CVE-2013-3436 in IOS
Summary
by MITRE
The default configuration of the Group Encrypted Transport VPN (GET VPN) feature on Cisco IOS uses an improper mechanism for enabling Group Domain of Interpretation (GDOI) traffic flow, which allows remote attackers to bypass the encryption policy via certain uses of UDP port 848, aka Bug ID CSCui07698.
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Analysis
by VulDB Data Team • 12/26/2024
The vulnerability described in CVE-2013-3436 resides within the Group Encrypted Transport VPN implementation of Cisco IOS operating systems, specifically affecting the Group Domain of Interpretation protocol handling. This weakness manifests in the default configuration settings that govern how GET VPN manages GDOI traffic flows, creating a critical security gap that can be exploited by remote attackers without authentication. The issue stems from the improper mechanism used to enable GDOI traffic, which fundamentally undermines the intended cryptographic protection of VPN communications.
The technical flaw involves the insecure handling of UDP port 848 traffic, which serves as the primary communication channel for GDOI messages within GET VPN implementations. When GET VPN is deployed with default configurations, the system fails to properly validate or authenticate GDOI traffic flows, allowing unauthorized entities to inject malicious packets that bypass the encryption policies. This vulnerability specifically targets the protocol negotiation and key management aspects of the VPN framework, where the system should enforce strict authentication and encryption requirements but instead permits traffic flow that circumvents these security controls. The flaw operates at the network protocol level, leveraging the inherent trust model of the GDOI protocol to establish unauthorized communication channels.
Operationally, this vulnerability creates a significant risk for organizations relying on Cisco IOS-based devices for secure communications, as it allows remote attackers to establish unauthorized encrypted tunnels that appear legitimate to the network infrastructure. The impact extends beyond simple data interception, as attackers can potentially manipulate traffic flows, inject malicious data, or establish persistent backdoors within the network. The vulnerability affects the fundamental integrity of the VPN security model, enabling attackers to bypass encryption policies that should protect sensitive communications. Network administrators face the challenge of detecting unauthorized GDOI traffic flows while maintaining legitimate VPN operations, as the malicious traffic can appear normal to standard monitoring tools.
Organizations should implement immediate mitigations including disabling unused GDOI functionality, configuring explicit access control lists to restrict UDP port 848 traffic, and ensuring proper authentication mechanisms are enforced for all GDOI communications. The recommended approach involves modifying default configurations to enforce stricter validation of GDOI traffic sources and implementing network segmentation to limit exposure. Additionally, regular monitoring of GDOI traffic patterns should be established to detect anomalous behavior indicative of exploitation attempts. This vulnerability aligns with CWE-284 Access Control Issues and maps to ATT&CK technique T1071.004 Application Layer Protocol: DNS, as it involves improper access control within application layer protocols. Organizations should also consider implementing network behavior analysis tools to detect the subtle indicators of GDOI traffic manipulation that may occur during exploitation attempts.