CVE-2017-6094 in GAPS
Summary
by MITRE
CPEs used by subscribers on the access network receive their individual configuration settings from a central GAPS instance. A CPE identifies itself by the MAC address of its WAN interface and a certain "chk" value (48bit) derived from the MAC. The algorithm used to compute the "chk" was disclosed by reverse engineering the CPE's firmware. As a result, it is possible to forge valid "chk" values for any given MAC address and therefore receive the configuration settings of other subscribers' CPEs. The configuration settings often contain sensitive values, for example credentials (username/password) for VoIP services. This issue affects Genexis B.V. GAPS up to 7.2.
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Analysis
by VulDB Data Team • 12/21/2017
The vulnerability described in CVE-2017-6094 represents a critical authentication bypass flaw within the Genexis B.V. GAPS system, specifically affecting versions up to 7.2. This issue stems from a fundamental weakness in the method used to generate and validate authentication tokens for customer premises equipment. The system operates on a centralized configuration model where each CPE identifies itself to the GAPS instance through a combination of its MAC address and a 48-bit "chk" value that is derived from this MAC address. The vulnerability arises from the fact that the algorithm used to compute these chk values was reverse-engineered, exposing the underlying mathematical process that generates these authentication tokens. This disclosure effectively undermines the entire authentication mechanism that was designed to ensure only legitimate CPEs could access their respective configuration profiles. The flaw creates a scenario where an attacker with knowledge of the algorithm can generate valid chk values for any MAC address, thereby gaining unauthorized access to configuration data belonging to other subscribers.
The technical exploitation of this vulnerability follows a well-defined pattern that leverages the disclosed algorithm to forge authentication tokens. Since the chk value computation process was reverse-engineered from the CPE firmware, attackers can implement the same algorithm to generate valid tokens for arbitrary MAC addresses. This creates a path for lateral movement within the network infrastructure where unauthorized parties can access configuration settings of other subscribers' devices. The configuration data retrieved through this method often contains highly sensitive information including VoIP service credentials, network access details, and potentially other authentication parameters that could be used for further attacks. The vulnerability directly maps to CWE-287 which addresses improper authentication issues, and the attack pattern aligns with MITRE ATT&CK technique T1078 for valid accounts, as it allows unauthorized access using legitimate authentication tokens that were meant to be unique to specific devices.
The operational impact of this vulnerability extends far beyond simple information disclosure, creating significant risks for network security and subscriber privacy. When attackers can access configuration settings meant for specific subscribers, they gain access to VoIP credentials that could be used for unauthorized calls, potentially leading to financial losses through toll fraud. The compromised configuration data may also reveal network topology information, access credentials for other services, and potentially even administrative access details that could enable more extensive compromise of the network infrastructure. This vulnerability essentially allows attackers to perform subscriber impersonation attacks, where they can masquerade as legitimate network users and access services that should be restricted to specific subscribers. The attack vector is particularly concerning because it does not require physical access to the network or advanced exploitation techniques, making it accessible to threat actors with moderate technical capabilities.
Mitigation strategies for CVE-2017-6094 must address both the immediate vulnerability and the underlying architectural weaknesses that enabled this flaw. Organizations should implement immediate patches or updates to the GAPS system to correct the chk value generation algorithm, ensuring that the computation process is no longer predictable or reversible. Network segmentation and access controls should be strengthened to limit the scope of damage that could occur even if the vulnerability is exploited. Implementing additional authentication layers such as challenge-response mechanisms or time-based token validation would provide defense-in-depth against similar vulnerabilities. Regular security assessments of firmware and embedded systems should be conducted to identify potential reverse-engineering opportunities that could expose critical algorithms. The vulnerability also highlights the importance of protecting proprietary algorithms through proper software engineering practices, including the use of secure coding standards and avoiding predictable mathematical functions in authentication systems. Organizations should also implement monitoring solutions that can detect unusual patterns of configuration access requests that might indicate exploitation attempts. This vulnerability serves as a reminder of the critical importance of secure algorithm design and the need for robust authentication mechanisms in network infrastructure systems, particularly those handling sensitive subscriber information.