CVE-2019-1695 in ASA
Summary
by MITRE
A vulnerability in the detection engine of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, adjacent attacker to send data directly to the kernel of an affected device. The vulnerability exists because the software improperly filters Ethernet frames sent to an affected device. An attacker could exploit this vulnerability by sending crafted packets to the management interface of an affected device. A successful exploit could allow the attacker to bypass the Layer 2 (L2) filters and send data directly to the kernel of the affected device. A malicious frame successfully delivered would make the target device generate a specific syslog entry.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 09/12/2023
The vulnerability identified as CVE-2019-1695 represents a critical security flaw in Cisco's Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD) software implementations. This weakness resides within the detection engine's handling of Ethernet frame processing, creating a pathway for unauthorized kernel-level access that fundamentally undermines the device's security posture. The vulnerability specifically targets the Layer 2 filtering mechanisms that are designed to protect the kernel from malicious traffic originating from the network interface. According to CWE-20, this vulnerability stems from improper input validation and filtering of network frames, where the software fails to adequately sanitize or validate incoming Ethernet traffic before processing it at the kernel level.
The attack vector for CVE-2019-1695 requires an adjacent attacker who can directly communicate with the management interface of an affected device, making this vulnerability particularly dangerous in environments where physical or logical network proximity can be achieved. This adjacency requirement aligns with ATT&CK technique T1046, which describes the use of network service scanning to identify accessible interfaces and ports. The exploitation process involves crafting specifically formatted packets that bypass the normal Layer 2 filtering mechanisms, allowing malicious frames to reach the kernel directly without proper validation. This bypass mechanism creates a direct pathway for privilege escalation and kernel-level manipulation that could enable attackers to execute arbitrary code or access sensitive system resources.
The operational impact of this vulnerability extends beyond simple network access disruption, as successful exploitation could result in complete system compromise and unauthorized access to critical network infrastructure. The syslog entries generated by malicious frame delivery serve as both an indicator of compromise and a potential attack fingerprint that could aid in forensic analysis. The vulnerability affects both ASA and FTD software versions, indicating a widespread impact across Cisco's security product line that includes devices ranging from small branch office appliances to enterprise-grade threat defense systems. Network administrators face significant challenges in identifying and mitigating this vulnerability since the attack can occur through legitimate management interfaces, making it difficult to distinguish between normal operational traffic and malicious activity.
Mitigation strategies for CVE-2019-1695 should focus on implementing network segmentation to prevent adjacent access to management interfaces, applying the latest security patches provided by Cisco, and configuring additional access controls to restrict management interface access. The vulnerability demonstrates the importance of proper input validation and filtering at all network layers, particularly at the kernel interface where such bypasses could have catastrophic consequences. Organizations should also consider implementing network monitoring solutions that can detect unusual syslog patterns or traffic behavior that might indicate exploitation attempts. The incident highlights the critical need for robust Layer 2 security controls and the necessity of maintaining up-to-date security configurations across all network defense systems to prevent similar vulnerabilities from being exploited in operational environments.