CVE-2010-3696 in FreeRADIUS
Summary
by MITRE
The fr_dhcp_decode function in lib/dhcp.c in FreeRADIUS 2.1.9, in certain non-default builds, does not properly handle the DHCP Relay Agent Information option, which allows remote attackers to cause a denial of service (infinite loop and daemon outage) via a packet that has more than one sub-option. NOTE: some of these details are obtained from third party information.
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Analysis
by VulDB Data Team • 09/26/2021
The vulnerability identified as CVE-2010-3696 resides within the FreeRADIUS 2.1.9 software suite, specifically in the fr_dhcp_decode function located in lib/dhcp.c. This flaw represents a critical security issue that affects certain non-default build configurations of the widely-used RADIUS server implementation. The vulnerability manifests when the DHCP Relay Agent Information option is improperly handled during packet processing, creating a condition that can be exploited by remote attackers to disrupt service availability.
The technical implementation of this vulnerability stems from inadequate input validation within the DHCP decoding routine. When processing DHCP packets containing the Relay Agent Information option, the fr_dhcp_decode function fails to properly manage scenarios where multiple sub-options are present within a single option field. This improper handling creates a logic flaw that results in an infinite loop during packet processing, causing the FreeRADIUS daemon to become unresponsive and effectively rendering the authentication service unavailable to legitimate users. The flaw operates at the protocol parsing layer, making it particularly dangerous as it can be triggered by malformed network traffic without requiring authentication or elevated privileges.
From an operational impact perspective, this vulnerability presents a severe denial of service threat to organizations relying on FreeRADIUS for network authentication services. The infinite loop condition causes the daemon to consume excessive CPU resources while remaining unresponsive to legitimate authentication requests, leading to complete service disruption. Network administrators may experience extended outages as the daemon must be manually restarted to restore functionality, potentially affecting thousands of concurrent users depending on the network infrastructure. This vulnerability particularly impacts environments where DHCP relay functionality is enabled, as these configurations are more likely to encounter the problematic packet structures that trigger the flaw.
The vulnerability aligns with CWE-835, which addresses the issue of infinite loops in software implementations, and represents a classic example of a resource exhaustion attack that can be executed remotely. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, which covers network denial of service attacks, and T1595.001, which involves network scanning and reconnaissance activities that can identify vulnerable systems. Organizations should implement immediate mitigations including applying the vendor-provided patches, configuring network segmentation to limit exposure, and implementing monitoring solutions to detect anomalous daemon behavior. Additionally, system administrators should consider disabling unnecessary DHCP relay functionality when not required, and maintain regular vulnerability assessments to identify similar implementation flaws in other network services. The incident underscores the importance of thorough input validation in protocol parsing implementations and highlights the critical need for comprehensive testing of edge cases in network infrastructure software to prevent such service disruption vulnerabilities.