# CVE-2025-39999: blk-mq: fix blk_mq_tags double free while nr_requests grown

> A local attacker with high privileges can trigger a double free in the Linux kernel block layer, causing a system crash.

- **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:** 15 Oct 2025
- **Updated:** 23 May 2026
- **Also known as:** BELL-CVE-2025-39999, DEBIAN-CVE-2025-39999, GHSA-28j8-2q92-jm59, UBUNTU-CVE-2025-39999

## What is CVE-2025-39999?

CVE-2025-39999 is an use after free vulnerability in Linux, published on 15 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:

blk-mq: fix blk_mq_tags double free while nr_requests grown

In the case user trigger tags grow by queue sysfs attribute nr_requests,
hctx->sched_tags will be freed directly and replaced with a new
allocated tags, see blk_mq_tag_update_depth().

The problem is that hctx->sched_tags is from elevator->et->tags, while
et->tags is still the freed tags, hence later elevator exit will try to
free the tags again, causing kernel panic.

Fix this problem by replacing et->tags with new allocated tags as well.

Noted there are still some long term problems that will require some
refactor to be fixed thoroughly[1].

[1] https://lore.kernel.org/all/20250815080216.410665-1-yukuai1@huaweicloud.com/

## Which versions are affected by CVE-2025-39999?


## How do I fix CVE-2025-39999?

Apply the vendor's patch.

## Is CVE-2025-39999 being exploited?

There is no known exploitation of CVE-2025-39999 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-39999 and fix it if it is affected.

What it is: CVE-2025-39999 is an use after free vulnerability in Linux, published on 15 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-2025-39999 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-2025-39999/ (Markdown: https://insights.sbomify.com/CVE-2025-39999/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-39999
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-39999
- OSV: https://osv.dev/vulnerability/CVE-2025-39999

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-39999/
Summaries are generated and may contain mistakes; the official description above is the record.