CVE-2015-6326 in ASA
Summary
by MITRE
Cisco Adaptive Security Appliance (ASA) software 7.2 and 8.2 before 8.2(5.58), 8.3 and 8.4 before 8.4(7.29), 8.5 through 8.7 before 8.7(1.17), 9.0 before 9.0(4.37), 9.1 before 9.1(6.6), 9.2 before 9.2(4), 9.3 before 9.3(3.5), and 9.4 before 9.4(1.5) allows remote attackers to cause a denial of service (device reload) via a crafted DNS response, aka Bug ID CSCuu07799.
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Analysis
by VulDB Data Team • 11/18/2024
The vulnerability described in CVE-2015-6326 represents a critical denial of service flaw within Cisco Adaptive Security Appliance software versions spanning multiple release lines from 7.2 through 9.4. This weakness specifically targets the device's handling of DNS responses, creating a scenario where remote attackers can manipulate the ASA system into performing an unintended device reload operation. The vulnerability affects a broad range of ASA software versions, with specific patches required for each major release line including 8.2, 8.3, 8.4, 8.5, 8.7, 9.0, 9.1, 9.2, 9.3, and 9.4, demonstrating the widespread nature of the issue across Cisco's security appliance portfolio. The flaw resides in the ASA's DNS processing mechanism where malformed or crafted DNS responses can trigger an abnormal system state leading to complete device restart.
The technical implementation of this vulnerability involves the manipulation of DNS response packets that the ASA device receives and processes. When the appliance encounters a specially crafted DNS response, it fails to properly validate or handle the packet structure, causing an internal error that results in a system crash and subsequent automatic reload of the device. This behavior aligns with CWE-129, which describes improper validation of input ranges, and specifically relates to improper handling of malformed network packets within security appliances. The vulnerability is particularly dangerous because it can be exploited remotely without requiring authentication, making it accessible to any attacker who can intercept network traffic or manipulate DNS responses through techniques such as DNS cache poisoning or man-in-the-middle attacks. The attack vector leverages the fundamental DNS resolution process that ASA devices use to communicate with external systems, making it a core component of the appliance's normal operations.
The operational impact of CVE-2015-6326 extends far beyond simple service disruption, as device reloads can result in complete network outages for organizations relying on ASA for network security. During the reload process, all active connections are terminated and network traffic is temporarily blocked, creating a window of vulnerability that can be exploited by malicious actors. This disruption can have cascading effects throughout enterprise networks, particularly in environments where ASA devices serve as primary firewalls, NAT gateways, or VPN termination points. The vulnerability's remote exploitability means that attackers can target multiple devices simultaneously, potentially causing widespread network disruption across organizations. From an attacker perspective, this flaw maps to ATT&CK technique T1499.004, which describes network disruption through service availability, and represents a significant threat to network availability and business continuity. Organizations using affected ASA versions face the risk of prolonged outages, potential data loss during reload events, and increased exposure to other attacks during the recovery period.
Mitigation strategies for this vulnerability require immediate implementation of software patches provided by Cisco, with specific release notes indicating the affected versions and corresponding fixes. Organizations should prioritize updating their ASA devices to the patched versions, particularly focusing on the release lines mentioned in the vulnerability description. Network administrators should also implement additional monitoring to detect unusual DNS traffic patterns that might indicate exploitation attempts. The vulnerability's nature suggests that implementing DNS filtering and validation mechanisms can provide additional protection layers, though the most effective defense remains timely patch management. Organizations should also consider implementing network segmentation to limit the potential impact of exploitation and establish incident response procedures to quickly address any attempted exploitation. The remediation process should include thorough testing of patched firmware in non-production environments before deployment to ensure compatibility with existing network configurations and services.