CVE-2019-12673 in ASA
Summary
by MITRE
A vulnerability in the FTP inspection engine of Cisco Adaptive Security (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability is due to insufficient validation of FTP data. An attacker could exploit this vulnerability by sending malicious FTP traffic through an affected device. A successful exploit could allow the attacker to cause a DoS condition on the affected device.
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Analysis
by VulDB Data Team • 12/29/2023
The vulnerability identified as CVE-2019-12673 resides within the FTP inspection engine of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software, representing a critical security flaw that compromises the availability of network infrastructure devices. This weakness specifically targets the protocol inspection capabilities that monitor and validate FTP traffic passing through affected Cisco security appliances, creating a potential entry point for malicious actors seeking to disrupt network operations. The flaw manifests in the insufficient validation mechanisms applied to FTP data streams, which are processed by the software's inspection engine designed to monitor and control file transfer protocols.
The technical implementation of this vulnerability stems from inadequate input validation within the FTP protocol handling subsystem of Cisco's security solutions. When the affected software processes FTP data connections, it fails to properly validate the structure and content of FTP commands and responses, particularly those related to data transfer operations. This validation gap allows maliciously crafted FTP traffic to bypass normal inspection procedures and potentially trigger unexpected behavior within the software's processing engine. The vulnerability specifically impacts the FTP inspection engine's ability to handle malformed or specially crafted FTP data sequences, which can cause the software to enter an unstable state or terminate critical processes.
Operationally, this vulnerability creates a significant risk for organizations relying on Cisco ASA and FTD devices for network security protection, as it enables unauthenticated remote attackers to induce denial of service conditions without requiring any credentials or privileged access. The exploit requires only the ability to send malicious FTP traffic through the affected device, making it particularly dangerous as it can be leveraged by attackers from outside the network perimeter. Successful exploitation results in the affected device becoming unavailable to legitimate users, potentially disrupting critical business operations and network connectivity. The DoS condition can persist until manual intervention occurs, requiring administrators to restart the affected security appliance or apply software patches.
Organizations should implement immediate mitigations including applying the latest security patches provided by Cisco, which address the validation deficiencies in the FTP inspection engine. Network segmentation strategies can help limit the attack surface by restricting FTP traffic to necessary network segments. Monitoring for unusual FTP traffic patterns and implementing intrusion detection systems can help detect exploitation attempts before they succeed. The vulnerability aligns with CWE-20, "Improper Input Validation," and represents a specific implementation weakness in protocol handling that can be categorized under ATT&CK technique T1499.004, "Endpoint Denial of Service," demonstrating how inadequate protocol validation can lead to service disruption attacks. Security teams should also consider implementing temporary network access controls that restrict FTP traffic until permanent patches are deployed across all affected devices.