CVE-2005-2451 in IOS
Summary
by MITRE
Cisco IOS 12.0 through 12.4 and IOS XR before 3.2, with IPv6 enabled, allows remote attackers on a local network segment to cause a denial of service (device reload) and possibly execute arbitrary code via a crafted IPv6 packet.
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Analysis
by VulDB Data Team • 06/30/2025
This vulnerability exists in Cisco IOS versions 12.0 through 12.4 and IOS XR versions before 3.2 when IPv6 functionality is enabled on network devices. The flaw represents a critical security issue that can be exploited by attackers positioned on the same local network segment to remotely trigger device instability and potentially gain unauthorized code execution privileges. The vulnerability specifically manifests when the affected Cisco IOS implementations process malformed or crafted IPv6 packets that contain specially constructed headers or options fields. This issue falls under the CWE-121 category of buffer copy without merging bounds checking, indicating that the system fails to properly validate the boundaries of IPv6 packet data structures during processing. The attack vector requires an attacker to be on the same local network segment as the vulnerable device, which aligns with the ATT&CK technique T1046 for network service scanning and T1498 for network denial of service attacks. When exploited, the vulnerability causes the targeted Cisco device to crash and reload, resulting in a denial of service condition that disrupts network connectivity and services. The potential for arbitrary code execution adds an additional layer of severity, as successful exploitation could allow attackers to gain persistent access to the network infrastructure. The root cause stems from insufficient input validation within the IPv6 processing modules of the IOS kernel, where the system does not properly sanitize or validate IPv6 packet contents before attempting to parse and process them. This lack of proper bounds checking allows malicious packet structures to overwrite critical memory locations or trigger unexpected behavior in the device's network stack implementation.
The operational impact of this vulnerability extends beyond simple service disruption to encompass potential network infrastructure compromise and extended downtime for affected organizations. Network administrators managing Cisco devices in environments where IPv6 is enabled face significant risk, particularly in enterprise networks where multiple devices may be vulnerable across different operational segments. The vulnerability affects a wide range of Cisco network equipment including routers and switches that support the affected IOS versions. Organizations with distributed networks or those utilizing IPv6 for network expansion are especially at risk, as the attack requires only local network access to exploit the flaw. The potential for remote code execution means that successful exploitation could enable attackers to establish persistent backdoors, modify routing tables, or redirect network traffic to malicious destinations. Security teams must consider the implications for network availability, as the device reload condition can occur without any user interaction, potentially leading to cascading failures in network infrastructure. The vulnerability's impact is amplified in environments where network devices serve as critical infrastructure components, such as core routers or border gateways where service disruption can affect large portions of network connectivity.
Mitigation strategies for this vulnerability should focus on immediate patching of affected Cisco IOS versions to address the underlying buffer overflow conditions in IPv6 processing. Cisco released security advisories and patches specifically addressing this vulnerability in their IOS software releases, and organizations should prioritize applying these updates to all affected devices. Network segmentation and access control measures can help reduce the attack surface by limiting local network access to only authorized personnel and systems. Implementing IPv6 traffic filtering rules and disabling IPv6 functionality on devices where it is not required provides an additional defense in depth approach. Network monitoring solutions should be configured to detect anomalous IPv6 packet patterns that may indicate exploitation attempts. Regular vulnerability assessments and penetration testing can help identify other potential vulnerabilities in the network infrastructure that may be exploited in conjunction with this flaw. Organizations should also implement proper incident response procedures to quickly identify and contain exploitation attempts, including network isolation of affected devices and forensic analysis of attack patterns. The implementation of network access control lists and firewall rules that filter IPv6 traffic at network boundaries can provide additional protection against exploitation attempts from external sources. Security teams should maintain updated inventories of all network devices running affected IOS versions to ensure comprehensive coverage of patching efforts. The vulnerability serves as a reminder of the importance of proper input validation and bounds checking in network protocol implementations, aligning with security best practices outlined in frameworks such as NIST SP 800-53 and ISO 27001 standards for secure network design and implementation.