# CVE-2026-90072: net/sched: sfq: clamp quantum to avoid signed overflow soft lockup

> A local attacker with CAP_NET_ADMIN can cause a kernel soft lockup by configuring a network device with an excessively large MTU, leading to a denial of service.

- **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-102920, BELL-CVE-2026-90072, DEBIAN-CVE-2026-90072, GHSA-783h-5cfx-mm7x, UBUNTU-CVE-2026-90072

## What is CVE-2026-90072?

CVE-2026-90072 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: sfq: clamp quantum to avoid signed overflow soft lockup

sfq_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) (unsigned). A
device with a huge MTU (e.g. dummy with max_mtu == 0 accepting MTU
2147483634) makes psched_mtu() return 0x80000000, so slot->allot = INT_MIN
and INT_MIN + INT_MIN toggles between INT_MIN and 0 forever, spinning
sfq_dequeue() under the qdisc lock.

Clamp the quantum to [256, 1 << 20] so the refill loop terminates. The
lower bound also covers q->quantum == 0 (psched_mtu() returning 0),
which spins sfq_dequeue() identically. sfq_change() already rejects a
negative quantum, so only the init path was exposed.

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-2026-90072?


## How do I fix CVE-2026-90072?

Apply the vendor's patch.

## Is CVE-2026-90072 being exploited?

There is no known exploitation of CVE-2026-90072 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90072 and fix it if it is affected.

What it is: CVE-2026-90072 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-2026-90072 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-2026-90072/ (Markdown: https://insights.sbomify.com/CVE-2026-90072/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90072
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90072
- OSV: https://osv.dev/vulnerability/CVE-2026-90072

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90072/
Summaries are generated and may contain mistakes; the official description above is the record.