# CVE-2026-43038: ipv6: icmp: clear skb2->cb[] in ip6_err_gen_icmpv6_unreach()

> A memory corruption vulnerability in the Linux kernel IPv6 ICMP handling allows attackers to trigger out-of-bounds writes via forged ICMPv4 errors, potentially leading to code execution or system crashes.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:** 1 May 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-43038, DEBIAN-CVE-2026-43038, GHSA-78m7-4xgc-xrrq, ROOT-OS-DEBIAN-11-CVE-2026-43038, ROOT-OS-UBUNTU-2204-CVE-2026-43038, ROOT-OS-UBUNTU-2404-CVE-2026-43038, UBUNTU-CVE-2026-43038

## What is CVE-2026-43038?

CVE-2026-43038 is a critical memory corruption vulnerability in Linux kernel, published on 1 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:

ipv6: icmp: clear skb2->cb[] in ip6_err_gen_icmpv6_unreach()

Sashiko AI-review observed:

  In ip6_err_gen_icmpv6_unreach(), the skb is an outer IPv4 ICMP error packet
  where its cb contains an IPv4 inet_skb_parm. When skb is cloned into skb2
  and passed to icmp6_send(), it uses IP6CB(skb2).

  IP6CB interprets the IPv4 inet_skb_parm as an inet6_skb_parm. The cipso
  offset in inet_skb_parm.opt directly overlaps with dsthao in inet6_skb_parm
  at offset 18.

  If an attacker sends a forged ICMPv4 error with a CIPSO IP option, dsthao
  would be a non-zero offset. Inside icmp6_send(), mip6_addr_swap() is called
  and uses ipv6_find_tlv(skb, opt->dsthao, IPV6_TLV_HAO).

  This would scan the inner, attacker-controlled IPv6 packet starting at that
  offset, potentially returning a fake TLV without checking if the remaining
  packet length can hold the full 18-byte struct ipv6_destopt_hao.

  Could mip6_addr_swap() then perform a 16-byte swap that extends past the end
  of the packet data into skb_shared_info?

  Should the cb array also be cleared in ip6_err_gen_icmpv6_unreach() and
  ip6ip6_err() to prevent this?

This patch implements the first suggestion.

I am not sure if ip6ip6_err() needs to be changed.
A separate patch would be better anyway.

Weakness: CWE-843 (Access of Resource Using Incompatible Type), CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-43038?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-43038?

Apply the vendor's patch.

## Is CVE-2026-43038 being exploited?

There is no known exploitation of CVE-2026-43038 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-2026-43038 and fix it if it is affected.

What it is: CVE-2026-43038 is a critical memory corruption vulnerability in Linux kernel, published on 1 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-2026-43038 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-2026-43038/ (Markdown: https://insights.sbomify.com/CVE-2026-43038/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43038
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43038
- OSV: https://osv.dev/vulnerability/CVE-2026-43038

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43038/
Summaries are generated and may contain mistakes; the official description above is the record.