# CVE-2026-64239: mm/damon/sysfs-schemes: delete tried region in regions_rmdirs()

> A use-after-free in the Linux kernel DAMON sysfs interface allows local attackers to potentially execute code or escalate privileges when debug kobject release is enabled.

- **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:** 24 Jul 2026
- **Updated:** 24 Jul 2026
- **Also known as:** BELL-CVE-2026-64239, DEBIAN-CVE-2026-64239, GHSA-v8wj-8j36-23j2, ROOT-OS-UBUNTU-2204-CVE-2026-64239, UBUNTU-CVE-2026-64239

## What is CVE-2026-64239?

CVE-2026-64239 is a high-severity use after free vulnerability in Linux kernel, published on 24 Jul 2026. 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/sysfs-schemes: delete tried region in regions_rmdirs()

DAMON sysfs maintains the DAMOS tried region directory objects via a
linked list.  When the user requests refresh of the directories, DAMON
sysfs removes all the region directories first, and then generate updated
regions directory on the empty space.  The removal function
(damon_sysfs_scheme_regions_rm_dirs()) only puts the kobj objects. 
Deletion of the container region object from the linked list is done
inside the kobj release callback function.

If somehow the callback invocation is delayed, the list will contain
regions list that gonna be freed.  If the updated region directories
creation is started in this situation, the list can be corrupted and
use-after-free can happen.

Because the kobj objects are managed by only DAMON sysfs, the issue cannot
happen in normal situation.  But, such delays can be made on kernels that
built with CONFIG_DEBUG_KOBJECT_RELEASE.  On the kernel, the issue can
indeed be reproduced like below.

    # damo start --damos_action stat
    # cd /sys/kernel/mm/damon/admin/kdamonds/0/
    # for i in {1..10}; do echo update_schemes_tried_regions > state; done
    # dmesg | grep underflow
    [   89.296152] refcount_t: underflow; use-after-free.

Fix the issue by removing the region object from the list when
decrementing the reference count.

Also update damos_sysfs_populate_region_dir() to add the region object to
the list only after the kobject_init_and_add() is success, so that fail of
kobject_init_and_add() is not leaving the deallocated object on the list.

The issue was discovered [1] by Sashiko.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-64239?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-64239?

Apply the vendor's patch.

## Is CVE-2026-64239 being exploited?

There is no known exploitation of CVE-2026-64239 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64239 and fix it if it is affected.

What it is: CVE-2026-64239 is a high-severity use after free vulnerability in Linux kernel, published on 24 Jul 2026. 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-2026-64239 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-64239/ (Markdown: https://insights.sbomify.com/CVE-2026-64239/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64239
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64239
- OSV: https://osv.dev/vulnerability/CVE-2026-64239

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64239/
Summaries are generated and may contain mistakes; the official description above is the record.