# CVE-2025-40125: blk-mq: check kobject state_in_sysfs before deleting in blk_mq_unregister_hctx

> A local attacker with high privileges can trigger a kernel warning and potential denial of service by manipulating block device queue settings after a sysfs registration failure.

- **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:** 12 Nov 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-40125, DEBIAN-CVE-2025-40125, GHSA-8mqf-xr44-qqq9, ROOT-OS-UBUNTU-2404-CVE-2025-40125, UBUNTU-CVE-2025-40125

## What is CVE-2025-40125?

CVE-2025-40125 is a vulnerability in Linux, published on 12 Nov 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:

blk-mq: check kobject state_in_sysfs before deleting in blk_mq_unregister_hctx

In __blk_mq_update_nr_hw_queues() the return value of
blk_mq_sysfs_register_hctxs() is not checked. If sysfs creation for hctx
fails, later changing the number of hw_queues or removing disk will
trigger the following warning:

  kernfs: can not remove 'nr_tags', no directory
  WARNING: CPU: 2 PID: 637 at fs/kernfs/dir.c:1707 kernfs_remove_by_name_ns+0x13f/0x160
  Call Trace:
   remove_files.isra.1+0x38/0xb0
   sysfs_remove_group+0x4d/0x100
   sysfs_remove_groups+0x31/0x60
   __kobject_del+0x23/0xf0
   kobject_del+0x17/0x40
   blk_mq_unregister_hctx+0x5d/0x80
   blk_mq_sysfs_unregister_hctxs+0x94/0xd0
   blk_mq_update_nr_hw_queues+0x124/0x760
   nullb_update_nr_hw_queues+0x71/0xf0 [null_blk]
   nullb_device_submit_queues_store+0x92/0x120 [null_blk]

kobjct_del() was called unconditionally even if sysfs creation failed.
Fix it by checkig the kobject creation statusbefore deleting it.

## Which versions are affected by CVE-2025-40125?


## How do I fix CVE-2025-40125?

Apply the vendor's patch.

## Is CVE-2025-40125 being exploited?

There is no known exploitation of CVE-2025-40125 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40125 and fix it if it is affected.

What it is: CVE-2025-40125 is a vulnerability in Linux, published on 12 Nov 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-2025-40125 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-2025-40125/ (Markdown: https://insights.sbomify.com/CVE-2025-40125/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40125
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40125
- OSV: https://osv.dev/vulnerability/CVE-2025-40125

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40125/
Summaries are generated and may contain mistakes; the official description above is the record.