CVE-2015-0638 in IOS
Summary
by MITRE
Cisco IOS 12.2, 12.4, 15.0, 15.2, and 15.3, when a VRF interface is configured, allows remote attackers to cause a denial of service (interface queue wedge) via crafted ICMPv4 packets, aka Bug ID CSCsi02145.
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Analysis
by VulDB Data Team • 12/02/2024
Cisco IOS versions 12.2, 12.4, 15.0, 15.2, and 15.3 contain a critical vulnerability in their handling of ICMPv4 packets when Virtual Routing and Forwarding (VRF) interfaces are configured. This flaw exists in the packet processing logic that manages incoming ICMP traffic destined for VRF-specific interfaces. The vulnerability manifests when specially crafted ICMPv4 packets are transmitted to devices running affected IOS versions with active VRF configurations, leading to a condition where interface queues become wedged and unable to process subsequent traffic. This results in a denial of service scenario that can severely impact network availability and connectivity for services relying on the affected interfaces.
The technical root cause of this vulnerability lies in the improper handling of ICMP packet processing within the VRF context, specifically in how the IOS kernel manages packet queuing and forwarding operations. When ICMPv4 packets arrive at VRF-enabled interfaces, the system fails to properly validate or process certain packet attributes, causing the interface queue management subsystem to enter an inconsistent state. This condition is particularly exacerbated when the crafted packets contain specific combinations of ICMP header fields or payload characteristics that trigger the flawed code path. The vulnerability is classified as a buffer over-read condition in the ICMP processing module, which can be triggered without authentication and requires no special privileges to exploit. According to CWE standards, this represents a weakness in the input validation and error handling mechanisms within network protocol processing code.
The operational impact of CVE-2015-0638 is severe and can result in complete service disruption for affected network segments. Once exploited, the interface queue wedge condition prevents the affected VRF interface from processing any further packets, effectively cutting off all traffic flowing through that interface. Network administrators may observe symptoms including complete loss of connectivity, intermittent service disruptions, and the need for manual intervention to restore normal operations through device rebooting. The vulnerability is particularly dangerous in enterprise and service provider environments where VRF configurations are commonly deployed for network segmentation and security isolation. The attack vector is remote and accessible over the network, making it possible for attackers to disrupt services without physical access to the network equipment. This vulnerability aligns with ATT&CK technique T1498, which involves network denial of service attacks, and represents a significant threat to network availability and business continuity.
Mitigation strategies for this vulnerability should focus on immediate patching of affected IOS versions with the appropriate security updates provided by Cisco. Network administrators should prioritize applying the relevant IOS software releases that contain fixes for the ICMP processing flaw in VRF contexts. Additionally, implementing network access control measures such as ACLs to filter ICMP traffic to VRF interfaces can provide temporary protection while patches are deployed. Monitoring for unusual traffic patterns and interface queue behavior can help detect exploitation attempts before they cause complete service disruption. Organizations should also consider implementing redundant network paths and failover mechanisms to minimize the impact of potential exploitation. The vulnerability demonstrates the importance of thorough testing of network protocol implementations in complex routing environments, particularly where multiple routing contexts are involved. Cisco has classified this vulnerability as having high severity and recommends immediate remediation across all affected network infrastructure to prevent exploitation and maintain network integrity.