CVE-2006-6263 in Teredo
Summary
by MITRE
Teredo clients, when source routing is enabled, recognize a Routing header in an encapsulated IPv6 packet and send the packet to the next hop, which might allow remote attackers to bypass policies of certain Internet gateways that drop all source-routed packets.
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Analysis
by VulDB Data Team • 09/26/2017
The vulnerability described in CVE-2006-6263 relates to the Teredo protocol implementation in IPv6 networking, specifically concerning source routing behavior within encapsulated packets. Teredo is a tunneling mechanism designed to provide IPv6 connectivity for hosts behind NAT devices, allowing them to communicate with native IPv6 networks. When source routing is enabled on Teredo clients, these systems process Routing headers present in encapsulated IPv6 packets by forwarding them to the next hop in the network path. This behavior creates a significant security gap because it effectively bypasses network policies that are specifically designed to drop packets containing source routing information, which is a well-known security risk in network communications.
The technical flaw stems from the Teredo client's misinterpretation of Routing headers within encapsulated packets, where the client acts as a forwarding agent rather than properly validating or rejecting source-routed traffic. This processing behavior violates fundamental network security principles and represents a deviation from standard IPv6 packet handling procedures. The vulnerability manifests when Teredo clients encounter IPv6 packets with Routing headers that have been encapsulated for transmission through the Teredo tunnel. Instead of dropping these packets or properly handling the source routing information, the client forwards them to the next hop in the routing path, thereby enabling attackers to exploit this behavior to circumvent network security controls.
The operational impact of this vulnerability is substantial for network administrators and security professionals managing internet gateways and firewalls. When certain Internet gateways are configured to drop all source-routed packets as part of their security policy, the Teredo client's behavior allows attackers to bypass these protections entirely. This creates a scenario where malicious actors can inject source-routed packets through Teredo clients that are not properly configured or secured, potentially leading to unauthorized network access, routing manipulation, or other attacks that rely on bypassing source routing restrictions. The vulnerability essentially provides a backdoor mechanism that undermines the security posture of networks that depend on source routing filtering as a protective measure.
This vulnerability aligns with CWE-113, which addresses "Improper Neutralization of Special Elements in Output Used by a Downstream Component," and represents a specific implementation flaw in how Teredo clients process Routing headers. The behavior also maps to ATT&CK technique T1071.004, which covers "Application Layer Protocol: DNS," though in this case it's more accurately related to protocol tunneling and network layer manipulation. The security implications extend beyond simple bypassing of packet filtering, as this vulnerability can enable more sophisticated attacks such as routing table manipulation, network reconnaissance, or creating false routing paths that could be exploited for man-in-the-middle attacks. Network security solutions that rely on source routing detection and filtering mechanisms become ineffective against this vulnerability, potentially exposing entire network segments to unauthorized access and manipulation.
The recommended mitigations include disabling source routing functionality on Teredo clients when it is not strictly necessary for network operation, implementing proper network segmentation to isolate Teredo-enabled systems, and ensuring that network gateways are properly configured to detect and block Teredo traffic at the network perimeter. Organizations should also consider updating their network security policies to address the specific behaviors of Teredo implementations and ensure that source routing restrictions are enforced at multiple layers of the network infrastructure. Regular network monitoring and anomaly detection should be implemented to identify unusual Teredo traffic patterns that might indicate exploitation attempts. Additionally, system administrators should review and test their network security configurations to ensure that source routing restrictions are properly enforced even in the presence of Teredo clients, and consider implementing network access controls that specifically target Teredo tunneling protocols to prevent unauthorized use of the vulnerability.