgrade to version 17.0.23 or newer.
If immediate patching is not feasible, a critical interim mitigation is to reconfigure the Endpoint Manager’s authentication type. System administrators should change the authentication type from “webserver” to a more robust and secure method until the module can be fully updated. Additionally, regularly reviewing FreePBX security configurations and applying all available patches promptly remains a fundamental best practice for maintaining a secure telephony environment. Administrators should also conduct a thorough audit of their FreePBX configurations to identify any instances where “webserver” authentication is currently in use for the Endpoint Manager, even if the module itself is up to date, to ensure no legacy configurations pose a risk. Proactive security measures, including regular vulnerability scanning and penetration testing, are highly recommended to identify and address potential weaknesses before they can be exploited.
