CVE-2011-4326 in Linux
Summary
by MITRE
The udp6_ufo_fragment function in net/ipv6/udp.c in the Linux kernel before 2.6.39, when a certain UDP Fragmentation Offload (UFO) configuration is enabled, allows remote attackers to cause a denial of service (system crash) by sending fragmented IPv6 UDP packets to a bridge device.
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Analysis
by VulDB Data Team • 12/01/2021
The vulnerability identified as CVE-2011-4326 represents a critical denial of service flaw within the Linux kernel's IPv6 UDP implementation. This vulnerability specifically affects systems running Linux kernel versions prior to 2.6.39 and manifests when UDP Fragmentation Offload (UFO) is enabled on bridge devices. The flaw resides in the udp6_ufo_fragment function located in the net/ipv6/udp.c source file, which handles the fragmentation of IPv6 UDP packets when UFO is active. The vulnerability demonstrates how improper handling of fragmented packets can lead to system instability and complete crash conditions, making it a significant concern for network infrastructure components that rely on IPv6 communication and bridge functionality.
The technical root cause of this vulnerability stems from inadequate validation and processing of fragmented IPv6 UDP packets within the kernel's network stack when UFO is enabled. When a bridge device receives fragmented IPv6 UDP packets while UFO is configured, the udp6_ufo_fragment function fails to properly handle the fragmentation process, leading to memory corruption or invalid pointer dereferences. This occurs because the function does not adequately verify the integrity of fragmented packet structures or properly manage the memory allocation and deallocation processes associated with fragmented data. The flaw specifically exploits the interaction between the UFO feature, which is designed to offload packet fragmentation to network hardware, and the bridge device's packet processing pipeline, creating a scenario where malformed or specially crafted fragmented packets can trigger kernel panic conditions.
The operational impact of this vulnerability extends beyond simple service disruption to encompass complete system compromise and potential denial of service across entire network infrastructures. Attackers can exploit this vulnerability by sending carefully crafted fragmented IPv6 UDP packets to bridge devices, causing the target system to crash and reboot automatically. This type of attack is particularly dangerous in network environments where bridge devices serve as critical infrastructure components, as it can lead to widespread service outages and network partitioning. The vulnerability affects systems where IPv6 communication is enabled and bridge functionality is active, making it relevant to enterprise networks, data centers, and any infrastructure relying on IPv6 with bridge configurations. The impact is amplified because the vulnerability can be exploited remotely without requiring authentication or special privileges, making it a preferred target for network-level denial of service attacks.
Mitigation strategies for CVE-2011-4326 primarily focus on kernel updates and configuration modifications to prevent exploitation. The most effective solution involves upgrading to Linux kernel version 2.6.39 or later, where the vulnerability has been addressed through proper validation of fragmented packet structures and enhanced memory management during UFO processing. System administrators should also consider disabling UDP Fragmentation Offload on bridge devices when this functionality is not strictly required, as this removes the vulnerable code path entirely. Network segmentation and access control measures can provide additional protection by limiting exposure to potentially malicious traffic. The vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and represents a classic example of improper input validation leading to system instability. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, which covers network denial of service attacks, and demonstrates how kernel-level flaws can be exploited to achieve system-level compromise. Organizations should implement regular patch management processes and conduct vulnerability assessments to ensure all network infrastructure components remain protected against similar vulnerabilities that could affect system stability and availability.