CVE-2017-3793 in ASA
Summary
by MITRE
A vulnerability in the TCP normalizer of Cisco Adaptive Security Appliance (ASA) Software (8.0 through 8.7 and 9.0 through 9.6) and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause Cisco ASA and FTD to drop any further incoming traffic on all interfaces, resulting in a denial of service (DoS) condition. The vulnerability is due to improper limitation of the global out-of-order TCP queue for specific block sizes. An attacker could exploit this vulnerability by sending a large number of unique permitted TCP connections with out-of-order segments. An exploit could allow the attacker to exhaust available blocks in the global out-of-order TCP queue, causing the dropping of any further incoming traffic on all interfaces and resulting in a DoS condition. Cisco Bug IDs: CSCvb46321.
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Analysis
by VulDB Data Team • 08/28/2024
The vulnerability identified as CVE-2017-3793 represents a critical denial of service weakness affecting Cisco Adaptive Security Appliance (ASA) and Cisco Firepower Threat Defense (FTD) systems. This flaw resides within the TCP normalizer component of these security appliances, specifically impacting software versions ranging from 8.0 through 8.7 and 9.0 through 9.6. The vulnerability stems from inadequate management of the global out-of-order TCP queue, creating a scenario where an attacker can manipulate the system's resource allocation to achieve a complete service disruption. The TCP normalizer is responsible for handling TCP segments that arrive out of sequence, and this particular weakness allows malicious actors to exhaust the system's available resources through carefully crafted TCP connection sequences.
The technical exploitation mechanism involves sending a substantial volume of unique TCP connections that contain out-of-order segments, specifically targeting the global out-of-order TCP queue with particular block sizes. This targeted approach allows attackers to systematically consume all available blocks within the queue structure, effectively starving the system of the resources needed to process legitimate incoming traffic. The vulnerability is classified under CWE-400 as an unspecified vulnerability in resource management, specifically concerning improper limitation of a resource. The flaw operates at the network protocol level, leveraging the fundamental TCP connection handling mechanisms to create a cascading failure condition that affects all network interfaces on the affected appliance.
The operational impact of this vulnerability extends beyond simple service interruption, as it creates a complete network denial of service condition that affects all interfaces of the compromised appliance. When the global out-of-order TCP queue becomes exhausted, the system ceases to process any further incoming traffic, effectively rendering the security appliance ineffective for its primary function of network protection. This condition can be particularly devastating in enterprise environments where ASA and FTD appliances serve as critical network security gateways, potentially disrupting business operations and leaving networks vulnerable to other threats. The remote nature of the attack means that an unauthenticated attacker can exploit this vulnerability from outside the network perimeter, making it especially dangerous for organizations with exposed security appliances.
Mitigation strategies for CVE-2017-3793 primarily focus on applying the relevant security patches provided by Cisco, which address the improper limitation of the global out-of-order TCP queue. Organizations should prioritize immediate patch deployment across all affected Cisco ASA and FTD systems, following Cisco's recommended upgrade procedures to ensure complete remediation. Network administrators can also implement temporary workarounds such as configuring rate limiting for TCP connections and adjusting TCP queue parameters to reduce the system's susceptibility to this specific attack pattern. The mitigation approach aligns with ATT&CK technique T1499.004 for network denial of service, where adversaries exploit system resource exhaustion to prevent legitimate network access. Additionally, implementing monitoring solutions that can detect unusual TCP connection patterns and queue exhaustion behaviors provides early warning capabilities for potential exploitation attempts.