# CVE-2025-37797: net_sched: hfsc: Fix a UAF vulnerability in class handling

> A use-after-free flaw in the Linux kernel's HFSC qdisc allows local attackers to potentially execute code or escalate privileges via race conditions.

- **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:** 2 May 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-37797, DEBIAN-CVE-2025-37797, GHSA-hvr4-ppmm-c7fp, ROOT-OS-DEBIAN-12-CVE-2025-37797, ROOT-OS-UBUNTU-2204-CVE-2025-37797, ROOT-OS-UBUNTU-2404-CVE-2025-37797, SUSE-SU-2025:02671-1, SUSE-SU-2025:02707-1, UBUNTU-CVE-2025-37797

## What is CVE-2025-37797?

CVE-2025-37797 is a high-severity use after free vulnerability in Debian Debian Linux, published on 2 May 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: hfsc: Fix a UAF vulnerability in class handling

This patch fixes a Use-After-Free vulnerability in the HFSC qdisc class
handling. The issue occurs due to a time-of-check/time-of-use condition
in hfsc_change_class() when working with certain child qdiscs like netem
or codel.

The vulnerability works as follows:
1. hfsc_change_class() checks if a class has packets (q.qlen != 0)
2. It then calls qdisc_peek_len(), which for certain qdiscs (e.g.,
   codel, netem) might drop packets and empty the queue
3. The code continues assuming the queue is still non-empty, adding
   the class to vttree
4. This breaks HFSC scheduler assumptions that only non-empty classes
   are in vttree
5. Later, when the class is destroyed, this can lead to a Use-After-Free

The fix adds a second queue length check after qdisc_peek_len() to verify
the queue wasn't emptied.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2025-37797?

It affects 2 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `kernel-livepatch-SLE15-SP3_Update_59` | SUSE:Linux Enterprise Live Patching 15 SP3 | All versions | 2-150300.2.1 |
| `kernel-livepatch-SLE15-SP5_Update_28` | SUSE:Linux Enterprise Live Patching 15 SP5 | All versions | 2-150500.2.1 |

Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-37797?

Apply the vendor's patch.

## Is CVE-2025-37797 being exploited?

There is no known exploitation of CVE-2025-37797 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-2025-37797 and fix it if it is affected.

What it is: CVE-2025-37797 is a high-severity use after free vulnerability in Debian Debian Linux, published on 2 May 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-2025-37797 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-2025-37797/ (Markdown: https://insights.sbomify.com/CVE-2025-37797/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-37797
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-37797
- OSV: https://osv.dev/vulnerability/CVE-2025-37797

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-37797/
Summaries are generated and may contain mistakes; the official description above is the record.