# CVE-2025-38193: net_sched: sch_sfq: reject invalid perturb period

> An integer overflow in the Linux kernel's SFQ scheduler allows triggering a race condition, potentially leading to 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:** 4 Jul 2025
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-64764, BELL-CVE-2025-38193, DEBIAN-CVE-2025-38193, GHSA-53vw-2fxq-35qf, ROOT-OS-DEBIAN-11-CVE-2025-38193, ROOT-OS-DEBIAN-12-CVE-2025-38193, ROOT-OS-UBUNTU-2204-CVE-2025-38193, ROOT-OS-UBUNTU-2404-CVE-2025-38193, UBUNTU-CVE-2025-38193

## What is CVE-2025-38193?

CVE-2025-38193 is a high-severity vulnerability in Debian Debian Linux, published on 4 Jul 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_sfq: reject invalid perturb period

Gerrard Tai reported that SFQ perturb_period has no range check yet,
and this can be used to trigger a race condition fixed in a separate patch.

We want to make sure ctl->perturb_period * HZ will not overflow
and is positive.

tc qd add dev lo root sfq perturb -10   # negative value : error
Error: sch_sfq: invalid perturb period.

tc qd add dev lo root sfq perturb 1000000000 # too big : error
Error: sch_sfq: invalid perturb period.

tc qd add dev lo root sfq perturb 2000000 # acceptable value
tc -s -d qd sh dev lo
qdisc sfq 8005: root refcnt 2 limit 127p quantum 64Kb depth 127 flows 128 divisor 1024 perturb 2000000sec
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0

Weakness: CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2025-38193?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-38193?

Apply the vendor's patch.

## Is CVE-2025-38193 being exploited?

There is no known exploitation of CVE-2025-38193 in the wild and no public exploit code.

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## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-38193 and fix it if it is affected.

What it is: CVE-2025-38193 is a high-severity vulnerability in Debian Debian Linux, published on 4 Jul 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-2025-38193 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-2025-38193/ (Markdown: https://insights.sbomify.com/CVE-2025-38193/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-38193
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-38193
- OSV: https://osv.dev/vulnerability/CVE-2025-38193

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-38193/
Summaries are generated and may contain mistakes; the official description above is the record.