# CVE-2026-98570: net: ipv6: keep room for the mac header in dst_dev_overhead()

> A memory corruption vulnerability in the Linux kernel IPv6 stack allows remote attackers to cause denial of service or execute code via crafted network traffic.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-109086, BELL-CVE-2026-98570, DEBIAN-CVE-2026-98570, GHSA-4prh-wfp5-28j7, UBUNTU-CVE-2026-98570

## What is CVE-2026-98570?

CVE-2026-98570 is a memory corruption vulnerability in Linux, published on 18 Oct 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:

net: ipv6: keep room for the mac header in dst_dev_overhead()

The seg6, ioam6 and rpl lwtunnels size their skb_cow_head() request as
the length they are about to push plus dst_dev_overhead(), then push the
new headers and rebuild the mac header below them with
skb_mac_header_rebuild().  That rebuild needs skb->mac_len of headroom,
but dst_dev_overhead() leaves LL_RESERVED_SPACE() of the egress device,
16 bytes for plain Ethernet.

Where the mac header is longer than that, as it is on ingress through a
VLAN device with reorder_hdr off, the rebuild runs out of room:
skb_set_mac_header(skb, -skb->mac_len) computes a negative offset,
stores it unchecked in the u16 skb->mac_header, and the memmove that
follows writes skb->mac_len bytes about 64 KB past skb->head.
Forwarding plain ping6 traffic through such a device reproduces it on
all five seg6 encapsulation modes and on the rpl and ioam6 inline paths;
skb->mac_header comes back as 65534 on a 704-byte head.

Return the larger of the two.  The helper already returns skb->mac_len
when it has no dst, so this only makes the other branch agree, and it
covers every caller rather than each call site in turn.

## Which versions are affected by CVE-2026-98570?


## How do I fix CVE-2026-98570?

Apply the vendor's patch.

## Is CVE-2026-98570 being exploited?

There is no known exploitation of CVE-2026-98570 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98570 and fix it if it is affected.

What it is: CVE-2026-98570 is a memory corruption vulnerability in Linux, published on 18 Oct 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-2026-98570 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-2026-98570/ (Markdown: https://insights.sbomify.com/CVE-2026-98570/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98570
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98570
- OSV: https://osv.dev/vulnerability/CVE-2026-98570

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98570/
Summaries are generated and may contain mistakes; the official description above is the record.