IPv6-in-IPv4 Tunneling Vulnerability Allows Traffic Spoofing and Routing via Exposed Interfaces

A vulnerability exists in the IPv6-in-IPv4 tunneling mechanism, as defined in RFC 4213, allowing an attacker to spoof and route traffic through a vulnerable host's network interface. This issue arises because the tunneling protocol lacks authentication, enabling the injection of traffic from any source. The vulnerability is present in hosts that accept unencrypted tunneling packets without verifying the sender's identity, effectively turning the host into a one-way proxy for the attacker.

Impact

Exploitation of this vulnerability allows for source address spoofing, where an attacker can send packets that appear to come from a trusted source, bypassing network filters. This can lead to unauthorized access to private networks, where tunneled packets can be used to gather information or launch further attacks. Additionally, the vulnerability can be exploited to perform denial-of-service attacks, amplifying traffic by looping packets between vulnerable hosts or draining a host's outgoing bandwidth.

Reproduction

The vulnerability can be reproduced by sending IPv6 packets encapsulated in IPv4 packets to a host that accepts such traffic without authentication. The outer IPv4 header can be spoofed to include the attacker's IP address as the source and the vulnerable host's IP as the destination. Once the packet is received, the host will strip the outer header and forward the inner packet, effectively routing traffic as if it originated from the vulnerable host.

Remediation

To address this vulnerability, hosts should be configured to only accept tunneling packets from trusted sources. Additionally, using more secure tunneling protocols that include authentication and encryption, such as IPsec or WireGuard, is recommended.