# CVE-2026-72400: seg6: validate SRH length before reading fixed fields

> A missing length check in the Linux kernel's SEG6 validation allows out-of-bounds reads via BPF, potentially causing a denial of service.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** BELL-CVE-2026-72400, DEBIAN-CVE-2026-72400, GHSA-x2wv-639g-pv5q, UBUNTU-CVE-2026-72400

## What is CVE-2026-72400?

CVE-2026-72400 is a high-severity vulnerability in Linux, published on 15 Aug 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:

seg6: validate SRH length before reading fixed fields

seg6_validate_srh() reads fixed SRH fields such as srh->type and
srh->hdrlen before checking that the supplied length covers the fixed
struct ipv6_sr_hdr fields.

The BPF SEG6 encap path reaches this with a BPF program-supplied pointer
and length: bpf_lwt_push_encap() and the SEG6 local BPF END_B6 and
END_B6_ENCAP actions call bpf_push_seg6_encap(), which forwards the
length to seg6_validate_srh() with no minimum-size guard.  A 2-byte SEG6
encap header can therefore make the validator read srh->type at offset 2
beyond the caller-supplied buffer.

Reject lengths shorter than the fixed SRH at the top of
seg6_validate_srh(), before any field is read.  This fixes the BPF helper
path and keeps the common validator robust.

## Which versions are affected by CVE-2026-72400?


## How do I fix CVE-2026-72400?

Apply the vendor's patch.

## Is CVE-2026-72400 being exploited?

There is no known exploitation of CVE-2026-72400 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72400 and fix it if it is affected.

What it is: CVE-2026-72400 is a high-severity vulnerability in Linux, published on 15 Aug 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-2026-72400 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-2026-72400/ (Markdown: https://insights.sbomify.com/CVE-2026-72400/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72400
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72400
- OSV: https://osv.dev/vulnerability/CVE-2026-72400

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72400/
Summaries are generated and may contain mistakes; the official description above is the record.