CVE-2015-6324 in ASA
Summary
by MITRE
The DHCPv6 relay implementation in Cisco Adaptive Security Appliance (ASA) software 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(2) allows remote attackers to cause a denial of service (device reload) via crafted DHCPv6 packets, aka Bug IDs CSCus56252 and CSCus57142.
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Analysis
by VulDB Data Team • 11/18/2024
The vulnerability described in CVE-2015-6324 represents a critical denial of service flaw within the DHCPv6 relay functionality of Cisco Adaptive Security Appliance software versions prior to specific patch releases. This issue affects multiple major versions including 9.0 through 9.4, creating a widespread impact across enterprise network security infrastructure. The flaw manifests when the ASA device processes malformed or specially crafted DHCPv6 packets, leading to unexpected device behavior and ultimately complete system reload. The vulnerability specifically targets the DHCPv6 relay implementation which serves as a critical component for forwarding DHCPv6 traffic between clients and servers across different network segments, making it a prime target for attackers seeking to disrupt network operations.
The technical mechanism behind this vulnerability involves improper input validation within the DHCPv6 packet processing logic of the ASA software. When the system receives specially crafted DHCPv6 packets containing malformed options or unexpected packet structures, the relay implementation fails to properly handle these edge cases, resulting in a memory corruption condition or stack overflow that triggers the device to automatically reboot. This type of vulnerability falls under CWE-121, which describes stack-based buffer overflow conditions, and CWE-122, which covers heap-based buffer overflow scenarios. The attack vector requires only network access to send malicious DHCPv6 packets to the affected ASA device, making it particularly dangerous as it can be exploited from remote locations without requiring physical access or authentication credentials.
The operational impact of this vulnerability extends far beyond simple service disruption, as it can effectively disable critical network security functions provided by the ASA appliance. When an ASA device experiences a reload due to this vulnerability, it temporarily removes all network traffic filtering, access control, and security policies that the device was enforcing, creating a window of vulnerability where network traffic flows unrestricted. This disruption can affect entire network segments, potentially allowing unauthorized access to sensitive resources while the device is offline. The attack can be particularly devastating in environments where the ASA serves as a primary security gateway, as the device reload may take several minutes to complete, during which time the network is left exposed to potential threats.
Organizations affected by this vulnerability should immediately implement mitigation strategies to protect their network infrastructure. The primary recommendation involves applying the vendor-supplied patches and software updates that address the specific DHCPv6 relay processing flaws. Cisco released multiple software releases including 9.0(4.37), 9.1(6.6), 9.2(4), 9.3(3.5), and 9.4(2) to resolve this issue. Network administrators should also consider implementing additional protective measures such as rate limiting for DHCPv6 traffic, implementing ACLs to restrict DHCPv6 packet sources, and monitoring network traffic for unusual DHCPv6 packet patterns that might indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability aligns with technique T1499.002 which covers network denial of service attacks, and T1566.002 which involves spearphishing through social engineering. The vulnerability also represents a significant concern for compliance frameworks such as NIST SP 800-53 and ISO 27001, where maintaining system availability and preventing unauthorized access are critical control objectives.