CVE-2017-7937 in mGuard
Summary
by MITRE
An Improper Authentication issue was discovered in Phoenix Contact GmbH mGuard firmware versions 8.3.0 to 8.4.2. An attacker may be able to gain unauthorized access to the user firewall when RADIUS servers are unreachable.
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Analysis
by VulDB Data Team • 09/30/2020
The vulnerability identified as CVE-2017-7937 represents a critical authentication flaw in the mGuard firewall firmware produced by Phoenix Contact GmbH. This weakness exists within firmware versions ranging from 8.3.0 through 8.4.2, creating a significant security risk for organizations relying on this network protection infrastructure. The flaw specifically manifests when RADIUS servers become unreachable, allowing unauthorized access to the user firewall through improper authentication mechanisms. This issue directly impacts the integrity of the authentication process that should normally validate user credentials through external RADIUS servers before granting access to network resources.
The technical nature of this vulnerability stems from the firmware's failure to properly handle authentication failures when external RADIUS servers are unavailable. When RADIUS servers cannot be reached due to network issues, connectivity problems, or server failures, the mGuard firmware should maintain secure authentication policies and deny access to unauthorized users. However, the flawed implementation allows the system to potentially grant access without proper authentication, creating a persistent security gap. This behavior violates fundamental security principles and represents a clear deviation from expected authentication protocols. The vulnerability operates at the authentication layer of the network security infrastructure, where proper credential validation should always occur before access permissions are granted. The flaw essentially creates a fallback mechanism that bypasses normal security controls when primary authentication servers are unreachable, which constitutes a serious design oversight in the firmware's security architecture.
The operational impact of this vulnerability extends beyond simple unauthorized access to potentially compromise entire network infrastructures. Organizations utilizing affected mGuard firmware versions face significant risks when their RADIUS servers experience temporary outages or become unreachable due to network disruptions. Attackers could exploit this weakness during maintenance windows, network failures, or even through targeted denial-of-service attacks aimed at disabling RADIUS connectivity. The vulnerability creates a window of opportunity where legitimate network security controls are circumvented, potentially allowing threat actors to establish persistent access to protected networks. This risk is particularly concerning in environments where network security relies heavily on centralized authentication mechanisms, as the failure of these systems could lead to complete bypass of firewall protections. The impact aligns with attack techniques described in the mitre ATT&CK framework under credential access and privilege escalation categories, where unauthorized access to network devices can lead to broader system compromise.
Security mitigations for this vulnerability should prioritize immediate firmware updates to versions that address the authentication flaw, as provided by Phoenix Contact GmbH. Organizations should implement network monitoring to detect and alert on RADIUS server connectivity issues, as these events may indicate potential exploitation attempts. Network segmentation and additional access controls should be implemented to limit the potential impact of unauthorized access even when the primary authentication mechanism fails. Regular security assessments of network infrastructure should include verification of authentication server reachability and proper fallback mechanism configurations. The vulnerability demonstrates the importance of proper fallback authentication design and aligns with CWE categories related to improper authentication and security misconfiguration. Organizations should also consider implementing redundant authentication systems and maintaining detailed logs of authentication events to detect potential exploitation attempts. This vulnerability highlights the critical need for robust authentication fail-safe mechanisms that prevent security controls from being bypassed during system failures, as outlined in industry standards for secure network device implementation.