# CVE-2025-40083: net/sched: sch_qfq: Fix null-deref in agg_dequeue

> A null pointer dereference in the Linux kernel's QFQ scheduler can cause a system crash, requiring local access and specific network scheduling configuration.

- **Severity:** Not scored
- **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:** 29 Oct 2025
- **Updated:** 16 Jun 2026
- **Also known as:** AZL-69027, BELL-CVE-2025-40083, DEBIAN-CVE-2025-40083, GHSA-wf68-85vc-c49w, ROOT-OS-DEBIAN-11-CVE-2025-40083, ROOT-OS-DEBIAN-12-CVE-2025-40083, ROOT-OS-DEBIAN-13-CVE-2025-40083, ROOT-OS-UBUNTU-2204-CVE-2025-40083, ROOT-OS-UBUNTU-2404-CVE-2025-40083, UBUNTU-CVE-2025-40083

## What is CVE-2025-40083?

CVE-2025-40083 is a vulnerability in Linux, published on 29 Oct 2025. 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: sch_qfq: Fix null-deref in agg_dequeue

To prevent a potential crash in agg_dequeue (net/sched/sch_qfq.c)
when cl->qdisc->ops->peek(cl->qdisc) returns NULL, we check the return
value before using it, similar to the existing approach in sch_hfsc.c.

To avoid code duplication, the following changes are made:

1. Changed qdisc_warn_nonwc(include/net/pkt_sched.h) into a static
inline function.

2. Moved qdisc_peek_len from net/sched/sch_hfsc.c to
include/net/pkt_sched.h so that sch_qfq can reuse it.

3. Applied qdisc_peek_len in agg_dequeue to avoid crashing.

## Which versions are affected by CVE-2025-40083?


## How do I fix CVE-2025-40083?

Apply the vendor's patch.

## Is CVE-2025-40083 being exploited?

There is no known exploitation of CVE-2025-40083 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40083 and fix it if it is affected.

What it is: CVE-2025-40083 is a vulnerability in Linux, published on 29 Oct 2025. 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-2025-40083 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-2025-40083/ (Markdown: https://insights.sbomify.com/CVE-2025-40083/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40083
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40083
- OSV: https://osv.dev/vulnerability/CVE-2025-40083

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40083/
Summaries are generated and may contain mistakes; the official description above is the record.