CVE-2015-0695 in IOS XR
Summary
by MITRE
Cisco IOS XR 4.3.4 through 5.3.0 on ASR 9000 devices, when uRPF, PBR, QoS, or an ACL is configured, does not properly handle bridge-group virtual interface (BVI) traffic, which allows remote attackers to cause a denial of service (chip and card hangs and reloads) by triggering use of a BVI interface for IPv4 packets, aka Bug ID CSCur62957.
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Analysis
by VulDB Data Team • 05/09/2022
The vulnerability described in CVE-2015-0695 represents a critical denial of service flaw affecting Cisco IOS XR software versions 4.3.4 through 5.3.0 on ASR 9000 series devices. This issue specifically manifests when certain network configuration elements such as uRPF, PBR, QoS, or ACLs are implemented alongside bridge-group virtual interface (BVI) configurations. The flaw operates at the fundamental level of packet processing within the router's forwarding plane, creating a condition where legitimate network traffic can trigger system-wide failures. The vulnerability falls under the category of improper handling of network interface configurations and is classified as a software defect in the routing and switching functionality of the affected Cisco platforms.
The technical mechanism behind this vulnerability involves the improper processing of IPv4 packets when they traverse BVI interfaces in conjunction with the aforementioned network policies. When a BVI interface is configured and utilized for IPv4 packet forwarding, the system fails to correctly manage the traffic flow through the hardware forwarding engine. This mismanagement leads to a condition where the chip and card components responsible for packet processing become overwhelmed or enter an inconsistent state. The flaw specifically occurs during the packet processing phase when the system attempts to handle the interaction between BVI interface operations and the configured policies, resulting in a cascade of failures that ultimately require system reloads to resolve. The vulnerability is particularly dangerous because it can be triggered remotely without requiring authentication, making it exploitable by attackers who can craft specific packet flows to trigger the condition.
The operational impact of this vulnerability extends beyond simple service interruption to potentially compromise the entire network infrastructure managed by affected ASR 9000 devices. When triggered, the vulnerability causes complete system hangs and forced reloads that can result in significant network downtime and potential loss of connectivity for services relying on these core routing devices. The affected devices may experience complete chip failures or card-level malfunctions, requiring manual intervention to restore normal operation. This type of vulnerability directly impacts network availability and reliability, particularly in carrier and enterprise environments where ASR 9000 devices serve as critical backbone routers. The vulnerability's potential for remote exploitation means that network administrators cannot rely on simple access controls to prevent exploitation, as the attack can be initiated from outside the network perimeter.
Mitigation strategies for this vulnerability require immediate implementation of software updates and configuration changes to prevent the triggering conditions. Cisco has released patches and software updates specifically addressing this issue, which should be deployed across all affected devices as a priority. Network administrators should also implement configuration changes to avoid the specific combination of uRPF, PBR, QoS, ACL, and BVI interface usage that triggers the vulnerability. The remediation process involves either upgrading to patched software versions or carefully reconfiguring network policies to avoid the problematic interface combinations. Organizations should also implement monitoring solutions to detect potential exploitation attempts and establish incident response procedures for rapid recovery from any successful attacks. This vulnerability demonstrates the importance of thorough testing of network configuration combinations and highlights the need for robust vulnerability management processes in critical network infrastructure.
The vulnerability aligns with CWE-119 which addresses improper handling of memory access violations and represents a classic example of how complex network configurations can create unexpected interaction points that lead to system instability. From an ATT&CK perspective, this vulnerability maps to the T1499.004 technique for network denial of service and the T1059.007 technique for command and scripting interpreter through remote access. The attack surface is particularly concerning for network security teams as it demonstrates how seemingly routine network configuration elements can combine to create critical system failures. This vulnerability also underscores the importance of network segmentation and the need for comprehensive network testing procedures to identify interaction points that could lead to denial of service conditions in production environments.