CVE-2005-0876 in Dnsmasq
Summary
by MITRE
Off-by-one buffer overflow in Dnsmasq before 2.21 may allow attackers to execute arbitrary code via the DHCP lease file.
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Analysis
by VulDB Data Team • 06/06/2019
The vulnerability identified as CVE-2005-0876 represents a critical buffer overflow condition within the Dnsmasq DNS and DHCP server software. This issue affects versions prior to 2.21 and stems from an off-by-one error in the handling of DHCP lease files. The flaw occurs when the software processes DHCP lease information, specifically during the parsing of lease file entries where insufficient bounds checking is performed on buffer allocations. This type of vulnerability falls under the CWE-121 category of stack-based buffer overflow, though the specific manifestation involves heap memory corruption due to improper memory management during lease file processing. The vulnerability is particularly concerning because it can be exploited remotely through network-based attacks against the DHCP service.
The technical implementation of this vulnerability exploits a fundamental memory management flaw in how Dnsmasq handles lease file entries. When processing DHCP lease information, the software allocates memory buffers based on the size of incoming data without proper validation of the actual data boundaries. An attacker can craft a malicious DHCP lease file entry that exceeds the allocated buffer size by exactly one byte, triggering the off-by-one condition. This allows the attacker to overwrite adjacent memory locations, potentially corrupting critical program state information or function pointers. The attack vector leverages the DHCP service's ability to read and process lease files, which are typically stored on disk and automatically loaded during service initialization. This represents a classic example of a memory safety vulnerability that can be exploited to gain arbitrary code execution privileges on the affected system.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with a potential foothold for broader network compromise. Since Dnsmasq is commonly deployed in network infrastructure devices, routers, and embedded systems, exploitation could lead to complete system compromise and unauthorized network access. The vulnerability is particularly dangerous in environments where DHCP services are automatically configured or where lease files are generated from untrusted sources. Attackers could leverage this flaw to install backdoors, modify network configuration settings, or redirect traffic to malicious endpoints. The exploitability of this vulnerability is enhanced by the fact that it requires minimal privileges to execute and can be triggered through legitimate network operations. This aligns with ATT&CK technique T1059.007 for command and scripting interpreter and T1068 for exploit for privilege escalation, making it a significant threat to network infrastructure security.
Mitigation strategies for CVE-2005-0876 should prioritize immediate software updates to Dnsmasq version 2.21 or later, which contain the necessary patches to address the buffer overflow condition. Organizations should also implement network segmentation and access controls to limit exposure of DHCP services to untrusted networks. Additional protective measures include regular monitoring of DHCP lease files for suspicious entries and implementing automated systems to detect anomalous DHCP behavior patterns. Network administrators should consider disabling unnecessary DHCP functionality when not required and ensure that all systems running Dnsmasq are properly patched and updated according to vendor security advisories. The vulnerability highlights the importance of proper input validation and memory management practices in network infrastructure software, emphasizing the need for regular security assessments and vulnerability management programs that can identify and remediate similar issues across the entire network infrastructure stack.