CVE-2011-0709 in Linux
Summary
by MITRE
The br_mdb_ip_get function in net/bridge/br_multicast.c in the Linux kernel before 2.6.35-rc5 allows remote attackers to cause a denial of service (NULL pointer dereference and system crash) via an IGMP packet, related to lack of a multicast table.
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Analysis
by VulDB Data Team • 10/17/2021
The vulnerability described in CVE-2011-0709 represents a critical denial of service flaw within the Linux kernel's bridge multicast handling mechanism. This issue specifically affects the br_mdb_ip_get function located in the net/bridge/br_multicast.c source file, which is responsible for managing multicast group memberships in bridge networking components. The vulnerability emerged in kernel versions prior to 2.6.35-rc5 and demonstrates a fundamental flaw in input validation and state management within the multicast subsystem. The flaw occurs when the kernel processes IGMP (Internet Group Management Protocol) packets without proper validation of multicast table entries, creating a scenario where a remote attacker can trigger system instability through carefully crafted network traffic.
The technical implementation of this vulnerability stems from a NULL pointer dereference condition that occurs when the br_mdb_ip_get function attempts to access multicast table entries that have not been properly initialized or have been removed from the system. This function is part of the bridge multicast database management system that tracks which network interfaces are interested in specific multicast groups. When an IGMP packet arrives that references a multicast entry that does not exist in the kernel's internal multicast table structure, the function fails to properly validate the existence of the entry before attempting to dereference it. This failure results in a NULL pointer dereference that causes the kernel to crash and reboot the affected system. The vulnerability is classified under CWE-476 as a NULL pointer dereference, which represents a common class of software defects that can lead to system instability and denial of service conditions.
From an operational perspective, this vulnerability presents a significant risk to network infrastructure systems that rely on Linux bridge functionality, particularly in environments where multicast traffic is prevalent such as video streaming services, network monitoring systems, and enterprise network switches. The remote nature of the attack means that any system running an affected kernel version and processing IGMP packets is potentially vulnerable to exploitation without requiring local access or authentication. Network administrators managing bridge-based networking equipment, including routers, switches, and firewalls that utilize Linux kernel networking stacks, face substantial operational risk from this vulnerability. The impact extends beyond simple service disruption to potentially compromising network availability for extended periods, as system crashes require manual intervention and reboot cycles that can disrupt network services for minutes or hours depending on the recovery process.
The exploitation of this vulnerability aligns with ATT&CK technique T1499.004 for network denial of service attacks, where adversaries leverage system weaknesses to disrupt availability of network services. Organizations implementing bridge networking solutions, including those using Linux-based network appliances, software-defined networking (SDN) controllers, and network virtualization platforms, must prioritize patching this vulnerability. The recommended mitigation strategy involves upgrading to Linux kernel version 2.6.35-rc5 or later, where the multicast table validation has been properly implemented to prevent NULL pointer dereference conditions. Additionally, network administrators should consider implementing network segmentation and access controls to limit exposure to potentially malicious IGMP traffic, though the most effective defense remains the timely application of kernel patches. Security monitoring should include detection of unusual IGMP packet patterns that might indicate attempted exploitation of this vulnerability, particularly in environments where multicast traffic is not regularly expected or properly managed.