CVE-2015-4203 in IOS
Summary
by MITRE
Race condition in Cisco IOS 12.2SCH in the Performance Routing Engine (PRE) module on uBR10000 devices, when NetFlow and an MPLS IPv6 VPN are configured, allows remote attackers to cause a denial of service (PXF process crash) by sending malformed MPLS 6VPE packets quickly, aka Bug ID CSCud83396.
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Analysis
by VulDB Data Team • 05/21/2022
The vulnerability identified as CVE-2015-4203 represents a critical race condition within the Performance Routing Engine module of Cisco IOS software version 12.2SCH, specifically affecting uBR10000 series devices. This flaw exists in the interaction between the Performance Routing Engine and the NetFlow monitoring functionality when configured alongside MPLS IPv6 VPN services, creating a pathway for remote attackers to exploit the system's processing mechanisms. The vulnerability manifests as a denial of service condition that results in the complete crash of the PXF (Performance eXtension Framework) process, effectively rendering the affected routing device non-functional and disrupting network connectivity for all services dependent on that device.
The technical root cause of this vulnerability stems from improper synchronization mechanisms within the PRE module's handling of MPLS 6VPE packet processing. When malformed MPLS 6VPE packets are transmitted rapidly to the affected device, the race condition allows for concurrent access to shared memory resources and processing states without proper mutual exclusion controls. This condition is particularly dangerous because it occurs during the normal packet processing flow when NetFlow and MPLS IPv6 VPN configurations are active, making the vulnerability exploitable through standard network traffic without requiring privileged access or authentication. The flaw specifically affects the PXF process which is responsible for performance monitoring and routing optimization functions, causing it to terminate unexpectedly and requiring manual intervention to restore service.
The operational impact of this vulnerability extends beyond simple service disruption, as it can affect large-scale network infrastructures where uBR10000 devices serve as core routing points for MPLS networks. Network administrators face the potential for cascading failures when these devices crash, particularly in environments where multiple services depend on the same routing infrastructure. The vulnerability is especially concerning in enterprise and service provider networks where high availability is critical, as the PXF process crash can result in complete routing table corruption and loss of connectivity for all MPLS 6VPE services. The rapid transmission of malformed packets required to exploit this vulnerability means that attacks can be executed with minimal resources, making the threat particularly dangerous in environments where network monitoring systems may not immediately detect the attack patterns.
Mitigation strategies for CVE-2015-4203 focus on both immediate protective measures and long-term architectural improvements. Network administrators should prioritize applying the relevant Cisco security patches and updates that address the race condition in the PRE module, while also implementing packet filtering rules to limit the types of MPLS 6VPE packets that can reach the vulnerable devices. The implementation of rate limiting and ingress filtering can help prevent the rapid transmission patterns necessary to trigger the vulnerability. Additionally, network segmentation and redundancy planning should be enhanced to ensure that the failure of individual devices does not result in complete service outages. From a compliance perspective, this vulnerability aligns with CWE-362 which addresses race conditions in concurrent systems, and it maps to ATT&CK technique T1499.004 for network disruption attacks. Organizations should also consider implementing continuous monitoring solutions that can detect anomalous packet patterns and process crashes, enabling faster incident response and reducing the window of opportunity for exploitation. The vulnerability underscores the importance of proper synchronization mechanisms in network device firmware and highlights the need for comprehensive security testing of concurrent processing components in enterprise networking equipment.