CVE-2011-2393 in FreeBSD
Summary
by MITRE
The Neighbor Discovery (ND) protocol implementation in the IPv6 stack in FreeBSD, NetBSD, and possibly other BSD-based operating systems allows remote attackers to cause a denial of service (CPU consumption and device hang) by sending many Router Advertisement (RA) messages with different source addresses, a similar vulnerability to CVE-2010-4670.
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Analysis
by VulDB Data Team • 01/18/2018
The vulnerability identified as CVE-2011-2393 represents a significant denial of service weakness within the IPv6 stack implementations of several BSD-based operating systems including FreeBSD and NetBSD. This flaw specifically targets the Neighbor Discovery protocol which is a fundamental component of IPv6 network operations responsible for address resolution, router discovery, and neighbor unreachability detection. The vulnerability manifests when the system receives an excessive number of Router Advertisement messages with varying source addresses, creating a condition that can lead to complete system resource exhaustion and operational paralysis.
The technical mechanism underlying this vulnerability resides in the insufficient validation and handling of incoming Router Advertisement messages within the IPv6 stack implementation. When multiple RA messages are received with different source addresses, the system's neighbor discovery protocol processing becomes overwhelmed as it attempts to maintain and update its neighbor cache entries for each unique source address. This processing consumes substantial CPU cycles and memory resources, with the system's handling of these messages becoming increasingly inefficient as the number of distinct source addresses grows. The flaw operates at the network protocol level and can be exploited by remote attackers without requiring authentication or privileged access, making it particularly dangerous in networked environments where IPv6 traffic is present.
The operational impact of this vulnerability extends beyond simple service disruption to potentially causing complete system hang conditions that can affect network availability and system stability. Attackers can exploit this weakness by crafting and transmitting a large volume of Router Advertisement messages with spoofed source addresses, effectively consuming system resources at a rate that can overwhelm the device's processing capabilities. The vulnerability creates a resource exhaustion scenario where the system's CPU utilization spikes to maximum levels while memory consumption increases dramatically, often resulting in the device becoming unresponsive to legitimate network traffic and potentially requiring manual intervention or reboot to restore normal operations. This type of denial of service attack can be particularly damaging in network infrastructure devices such as routers, firewalls, and servers that rely heavily on IPv6 functionality.
Mitigation strategies for CVE-2011-2393 should focus on implementing network-level controls and system configuration adjustments to limit the impact of malicious Router Advertisement traffic. Network administrators should consider implementing rate limiting mechanisms at the network perimeter to restrict the number of Router Advertisement messages that can be processed within a given time frame. System administrators should also consider disabling unnecessary IPv6 neighbor discovery features or implementing strict filtering rules that validate source addresses against known legitimate ranges. The vulnerability aligns with CWE-400 which classifies it as a resource exhaustion weakness, and it maps to ATT&CK technique T1499.001 which describes network denial of service attacks. Organizations should prioritize applying vendor-specific patches and updates as they become available, while also implementing monitoring solutions that can detect unusual patterns of Router Advertisement traffic to identify potential exploitation attempts. Additionally, implementing proper network segmentation and access control measures can help limit the scope of impact if an attack does occur, preventing lateral movement and reducing the overall attack surface.