CVE-2018-0421 in Prime Access Registrar
Summary
by MITRE
A vulnerability in TCP connection management in Cisco Prime Access Registrar could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition when the application unexpectedly restarts. The vulnerability is due to incorrect handling of incoming TCP SYN packets to specific listening ports. The improper handling of the TCP SYN packets could cause a system file description to be allocated and not freed. An attacker could exploit this vulnerability by sending a crafted stream of TCP SYN packets to the application. A successful exploit could allow the attacker to cause the application to eventually restart if a file description cannot be obtained.
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Analysis
by VulDB Data Team • 05/22/2023
The vulnerability identified as CVE-2018-0421 resides within Cisco Prime Access Registrar's TCP connection management mechanisms, representing a critical weakness that enables remote unauthenticated attackers to induce denial of service conditions. This flaw specifically targets the application's handling of TCP SYN packets directed at designated listening ports, creating a pathway for malicious exploitation that ultimately results in application restarts and service disruption. The vulnerability operates at the network protocol level, leveraging fundamental TCP connection establishment mechanisms to create a resource exhaustion scenario that compromises system availability.
The technical root cause of this vulnerability stems from improper memory management practices within the TCP connection handling code path. When the application receives TCP SYN packets, it allocates system file description structures to manage incoming connections, but fails to properly release these allocations when processing malformed or crafted packets. This memory leak occurs because the system does not adequately validate or process certain TCP SYN packet sequences that trigger the allocation of file descriptors without corresponding deallocation. The issue manifests as a gradual accumulation of unreleased file descriptors that eventually exhaust system resources, leading to application instability and forced restarts. This behavior aligns with CWE-404, which addresses improper resource management and memory leaks in software systems.
The operational impact of this vulnerability extends beyond simple service disruption to encompass potential business continuity implications for organizations relying on Cisco Prime Access Registrar for network access control and authentication services. Attackers can exploit this weakness through network-based means without requiring authentication credentials, making the attack surface particularly broad and accessible. The vulnerability's exploitation requires only the transmission of specially crafted TCP SYN packets to targeted listening ports, making it relatively simple to implement and potentially scalable across multiple systems. When successfully exploited, the vulnerability creates a cascading effect where system resources become exhausted, forcing the application to restart and potentially disrupting network access for legitimate users. This DoS condition can persist until manual intervention occurs or the system automatically recovers from resource exhaustion.
Mitigation strategies for CVE-2018-0421 should prioritize immediate patch deployment from Cisco, as the vendor has released security updates addressing the specific memory management flaws in the TCP connection handling code. Network administrators should implement perimeter filtering rules to restrict access to vulnerable listening ports, particularly those associated with TCP services that are not externally exposed. The implementation of rate limiting mechanisms and SYN flood protection measures can help reduce the effectiveness of exploitation attempts by limiting the volume of TCP SYN packets that can be processed within a given timeframe. Organizations should also consider implementing monitoring solutions that can detect unusual patterns in file descriptor usage or system restarts that may indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability maps to technique T1499.004, which involves network denial of service attacks, and T1566.001, covering spearphishing via social media, as attackers may use this vulnerability to target specific organizations. The vulnerability's classification as a resource exhaustion issue also aligns with defense-in-depth strategies that emphasize proper resource management and robust error handling in network services.