CVE-2013-6696 in ASA
Summary
by MITRE
Cisco Adaptive Security Appliance (ASA) Software does not properly handle errors during the processing of DNS responses, which allows remote attackers to cause a denial of service (device reload) via a malformed response, aka Bug ID CSCuj28861.
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Analysis
by VulDB Data Team • 05/16/2017
The vulnerability identified as CVE-2013-6696 affects Cisco Adaptive Security Appliance (ASA) Software versions 8.2 before 8.2(5.30), 8.3 before 8.3(2.20), 8.4 before 8.4(1.20), 8.5 before 8.5(1.20), and 8.6 before 8.6(1.20). This issue stems from inadequate error handling mechanisms within the DNS response processing functionality of the ASA software. The flaw specifically manifests when the device encounters malformed DNS responses during normal network operations, particularly in environments where DNS resolution is actively utilized for various security policies and network services.
The technical root cause of this vulnerability resides in the improper handling of error conditions during DNS response processing within the ASA's network security infrastructure. When the ASA receives a malformed DNS response that does not conform to standard DNS protocol specifications, the device fails to gracefully manage this error condition. Instead of logging the anomaly and continuing normal operations, the software enters an unstable state that ultimately leads to a complete device reload or system crash. This behavior represents a classic buffer overflow or exception handling flaw that falls under the CWE-248 category of "Uncaught Exception" and can be classified as a denial of service vulnerability according to CWE-400.
The operational impact of CVE-2013-6696 extends beyond simple service disruption, as it can compromise the availability of critical network security services provided by the ASA appliance. Network administrators relying on ASA devices for firewall protection, intrusion prevention, and secure remote access may experience complete service outages when this vulnerability is exploited. The attack vector is particularly concerning because it requires no authentication or privileged access, making it accessible to remote attackers who can simply send malformed DNS responses to trigger the device reload. This vulnerability aligns with ATT&CK technique T1499.004 for "Network Denial of Service" and demonstrates how seemingly benign network protocols can be weaponized to disrupt critical infrastructure.
Mitigation strategies for this vulnerability include immediate deployment of Cisco's security advisories and software updates that address the specific error handling flaw in DNS response processing. Organizations should prioritize patching affected ASA devices to versions that contain proper error handling mechanisms for malformed DNS responses. Additionally, network administrators can implement additional monitoring and logging to detect unusual DNS traffic patterns that might indicate exploitation attempts. The vulnerability also highlights the importance of proper input validation and error handling in network security appliances, as recommended by the OWASP Top Ten and NIST Cybersecurity Framework. Network segmentation and the implementation of DNS filtering mechanisms can serve as additional defensive measures while patches are deployed, ensuring continued network availability and security posture maintenance.