CVE-2026-53240 xfrm: iptfs: fix use-after-free on first_skb in __input_process_payload
A use-after-free in the Linux kernel's xfrm iptfs module allows attackers to execute arbitrary code or cause a denial of service via race conditions.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-53240?
CVE-2026-53240 is a high-severity use after free vulnerability in Linux kernel, published on 25 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
xfrm: iptfs: fix use-after-free on first_skb in __input_process_payload
__input_process_payload() stores first_skb into xtfs->ra_newskb under drop_lock when starting partial reassembly, then unlocks and breaks out of the processing loop. The post-loop check reads xtfs->ra_newskb without the lock to decide whether first_skb is still owned:
if (first_skb && first_iplen && !defer && first_skb != xtfs->ra_newskb)
Between spin_unlock and this read, a concurrent CPU running iptfs_reassem_cont() (or the drop_timer hrtimer) can complete reassembly, NULL xtfs->ra_newskb, and free the skb. The check then evaluates first_skb != NULL as true, and pskb_trim/ip_summed/consume_skb operate on the freed skb — a use-after-free in skbuff_head_cache.
Replace the unlocked read with a local bool that records whether first_skb was handed to the reassembly state in the current call. The flag is set after the existing spin_unlock, before the break, using the pointer equality that is stable at that point (first_skb == skb iff first_skb was stored in ra_newskb).
Weakness: CWE-416
Which versions are affected by CVE-2026-53240?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-53240?
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-2026-53240 being exploited?
There is no known exploitation of CVE-2026-53240 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-53240, DEBIAN-CVE-2026-53240, GHSA-5m64-3x43-vxjx, UBUNTU-CVE-2026-53240.