# CVE-2025-38000: sch_hfsc: Fix qlen accounting bug when using peek in hfsc_enqueue()

> A use-after-free vulnerability in the Linux kernel's HFSC scheduler allows attackers to potentially execute code or escalate privileges via inconsistent queue accounting.

- **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:** 6 Jun 2025
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-63684, BELL-CVE-2025-38000, DEBIAN-CVE-2025-38000, GHSA-5fqh-wrrw-3qc9, ROOT-OS-DEBIAN-11-CVE-2025-38000, ROOT-OS-DEBIAN-12-CVE-2025-38000, ROOT-OS-UBUNTU-2204-CVE-2025-38000, UBUNTU-CVE-2025-38000

## What is CVE-2025-38000?

CVE-2025-38000 is a high-severity use after free vulnerability in Debian Debian Linux, published on 6 Jun 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:

sch_hfsc: Fix qlen accounting bug when using peek in hfsc_enqueue()

When enqueuing the first packet to an HFSC class, hfsc_enqueue() calls the
child qdisc's peek() operation before incrementing sch->q.qlen and
sch->qstats.backlog. If the child qdisc uses qdisc_peek_dequeued(), this may
trigger an immediate dequeue and potential packet drop. In such cases,
qdisc_tree_reduce_backlog() is called, but the HFSC qdisc's qlen and backlog
have not yet been updated, leading to inconsistent queue accounting. This
can leave an empty HFSC class in the active list, causing further
consequences like use-after-free.

This patch fixes the bug by moving the increment of sch->q.qlen and
sch->qstats.backlog before the call to the child qdisc's peek() operation.
This ensures that queue length and backlog are always accurate when packet
drops or dequeues are triggered during the peek.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2025-38000?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-38000?

Apply the vendor's patch.

## Is CVE-2025-38000 being exploited?

There is no known exploitation of CVE-2025-38000 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-38000 and fix it if it is affected.

What it is: CVE-2025-38000 is a high-severity use after free vulnerability in Debian Debian Linux, published on 6 Jun 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-2025-38000 in the wild and no public exploit code.

Affected product: Debian Debian 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-2025-38000/ (Markdown: https://insights.sbomify.com/CVE-2025-38000/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-38000
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-38000
- OSV: https://osv.dev/vulnerability/CVE-2025-38000

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-38000/
Summaries are generated and may contain mistakes; the official description above is the record.