CVE-2011-2942 in Linux
Summary
by MITRE
A certain Red Hat patch to the __br_deliver function in net/bridge/br_forward.c in the Linux kernel 2.6.18 on Red Hat Enterprise Linux (RHEL) 5 allows remote attackers to cause a denial of service (NULL pointer dereference and system crash) or possibly have unspecified other impact by leveraging connectivity to a network interface that uses an Ethernet bridge device.
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Analysis
by VulDB Data Team • 03/20/2021
The vulnerability described in CVE-2011-2942 represents a critical NULL pointer dereference flaw within the Linux kernel's bridge forwarding mechanism. This issue specifically affects the __br_deliver function located in net/bridge/br_forward.c of the 2.6.18 kernel version distributed with Red Hat Enterprise Linux 5. The vulnerability arises from insufficient input validation and error handling within the bridge forwarding code path, creating a condition where malicious network traffic can trigger a system crash through a NULL pointer dereference. The flaw is particularly concerning because it can be exploited remotely by attackers who have network connectivity to interfaces utilizing Ethernet bridge devices, making it accessible to a wide range of potential threat actors.
The technical implementation of this vulnerability stems from the improper handling of packet delivery within the kernel's bridge forwarding subsystem. When the __br_deliver function processes network packets through bridged interfaces, it fails to properly validate pointer references before dereferencing them. This condition allows an attacker to construct specially crafted network packets that, when processed by the bridge forwarding code, cause the kernel to attempt to access a NULL memory address. The resulting NULL pointer dereference immediately terminates the kernel execution context and causes a system crash, effectively creating a denial of service condition that can be triggered remotely without requiring authentication or special privileges. The vulnerability is classified under CWE-476 as a NULL Pointer Dereference, which represents a common but dangerous class of software defects in kernel space programming.
The operational impact of CVE-2011-2942 extends beyond simple service disruption to potentially compromise system availability and stability in production environments. Systems running affected kernel versions that utilize Ethernet bridging capabilities become vulnerable to remote exploitation, which can result in complete system outages. This vulnerability affects network infrastructure components such as routers, switches, and network appliances that rely on Linux kernel bridging functionality, making it particularly dangerous in enterprise and data center environments where network availability is critical. The remote exploitability means that attackers can trigger the vulnerability from outside the local network perimeter, amplifying the potential impact and reducing the attack surface requirements. The unspecified other impacts mentioned in the original description suggest that this vulnerability may potentially be leveraged for more advanced exploitation techniques beyond simple DoS, though the primary concern remains system crash and availability disruption.
Mitigation strategies for CVE-2011-2942 primarily focus on applying the vendor-provided security patches and updates that address the NULL pointer dereference in the kernel's bridge forwarding code. Red Hat released specific patches for RHEL 5 that correct the validation logic within the __br_deliver function, ensuring that pointer references are properly checked before dereferencing. System administrators should immediately apply these patches to all affected systems, particularly those operating in production environments where network bridging is utilized. Alternative mitigations include disabling Ethernet bridging functionality on affected systems, implementing network segmentation to isolate vulnerable components, and deploying intrusion detection systems to monitor for exploitation attempts. Organizations should also consider implementing network access controls and firewall rules to limit connectivity to bridged interfaces, reducing the attack surface for potential exploitation. The vulnerability demonstrates the importance of kernel security auditing and the critical need for proper input validation in kernel space code, as highlighted by ATT&CK technique T1499.004 for Network Denial of Service and T1562.001 for Impairing Defenses, which both relate to the operational impact of such vulnerabilities in network infrastructure systems.