# CVE-2026-90073: net/sched: hhf: clamp quantum before hhf_change() to avoid overflow

> A local attacker with CAP_NET_ADMIN can cause a kernel denial of service via integer overflow in the HHF qdisc when using devices with huge MTUs.

- **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-102557, BELL-CVE-2026-90073, DEBIAN-CVE-2026-90073, GHSA-xxq9-2g6r-mm98, UBUNTU-CVE-2026-90073

## What is CVE-2026-90073?

CVE-2026-90073 is a 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:

net/sched: hhf: clamp quantum before hhf_change() to avoid overflow

hhf_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) with no overflow
check. A device with a huge MTU (e.g. dummy with max_mtu == 0 accepting
MTU 2147483634) makes weight * quantum overflow the signed deficit in
hhf_dequeue(), spinning forever.

Clamp q->quantum before hhf_change() so both the opt and !opt paths see
a sane quantum. Without this, bare "tc qdisc add ... hhf" succeeds with
a clamped quantum but "tc qdisc add ... hhf limit 1000" (any option
present) fails with -EINVAL because hhf_change() re-validates the
unclamped default (sch_hhf.c:559). 256 matches fq_codel's floor and is
a sane minimum for a DRR quantum.

Conditions to recreate the bug: a device whose MTU (plus
hard_header_len) wraps psched_mtu() into the sign bit (e.g. a dummy
device with max_mtu == 0 accepting MTU 2147483634). Requires
CAP_NET_ADMIN in a user namespace.

## Which versions are affected by CVE-2026-90073?


## How do I fix CVE-2026-90073?

Apply the vendor's patch.

## Is CVE-2026-90073 being exploited?

There is no known exploitation of CVE-2026-90073 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90073 and fix it if it is affected.

What it is: CVE-2026-90073 is a 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-2026-90073 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-2026-90073/ (Markdown: https://insights.sbomify.com/CVE-2026-90073/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90073
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90073
- OSV: https://osv.dev/vulnerability/CVE-2026-90073

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90073/
Summaries are generated and may contain mistakes; the official description above is the record.