# CVE-2026-72347: netfilter: xt_connmark: reject invalid shift parameters

> A local attacker can cause a kernel crash or undefined behavior by installing a netfilter rule with invalid shift parameters in the connmark target.

- **Severity:** High 7.3 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/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:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** BELL-CVE-2026-72347, DEBIAN-CVE-2026-72347, GHSA-5j52-34gv-x96c, UBUNTU-CVE-2026-72347

## What is CVE-2026-72347?

CVE-2026-72347 is a high-severity vulnerability in Linux, published on 15 Aug 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: xt_connmark: reject invalid shift parameters

Revision 2 of the CONNMARK target accepts user-controlled shift
parameters and applies them to 32-bit mark values in
connmark_tg_shift().

A shift_bits value of 32 or more triggers an undefined-shift bug when
the rule is evaluated. Invalid shift_dir values are also accepted and
silently fall back to the left-shift path.

Reject invalid revision-2 shift parameters in connmark_tg_check() so
malformed rules fail at installation time, before they can reach the
packet path.

## Which versions are affected by CVE-2026-72347?


## How do I fix CVE-2026-72347?

Apply the vendor's patch.

## Is CVE-2026-72347 being exploited?

There is no known exploitation of CVE-2026-72347 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72347 and fix it if it is affected.

What it is: CVE-2026-72347 is a high-severity vulnerability in Linux, published on 15 Aug 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-2026-72347 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-2026-72347/ (Markdown: https://insights.sbomify.com/CVE-2026-72347/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72347
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72347
- OSV: https://osv.dev/vulnerability/CVE-2026-72347

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72347/
Summaries are generated and may contain mistakes; the official description above is the record.