CVE-2026-23351 netfilter: nft_set_pipapo: split gc into unlink and reclaim phase
A use-after-free in the Linux kernel netfilter pipapo set type allows local attackers to cause a denial of service via soft lockups or RCU stalls.
- 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-2026-23351?
CVE-2026-23351 is a high-severity use after free vulnerability in Linux kernel, published on 25 Mar 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:
netfilter: nft_set_pipapo: split gc into unlink and reclaim phase
Yiming Qian reports Use-after-free in the pipapo set type: Under a large number of expired elements, commit-time GC can run for a very long time in a non-preemptible context, triggering soft lockup warnings and RCU stall reports (local denial of service).
We must split GC in an unlink and a reclaim phase.
We cannot queue elements for freeing until pointers have been swapped. Expired elements are still exposed to both the packet path and userspace dumpers via the live copy of the data structure.
call_rcu() does not protect us: dump operations or element lookups starting after call_rcu has fired can still observe the free'd element, unless the commit phase has made enough progress to swap the clone and live pointers before any new reader has picked up the old version.
This a similar approach as done recently for the rbtree backend in commit 35f83a75529a ("netfilter: nft_set_rbtree: don't gc elements on insert").
Weakness: CWE-416
Which versions are affected by CVE-2026-23351?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-23351?
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-2026-23351 being exploited?
There is no known exploitation of CVE-2026-23351 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-80670, BELL-CVE-2026-23351, DEBIAN-CVE-2026-23351, GHSA-42q3-4jmh-pwqx, ROOT-OS-DEBIAN-11-CVE-2026-23351, ROOT-OS-DEBIAN-12-CVE-2026-23351 and 4 more.