# CVE-2026-45859: netfilter: nfnetlink_queue: do shared-unconfirmed check before segmentation

> A regression in the Linux kernel netfilter module causes UDP packets to be dropped instead of queued, leading to denial of service.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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:** 27 May 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-88478, BELL-CVE-2026-45859, DEBIAN-CVE-2026-45859, GHSA-v8w5-25mx-q5r4, ROOT-OS-DEBIAN-12-CVE-2026-45859, ROOT-OS-UBUNTU-2204-CVE-2026-45859, ROOT-OS-UBUNTU-2404-CVE-2026-45859, UBUNTU-CVE-2026-45859

## What is CVE-2026-45859?

CVE-2026-45859 is a high-severity denial of service vulnerability in Linux kernel, published on 27 May 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: nfnetlink_queue: do shared-unconfirmed check before segmentation

Ulrich reports a regression with nfqueue:

If an application did not set the 'F_GSO' capability flag and a gso
packet with an unconfirmed nf_conn entry is received all packets are
now dropped instead of queued, because the check happens after
skb_gso_segment().  In that case, we did have exclusive ownership
of the skb and its associated conntrack entry.  The elevated use
count is due to skb_clone happening via skb_gso_segment().

Move the check so that its peformed vs. the aggregated packet.

Then, annotate the individual segments except the first one so we
can do a 2nd check at reinject time.

For the normal case, where userspace does in-order reinjects, this avoids
packet drops: first reinjected segment continues traversal and confirms
entry, remaining segments observe the confirmed entry.

While at it, simplify nf_ct_drop_unconfirmed(): We only care about
unconfirmed entries with a refcnt > 1, there is no need to special-case
dying entries.

This only happens with UDP.  With TCP, the only unconfirmed packet will
be the TCP SYN, those aren't aggregated by GRO.

Next patch adds a udpgro test case to cover this scenario.

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-45859?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-45859?

Apply the vendor's patch.

## Is CVE-2026-45859 being exploited?

There is no known exploitation of CVE-2026-45859 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-2026-45859 and fix it if it is affected.

What it is: CVE-2026-45859 is a high-severity denial of service vulnerability in Linux kernel, published on 27 May 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-2026-45859 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-2026-45859/ (Markdown: https://insights.sbomify.com/CVE-2026-45859/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45859
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45859
- OSV: https://osv.dev/vulnerability/CVE-2026-45859

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-45859/
Summaries are generated and may contain mistakes; the official description above is the record.