CVE-2026-63829

In the Linux kernel, the following vulnerability has been resolved:

net: ip_gre: require CAP_NET_ADMIN in the device netns for changelink

A tunnel changelink() operates on at most two netns, dev_net(dev) and the tunnel link netns t->net. They differ once the device is created in or moved to a netns other than the one the request runs in. The rtnl changelink path checks CAP_NET_ADMIN only against dev_net(dev), so a caller privileged there but not in t->net can rewrite a tunnel that lives in t->net.

Add rtnl_dev_link_net_capable() next to rtnl_get_net_ns_capable() in net/core/rtnetlink.c. It requires CAP_NET_ADMIN in the link netns and is skipped when the link netns is dev_net(dev), where the rtnl path already checked it. The other patches in this series use the same helper.

Gate ipgre_changelink() and erspan_changelink() with it, at the top of the op before any attribute is parsed, because the parsers update live tunnel fields first. ipgre_netlink_parms() sets t->collect_md before ip_tunnel_changelink() runs.

Commit 8b484efd5cb4 (ip6: vti: Use ip6_tnl.net in vti6_siocdevprivate().) added the same check on the ioctl path. This adds it on RTM_NEWLINK.

Weakness

The product does not perform an authorization check when an actor attempts to access a resource or perform an action.

Affected Software

Potential Mitigations

• Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) [REF-229] to enforce the roles at the appropriate boundaries.
• Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
• Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
• For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
• For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page.
• One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/665.html

References

• https://git.kernel.org/stable/c/1697957eb0971d420dde42862b88eb43506a1105
• https://git.kernel.org/stable/c/19275943d8fe903eb7b9aa53e380e41efd042ada
• https://git.kernel.org/stable/c/47b5d3d506609b08b2e1f7c14f0b681a1953d572
• https://git.kernel.org/stable/c/8165f7ff57d9667d2bb477ef6af83ede7fed4ad7
• https://git.kernel.org/stable/c/866b0f5ae599490bd496fd84581c68ac8b94e6af
• https://git.kernel.org/stable/c/92b766fc55156e0da2ecd0c2302c971118f8a229
• https://git.kernel.org/stable/c/9831bc9ecb402957810c2045c663fbfe9b09e296
• https://git.kernel.org/stable/c/e54c05ed3d9c28733fb9e5837219aca3691defa3