CVE-2005-3669 in IOS
Summary
by MITRE
Multiple unspecified vulnerabilities in the Internet Key Exchange version 1 (IKEv1) implementation in multiple Cisco products allow remote attackers to cause a denial of service (device reset) via certain malformed IKE packets, as demonstrated by the PROTOS ISAKMP Test Suite for IKEv1. NOTE: due to the lack of details in the Cisco advisory, it is unclear which of CVE-2005-3666, CVE-2005-3667, and/or CVE-2005-3668 this issue applies to.
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Analysis
by VulDB Data Team • 06/29/2025
The vulnerability identified as CVE-2005-3669 represents a critical weakness in the Internet Key Exchange version 1 protocol implementation within Cisco network devices. This issue affects multiple Cisco products that utilize IKEv1 for establishing secure communication channels, particularly within virtual private network (VPN) configurations. The vulnerability stems from insufficient input validation mechanisms within the IKEv1 processing logic, which fails to properly handle malformed or crafted packets that violate expected protocol structures. The affected implementations demonstrate a lack of robust error handling and packet parsing routines that should validate the integrity and format of incoming IKE messages before processing them.
The technical flaw manifests when remote attackers send specially crafted IKE packets that contain malformed data structures or violate protocol specifications within the IKEv1 message format. These malformed packets exploit weaknesses in the parser logic that handles ISAKMP (Internet Security Association and Key Management Protocol) messages, specifically targeting the initial phase of IKE negotiation where security associations are established. The vulnerability operates at the network protocol layer, leveraging the fundamental trust model of IKEv1 where legitimate packets are expected to conform to strict formatting requirements. When these requirements are not properly validated, the implementation becomes susceptible to buffer overflows, memory corruption, or state machine disruptions that lead to system instability.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the entire security infrastructure of affected networks. Device resets caused by these malformed packets can result in complete service outages for VPN connectivity, forcing network administrators to manually restart affected systems and potentially disrupting business operations. The attack vector is particularly concerning because it requires no authentication credentials and can be executed remotely over the network, making it accessible to any attacker with network access to the vulnerable devices. This vulnerability directly impacts the availability aspect of the CIA triad, as it can be exploited to deny legitimate users access to network resources through systematic device resets.
Cisco's advisory documentation for this vulnerability was notably sparse, creating ambiguity about its relationship with other related CVEs including CVE-2005-3666, CVE-2005-3667, and CVE-2005-3668, which suggests overlapping or interconnected weaknesses within the IKEv1 implementation. The lack of detailed technical specifications in the original advisory makes it challenging for security professionals to fully assess the scope of potential exploitation methods and the precise conditions under which these vulnerabilities manifest. This vulnerability aligns with CWE-129, which addresses improper validation of input boundaries, and represents a classic example of how protocol implementation flaws can lead to denial of service conditions. The attack pattern follows techniques described in the MITRE ATT&CK framework under the T1499 sub-technique for network denial of service, where adversaries exploit weaknesses in network protocols to disrupt service availability.
Mitigation strategies should focus on implementing immediate network segmentation to isolate vulnerable devices, applying Cisco's security patches and updates as soon as they become available, and configuring firewalls to filter malformed IKE traffic at network boundaries. Network administrators should also consider implementing monitoring solutions that can detect unusual patterns of IKE packet exchanges that may indicate exploitation attempts. The recommended approach includes disabling IKEv1 where possible and migrating to IKEv2 implementations that offer improved security features and better handling of malformed packets. Additionally, regular vulnerability assessments should be conducted to identify other potential weaknesses in the network infrastructure that could be exploited in similar fashion, as this vulnerability demonstrates the importance of robust input validation in security-critical protocol implementations.