# CVE-2026-72250: netfilter: nf_conntrack_reasm: guard mac_header adjustment after IPv6 defrag

> A missing guard in Linux kernel IPv6 defragmentation causes an invalid MAC header offset, leading to potential kernel crashes or memory corruption.

- **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:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** BELL-CVE-2026-72250, DEBIAN-CVE-2026-72250, GHSA-9f37-2xqv-pf7f, UBUNTU-CVE-2026-72250

## What is CVE-2026-72250?

CVE-2026-72250 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: nf_conntrack_reasm: guard mac_header adjustment after IPv6 defrag

nf_ct_frag6_reasm() slides the packet head forward to drop the IPv6
fragment header and then unconditionally advances skb->mac_header:

	skb->mac_header += sizeof(struct frag_hdr);

On the NF_INET_LOCAL_OUT defrag path the skb has no link-layer header
yet, so skb->mac_header is still the "not set" sentinel (u16)~0U. Adding
sizeof(struct frag_hdr) wraps it to a small value (0xffff + 8 == 7),
after which skb_mac_header_was_set() wrongly reports a MAC header is
present and skb_mac_header() points into the headroom.

The reassembler has done this unconditional add since it was introduced;
it was harmless while mac_header was a bare pointer, but wrong once
mac_header became a u16 offset whose unset state is the ~0U sentinel
tested by skb_mac_header_was_set(). The sibling net/ipv6/reassembly.c
does the same relocation and does guard the adjustment; mirror the
guard here.

## Which versions are affected by CVE-2026-72250?


## How do I fix CVE-2026-72250?

Apply the vendor's patch.

## Is CVE-2026-72250 being exploited?

There is no known exploitation of CVE-2026-72250 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72250 and fix it if it is affected.

What it is: CVE-2026-72250 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-2026-72250 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-2026-72250/ (Markdown: https://insights.sbomify.com/CVE-2026-72250/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72250
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72250
- OSV: https://osv.dev/vulnerability/CVE-2026-72250

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72250/
Summaries are generated and may contain mistakes; the official description above is the record.