# CVE-2026-90160: lwt_bpf: Restore reserved headroom after xmit program

> A local attacker with high privileges can cause network packet drops and potential denial of service by exploiting a headroom check flaw in the Linux kernel's LWT BPF implementation.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-102935, BELL-CVE-2026-90160, DEBIAN-CVE-2026-90160, GHSA-p997-jc38-xxh3, UBUNTU-CVE-2026-90160

## What is CVE-2026-90160?

CVE-2026-90160 is a denial of service vulnerability in Linux, published on 17 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:

lwt_bpf: Restore reserved headroom after xmit program

ip_finish_output2() expands an skb to LL_RESERVED_SPACE(dev) before LWT
xmit. An LWT_XMIT BPF program can then modify the skb head and still
return BPF_OK, so bpf_xmit() rechecks the remaining headroom before the
skb continues to neighbour output.

That recheck uses dst->dev->hard_header_len. This is not enough for the
neighbour cached-header path: neigh_hh_output() copies the cached hardware
header using the aligned hh_cache size, HH_DATA_MOD for short headers or
HH_DATA_ALIGN(hh_len) otherwise.

On Ethernet, hard_header_len is 14 but the cached copy needs 16 bytes. If
an LWT_XMIT BPF program calls bpf_skb_change_head(skb, 1, 0), the skb can
still have 15 bytes of headroom after the program. The existing check
accepts that, after which neigh_hh_output() hits its headroom warning and
drops the skb.

Use LL_RESERVED_SPACE(dst->dev) in the post-BPF headroom check to match
the reservation made before LWT xmit.

## Which versions are affected by CVE-2026-90160?


## How do I fix CVE-2026-90160?

Apply the vendor's patch.

## Is CVE-2026-90160 being exploited?

There is no known exploitation of CVE-2026-90160 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90160 and fix it if it is affected.

What it is: CVE-2026-90160 is a denial of service vulnerability in Linux, published on 17 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-2026-90160 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-2026-90160/ (Markdown: https://insights.sbomify.com/CVE-2026-90160/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90160
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90160
- OSV: https://osv.dev/vulnerability/CVE-2026-90160

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90160/
Summaries are generated and may contain mistakes; the official description above is the record.