# CVE-2026-43036: net: use skb_header_pointer() for TCPv4 GSO frag_off check

> A Linux kernel vulnerability allows reading uninitialized memory during TCPv4 GSO checks, potentially disclosing sensitive kernel data to local attackers.

- **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:** 1 May 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-85359, BELL-CVE-2026-43036, DEBIAN-CVE-2026-43036, GHSA-wjhp-5p5w-qmhh, ROOT-OS-DEBIAN-11-CVE-2026-43036, ROOT-OS-DEBIAN-12-CVE-2026-43036, ROOT-OS-UBUNTU-2204-CVE-2026-43036, ROOT-OS-UBUNTU-2404-CVE-2026-43036, UBUNTU-CVE-2026-43036

## What is CVE-2026-43036?

CVE-2026-43036 is a medium-severity vulnerability in Linux kernel, published on 1 May 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:

net: use skb_header_pointer() for TCPv4 GSO frag_off check

Syzbot reported a KMSAN uninit-value warning in gso_features_check()
called from netif_skb_features() [1].

gso_features_check() reads iph->frag_off to decide whether to clear
mangleid_features. Accessing the IPv4 header via ip_hdr()/inner_ip_hdr()
can rely on skb header offsets that are not always safe for direct
dereference on packets injected from PF_PACKET paths.

Use skb_header_pointer() for the TCPv4 frag_off check so the header read
is robust whether data is already linear or needs copying.

[1] https://syzkaller.appspot.com/bug?extid=1543a7d954d9c6d00407

Weakness: CWE-908 (Use of Uninitialized Resource)

## Which versions are affected by CVE-2026-43036?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-43036?

Apply the vendor's patch.

## Is CVE-2026-43036 being exploited?

There is no known exploitation of CVE-2026-43036 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-2026-43036 and fix it if it is affected.

What it is: CVE-2026-43036 is a medium-severity vulnerability in Linux kernel, published on 1 May 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-2026-43036 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-2026-43036/ (Markdown: https://insights.sbomify.com/CVE-2026-43036/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43036
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43036
- OSV: https://osv.dev/vulnerability/CVE-2026-43036

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43036/
Summaries are generated and may contain mistakes; the official description above is the record.