# 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.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** Yes
- **Published:** 25 Mar 2026
- **Updated:** 19 Oct 2026
- **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, ROOT-OS-DEBIAN-13-CVE-2026-23351, ROOT-OS-UBUNTU-2204-CVE-2026-23351, ROOT-OS-UBUNTU-2404-CVE-2026-23351, UBUNTU-CVE-2026-23351

## 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 (Use After Free)

## Which versions are affected by CVE-2026-23351?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-23351?

Apply the vendor's patch.

## 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

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-23351 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-23351 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-23351/ (Markdown: https://insights.sbomify.com/CVE-2026-23351/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23351
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23351
- OSV: https://osv.dev/vulnerability/CVE-2026-23351

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23351/
Summaries are generated and may contain mistakes; the official description above is the record.