CVE-2026-63917 ip6: vti: Use ip6_tnl.net in vti6_changelink().
A use-after-free in the Linux kernel's IPv6 VTI tunnel handling allows local attackers to cause a system crash or potentially escalate privileges via network namespace manipulation.
- 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-2026-63917?
CVE-2026-63917 is a high-severity use after free vulnerability in Linux, 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:
ip6: vti: Use ip6_tnl.net in vti6_changelink().
ip netns add ns1 ip netns add ns2 ip -n ns1 link add vti6_test type vti6 remote ::1 local ::2 key 7 ip -n ns1 link set vti6_test netns ns2 ip -n ns2 link set vti6_test type vti6 remote ::3 local ::4 key 9 ip netns del ns2 ip netns del ns1 [ 132.495484] ------------[ cut here ]------------ [ 132.497609] kernel BUG at net/core/dev.c:12376!
Commit 61220ab34948 ("vti6: Enable namespace changing") dropped NETIF_F_NETNS_LOCAL from vti6 devices. A vti6 tunnel can then move through IFLA_NET_NS_FD. After the move dev_net(dev) points at the new netns while t->net stays at the creation netns.
vti6_changelink() and vti6_update() still use dev_net(dev) and dev_net(t->dev). They unlink from one per netns hash and relink into another. The creation netns is left with a stale entry. cleanup_net() of that netns later walks freed memory.
Reachable from an unprivileged user namespace (unshare --user --map-root-user --net). Cross tenant scope on container hosts.
Weakness: CWE-416
Which versions are affected by CVE-2026-63917?
How do I fix CVE-2026-63917?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-63917 being exploited?
There is no known exploitation of CVE-2026-63917 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-63917, DEBIAN-CVE-2026-63917, GHSA-225v-7w3r-pcq9, ROOT-OS-UBUNTU-2204-CVE-2026-63917, UBUNTU-CVE-2026-63917.