# CVE-2025-39909: mm/damon/lru_sort: avoid divide-by-zero in damon_lru_sort_apply_parameters()

> A divide-by-zero error in the Linux kernel's DAMON LRU_SORT module can cause a system crash if specific parameters are misconfigured.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 1 Oct 2025
- **Updated:** 11 May 2026
- **Also known as:** AZL-68013, BELL-CVE-2025-39909, DEBIAN-CVE-2025-39909, GHSA-jh5r-m3qc-3584, ROOT-OS-UBUNTU-2404-CVE-2025-39909, UBUNTU-CVE-2025-39909

## What is CVE-2025-39909?

CVE-2025-39909 is a medium-severity denial of service vulnerability in Debian Debian Linux, published on 1 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:

mm/damon/lru_sort: avoid divide-by-zero in damon_lru_sort_apply_parameters()

Patch series "mm/damon: avoid divide-by-zero in DAMON module's parameters
application".

DAMON's RECLAIM and LRU_SORT modules perform no validation on
user-configured parameters during application, which may lead to
division-by-zero errors.

Avoid the divide-by-zero by adding validation checks when DAMON modules
attempt to apply the parameters.

This patch (of 2):

During the calculation of 'hot_thres' and 'cold_thres', either
'sample_interval' or 'aggr_interval' is used as the divisor, which may
lead to division-by-zero errors.  Fix it by directly returning -EINVAL
when such a case occurs.  Additionally, since 'aggr_interval' is already
required to be set no smaller than 'sample_interval' in damon_set_attrs(),
only the case where 'sample_interval' is zero needs to be checked.

Weakness: CWE-369 (Divide By Zero)

## Which versions are affected by CVE-2025-39909?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-39909?

Apply the vendor's patch.

## Is CVE-2025-39909 being exploited?

There is no known exploitation of CVE-2025-39909 in the wild and no public exploit code.

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## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-39909 and fix it if it is affected.

What it is: CVE-2025-39909 is a medium-severity denial of service vulnerability in Debian Debian Linux, published on 1 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-2025-39909 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-2025-39909/ (Markdown: https://insights.sbomify.com/CVE-2025-39909/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-39909
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-39909
- OSV: https://osv.dev/vulnerability/CVE-2025-39909

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-39909/
Summaries are generated and may contain mistakes; the official description above is the record.