Linux Kernel CAP_NET_ADMIN Requirement Vulnerability in IP GRE Tunnel Change Link

A vulnerability exists in the Linux kernel's handling of IP GRE tunnels, specifically in the change link operation. The issue arises because the operation only verifies the CAP_NET_ADMIN privilege against the network namespace of the device being modified, not the namespace of the tunnel itself. This oversight allows a privileged caller to alter a tunnel in a different namespace without the necessary permissions. The vulnerability affects the Linux kernel stable tree.

Impact

Exploitation of this vulnerability could lead to unauthorized modifications of IP GRE tunnel configurations, potentially disrupting network traffic or causing other unintended consequences.

Reproduction

To reproduce this vulnerability, create an IP GRE tunnel and move it to a different network namespace. Then, use a privileged account to initiate a change link operation on the tunnel from the original namespace. The operation will succeed, allowing unauthorized modifications to the tunnel's configuration.

Remediation

Users can upgrade to the latest version of the Linux kernel, where this vulnerability has been addressed.