CVE-2006-3122 in DHCP
Summary
by MITRE
The supersede_lease function in memory.c in ISC DHCP (dhcpd) server 2.0pl5 allows remote attackers to cause a denial of service (application crash) via a DHCPDISCOVER packet with a 32 byte client-identifier, which causes the packet to be interpreted as a corrupt uid and causes the server to exit with "corrupt lease uid."
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Analysis
by VulDB Data Team • 06/24/2019
The vulnerability identified as CVE-2006-3122 affects the Internet Systems Consortium DHCP server implementation known as dhcpd version 2.0pl5. This issue resides within the supersede_lease function located in the memory.c source file, representing a critical flaw that can be exploited remotely to disrupt service availability. The vulnerability specifically targets the handling of DHCPDISCOVER packets when they contain a 32-byte client-identifier field, creating a scenario where legitimate network traffic can be leveraged to crash the DHCP server process.
The technical mechanism behind this vulnerability involves improper validation of client identifier fields during DHCP lease processing. When a DHCPDISCOVER packet is received with a 32-byte client-identifier, the dhcpd server incorrectly interprets this data as a corrupt user identifier or uid field. This misinterpretation occurs because the server's memory management function fails to properly validate the length and format of client identifiers before processing them. The function attempts to handle this malformed data without proper bounds checking or input sanitization, leading to memory corruption that ultimately causes the server application to terminate abruptly with the error message "corrupt lease uid." This behavior constitutes a classic buffer overflow scenario where insufficient input validation leads to application instability.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise network infrastructure reliability. A remote attacker can exploit this weakness by simply sending a specially crafted DHCPDISCOVER packet, requiring no authentication or privileged access to the network. The resulting denial of service affects the entire DHCP service, preventing legitimate clients from obtaining IP address assignments and potentially disrupting network connectivity for all devices relying on that DHCP server. This vulnerability is particularly dangerous in enterprise environments where DHCP servers are critical infrastructure components, as it can be exploited to create widespread network outages without significant technical expertise or network access. The attack vector is highly accessible since DHCP servers typically operate on well-known ports and are exposed to network traffic from various sources, making them prime targets for this type of denial of service attack.
Mitigation strategies for this vulnerability require immediate implementation of software updates to patched versions of ISC DHCP server that address the memory handling flaw in the supersede_lease function. Organizations should prioritize upgrading to versions that include proper input validation and bounds checking for client identifier fields, ensuring that the server can gracefully handle malformed DHCP packets without crashing. Network administrators should also implement DHCP filtering mechanisms to monitor and potentially block suspicious DHCP traffic patterns, though this approach provides only partial protection since the vulnerability can be triggered by legitimate-looking packets. The remediation process should include thorough testing of updated software in controlled environments before deployment to ensure compatibility with existing network configurations. Additionally, organizations should consider implementing redundant DHCP server configurations to provide failover capabilities and reduce the impact of single points of failure. This vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and represents a typical example of how insufficient input validation can lead to application instability and denial of service conditions. From an ATT&CK perspective, this vulnerability maps to the T1499.004 technique involving network denial of service, demonstrating how remote exploitation can be achieved through manipulation of protocol implementations.