CVE-2013-5474 in IOS
Summary
by MITRE
Race condition in the IPv6 virtual fragmentation reassembly (VFR) implementation in Cisco IOS 12.2 through 12.4 and 15.0 through 15.3 allows remote attackers to cause a denial of service (device reload or hang) via fragmented IPv6 packets, aka Bug ID CSCud64812.
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Analysis
by VulDB Data Team • 12/24/2024
The vulnerability identified as CVE-2013-5474 represents a critical race condition within the IPv6 virtual fragmentation reassembly functionality of Cisco IOS software versions ranging from 12.2 through 12.4 and 15.0 through 15.3. This flaw specifically affects the handling of fragmented IPv6 packets and operates at the network layer where IPv6 packets are processed and reassembled. The vulnerability manifests when the device encounters fragmented IPv6 packets that trigger the virtual fragmentation reassembly mechanism, which is designed to handle large packets that exceed the maximum transmission unit of network segments. The race condition occurs during the reassembly process when multiple threads or processes attempt to access and modify shared memory structures simultaneously without proper synchronization mechanisms, creating a timing window where the system can enter an inconsistent state.
The technical implementation of this vulnerability stems from improper handling of concurrent packet processing within the IPv6 reassembly code path. When an attacker sends carefully crafted fragmented IPv6 packets to a vulnerable Cisco IOS device, the system's VFR implementation attempts to reassemble these fragments into complete packets. However, due to the race condition, the reassembly process can encounter situations where fragment data is being written to memory locations while other processes are simultaneously reading from or modifying the same locations. This creates a scenario where the device's memory management structures become corrupted or the reassembly state machine enters an invalid state. The flaw is particularly dangerous because it operates at the kernel level of the IOS operating system, where the device's core networking functions reside, making it capable of triggering system-wide instability.
The operational impact of this vulnerability extends beyond simple service disruption, as it can cause complete device reloads or system hangs that effectively deny network services to legitimate users. When the race condition is successfully exploited, the vulnerable device may experience a kernel panic or a state where it becomes unresponsive to network traffic, requiring manual intervention or automatic restart to restore functionality. Network administrators may observe intermittent connectivity issues, sudden device reboots, or complete network outages depending on the attack pattern and the device's configuration. The vulnerability affects a wide range of Cisco networking equipment including routers, switches, and other network infrastructure devices running the affected IOS versions, making it particularly concerning for enterprise and service provider networks where such devices form the backbone of network connectivity.
Cisco's official bug ID CSCud64812 documents this vulnerability as part of the broader category of race conditions in network protocol implementations, which fall under CWE-362 - Concurrent Execution using Shared Resource with Unprotected Race Condition. The attack vector requires remote access to the network, making it particularly dangerous as it can be exploited from outside the network perimeter without requiring physical access or authentication credentials. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1499.002 - Endpoint Denial of Service, specifically targeting network infrastructure devices to cause service disruption. The exploitation process typically involves sending a sequence of fragmented IPv6 packets designed to trigger the specific timing conditions necessary to exploit the race condition, potentially requiring minimal computational resources from the attacker while causing maximum disruption to network services.
Mitigation strategies for this vulnerability include immediate deployment of Cisco's security patches and software updates that address the race condition in the IPv6 VFR implementation. Network administrators should prioritize updating all affected Cisco IOS devices to versions that contain the necessary fixes, which typically involve proper synchronization mechanisms and improved memory management during packet reassembly operations. Additional defensive measures include implementing IPv6 access control lists to filter suspicious fragmented traffic, disabling IPv6 virtual fragmentation reassembly on devices where it is not strictly required, and monitoring network traffic for unusual patterns of fragmented IPv6 packets that may indicate exploitation attempts. Organizations should also consider implementing network segmentation strategies to limit the potential impact of such attacks and maintain comprehensive network monitoring to detect anomalous behavior that could indicate exploitation of this vulnerability.