CVE-2011-4087 in Linux
Summary
by MITRE
The br_parse_ip_options function in net/bridge/br_netfilter.c in the Linux kernel before 2.6.39 does not properly initialize a certain data structure, which allows remote attackers to cause a denial of service by leveraging connectivity to a network interface that uses an Ethernet bridge device.
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Analysis
by VulDB Data Team • 01/03/2022
The vulnerability described in CVE-2011-4087 resides within the Linux kernel's bridge netfilter implementation, specifically in the br_parse_ip_options function located in net/bridge/br_netfilter.c. This flaw affects Linux kernel versions prior to 2.6.39 and represents a classic case of improper data structure initialization that can be exploited to trigger system instability. The vulnerability occurs within the network bridge subsystem where packets are processed and filtered, creating a potential attack surface that remote adversaries can leverage through network connectivity to affected interfaces.
The technical root cause of this vulnerability stems from the failure to properly initialize a critical data structure within the br_parse_ip_options function. When network packets traverse through an Ethernet bridge device, the kernel's netfilter framework processes IP options contained within these packets. The incomplete initialization of the data structure means that certain memory regions may contain unpredictable values or stale data, which can lead to undefined behavior during packet processing. This improper initialization creates a condition where the kernel's bridge netfilter module cannot correctly handle specific packet formats, particularly those containing crafted IP options that trigger the vulnerable code path.
The operational impact of this vulnerability manifests as a remote denial of service condition that can be triggered without authentication or privileged access. An attacker positioned on the network can send specially crafted packets through a network interface that utilizes an Ethernet bridge device, causing the kernel to crash or become unresponsive. This affects systems running Linux kernels before version 2.6.39 that have bridge networking capabilities enabled, potentially disrupting network connectivity for all bridge-enabled interfaces on the affected system. The vulnerability is particularly concerning because it can be exploited from remote locations and does not require specialized privileges or access to the target system.
From a cybersecurity perspective, this vulnerability aligns with CWE-457: Use of Uninitialized Variable, which represents a fundamental programming error that can lead to unpredictable behavior and system instability. The attack pattern follows the ATT&CK technique T1499.004: Endpoint Denial of Service, where adversaries target system resources to prevent legitimate use of services. The vulnerability demonstrates how seemingly minor initialization errors in kernel code can have significant operational consequences, particularly in network infrastructure components where reliability is paramount. Organizations using Linux systems with bridge networking capabilities should prioritize patching to address this vulnerability, as it represents a straightforward yet impactful denial of service risk that can affect network availability and system stability.
The remediation approach for this vulnerability requires updating the Linux kernel to version 2.6.39 or later, where the improper data structure initialization has been corrected. System administrators should conduct thorough testing of kernel updates in controlled environments before deployment to ensure compatibility with existing network configurations and applications. Additionally, network segmentation strategies and firewall rules can be implemented to limit exposure where immediate patching is not feasible, though this represents a temporary mitigation rather than a permanent solution. Regular security assessments and vulnerability scanning should include verification of kernel versions to prevent exploitation of similar initialization flaws in other kernel subsystems.