# CVE-2026-72436: netfilter: ipset: Don't use test_bit() in lockless RCU readers in hash types

> A race condition in Linux kernel ipset hash types due to missing memory barriers in lockless RCU readers could lead to undefined behavior.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** BELL-CVE-2026-72436, DEBIAN-CVE-2026-72436, GHSA-6x4x-6p4p-6f5f, UBUNTU-CVE-2026-72436

## What is CVE-2026-72436?

CVE-2026-72436 is a critical vulnerability in Linux, published on 15 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

netfilter: ipset: Don't use test_bit() in lockless RCU readers in hash types

Sashiko pointed out that there are a few lockless RCU readers
using test_bit() which is a relaxed atomic operation and
provides no memory barrier guarantees. Use test_bit_acquire()
instead where the operation may run parallel with add/del/gc,
i.e. is not one from the next cases

- protected by region lock
- in a set destroy phase
- in a new/temporary set creation phase

## Which versions are affected by CVE-2026-72436?


## How do I fix CVE-2026-72436?

Apply the vendor's patch.

## Is CVE-2026-72436 being exploited?

There is no known exploitation of CVE-2026-72436 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72436 and fix it if it is affected.

What it is: CVE-2026-72436 is a critical vulnerability in Linux, published on 15 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-72436 in the wild and no public exploit code.

Affected product: Linux. 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-2026-72436/ (Markdown: https://insights.sbomify.com/CVE-2026-72436/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72436
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72436
- OSV: https://osv.dev/vulnerability/CVE-2026-72436

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72436/
Summaries are generated and may contain mistakes; the official description above is the record.