CVE-2026-63829 net: ip_gre: require CAP_NET_ADMIN in the device netns for changelink
Attackers with limited network namespace privileges can modify GRE tunnels in other namespaces due to missing capability checks.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-63829?
CVE-2026-63829 is a high-severity missing authorization vulnerability in Linux kernel, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
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: CWE-862
Which versions are affected by CVE-2026-63829?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-63829?
Apply the vendor's patch.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-63829 being exploited?
There is no known exploitation of CVE-2026-63829 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-92588, BELL-CVE-2026-63829, DEBIAN-CVE-2026-63829, GHSA-6wc5-2mjj-pmr6, ROOT-OS-DEBIAN-11-CVE-2026-63829, ROOT-OS-DEBIAN-12-CVE-2026-63829 and 2 more.