# CVE-2026-100070: netfilter: nf_nat_sip: rewind offset when NAT shrinks the packet

> A flaw in Linux kernel netfilter SIP NAT handling may leak internal network details by skipping Contact headers when packet size changes.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-100070, DEBIAN-CVE-2026-100070, GHSA-hw8v-4xhx-cmhp, UBUNTU-CVE-2026-100070

## What is CVE-2026-100070?

CVE-2026-100070 is a medium-severity vulnerability in Linux kernel, published on 25 Sep 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_nat_sip: rewind offset when NAT shrinks the packet

sashiko says:
 If map_addr() changes the packet length, such as when the public NAT IP
 string is shorter or longer than the internal IP, coff will still point to
 the offset relative to the pre-mangled packet.
 If the packet shrinks, coff could overshoot the correct position,
 potentially causing the next ct_sip_parse_header_uri() call to silently
 skip bytes and miss subsequent Contact headers. Could this lead to a
 failure to NAT those subsequent headers and leak internal network details?

## Which versions are affected by CVE-2026-100070?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-100070?

Apply the vendor's patch.

## Is CVE-2026-100070 being exploited?

There is no known exploitation of CVE-2026-100070 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-2026-100070 and fix it if it is affected.

What it is: CVE-2026-100070 is a medium-severity vulnerability in Linux kernel, published on 25 Sep 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-2026-100070 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-2026-100070/ (Markdown: https://insights.sbomify.com/CVE-2026-100070/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-100070
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-100070
- OSV: https://osv.dev/vulnerability/CVE-2026-100070

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-100070/
Summaries are generated and may contain mistakes; the official description above is the record.