CVE-2015-6429 in IOS
Summary
by MITRE
The IKEv1 state machine in Cisco IOS 15.4 through 15.6 and IOS XE 3.15 through 3.17 allows remote attackers to cause a denial of service (IPsec connection termination) via a crafted IKEv1 packet to a tunnel endpoint, aka Bug ID CSCuw08236.
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Analysis
by VulDB Data Team • 07/01/2022
The vulnerability described in CVE-2015-6429 represents a critical flaw in the Internet Key Exchange version 1 implementation within Cisco IOS and IOS XE operating systems. This issue affects versions ranging from IOS 15.4 through 15.6 and IOS XE 3.15 through 3.17, making it a widespread concern across multiple Cisco networking platforms that rely on IPsec tunneling for secure communications. The vulnerability specifically targets the IKEv1 state machine, which is responsible for establishing and maintaining secure connections between network devices using IPsec protocols.
The technical flaw manifests when a remote attacker crafts specially formatted IKEv1 packets and sends them to a vulnerable tunnel endpoint. These crafted packets exploit a weakness in how the IKEv1 state machine processes incoming messages, causing the system to enter an inconsistent state that ultimately results in the termination of active IPsec connections. This behavior is classified as a denial of service condition because legitimate users and systems relying on these secure tunnels will experience abrupt disconnections and loss of secure network connectivity. The vulnerability does not allow for arbitrary code execution or unauthorized access to system resources, but rather focuses on disrupting the availability of secure communication channels.
The operational impact of this vulnerability extends beyond simple service disruption, as IPsec tunnels are fundamental to secure network communications in enterprise and service provider environments. When these tunnels terminate unexpectedly, it can lead to complete loss of connectivity between remote sites, branch offices, or secure network segments. Network administrators may experience cascading failures as dependent services and applications lose their secure communication paths, potentially affecting business continuity and network reliability. The vulnerability is particularly concerning because it can be exploited remotely without requiring authentication, making it accessible to any attacker who can reach the affected network devices.
Cisco has addressed this vulnerability through software updates and patches that modify the IKEv1 state machine implementation to properly validate and handle crafted packets. Organizations should implement these updates immediately to protect their networks from exploitation. Additional mitigations include implementing network segmentation to limit exposure, monitoring for unusual IKE traffic patterns, and configuring access controls to restrict which external sources can communicate with tunnel endpoints. From a cybersecurity perspective, this vulnerability aligns with CWE-121, which addresses buffer overflow conditions, and maps to ATT&CK technique T1499.002 for network denial of service attacks. The vulnerability demonstrates the importance of proper state machine validation in network protocol implementations and highlights the critical need for robust input validation in security-sensitive components of network infrastructure software.