CVE-2026-63911 xfrm: iptfs: reset runtime state when cloning SAs
A use-after-free vulnerability in the Linux kernel's IPTFS module allows attackers to cause denial of service or potentially execute code via crafted network packets.
- 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-2026-63911?
CVE-2026-63911 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:
xfrm: iptfs: reset runtime state when cloning SAs
iptfs_clone_state() clones the IPTFS mode data with kmemdup(). This copies runtime objects which must not be shared with the original SA, including the embedded sk_buff_head, hrtimers, spinlock, and in-flight reassembly/reorder state.
If xfrm_state_migrate() fails after clone_state() but before the later init_state() call has reinitialized those fields, the cloned state can be destroyed by xfrm_state_gc_task() with list and timer state copied from the original SA. With queued packets this lets the clone splice and free skbs owned by the original IPTFS queue, leading to use-after-free and double-free reports in iptfs_destroy_state() and skb release paths.
Reinitialize the clone's runtime state before publishing it through x->mode_data. Because clone_state() now publishes a destroyable mode_data object before init_state(), take the mode callback module reference there. Avoid taking it again from __iptfs_init_state() for the same object.
Which versions are affected by CVE-2026-63911?
How do I fix CVE-2026-63911?
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-2026-63911 being exploited?
There is no known exploitation of CVE-2026-63911 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-63911, DEBIAN-CVE-2026-63911, GHSA-3gc2-w5w2-ffch, UBUNTU-CVE-2026-63911.