# CVE-2025-39759: btrfs: qgroup: fix race between quota disable and quota rescan ioctl

> A race condition in the Linux kernel btrfs filesystem allows local attackers to trigger a use-after-free, potentially leading to code execution or privilege escalation.

- **Severity:** High 7.0 (`CVSS:3.1/AV:L/AC:H/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:** 11 Sep 2025
- **Updated:** 12 May 2026
- **Also known as:** AZL-67205, AZL-73959, BELL-CVE-2025-39759, DEBIAN-CVE-2025-39759, GHSA-f7p4-h976-ch7q, ROOT-OS-DEBIAN-11-CVE-2025-39759, ROOT-OS-UBUNTU-2204-CVE-2025-39759, ROOT-OS-UBUNTU-2404-CVE-2025-39759, UBUNTU-CVE-2025-39759

## What is CVE-2025-39759?

CVE-2025-39759 is a high-severity use after free vulnerability in Debian Debian Linux, published on 11 Sep 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:

btrfs: qgroup: fix race between quota disable and quota rescan ioctl

There's a race between a task disabling quotas and another running the
rescan ioctl that can result in a use-after-free of qgroup records from
the fs_info->qgroup_tree rbtree.

This happens as follows:

1) Task A enters btrfs_ioctl_quota_rescan() -> btrfs_qgroup_rescan();

2) Task B enters btrfs_quota_disable() and calls
   btrfs_qgroup_wait_for_completion(), which does nothing because at that
   point fs_info->qgroup_rescan_running is false (it wasn't set yet by
   task A);

3) Task B calls btrfs_free_qgroup_config() which starts freeing qgroups
   from fs_info->qgroup_tree without taking the lock fs_info->qgroup_lock;

4) Task A enters qgroup_rescan_zero_tracking() which starts iterating
   the fs_info->qgroup_tree tree while holding fs_info->qgroup_lock,
   but task B is freeing qgroup records from that tree without holding
   the lock, resulting in a use-after-free.

Fix this by taking fs_info->qgroup_lock at btrfs_free_qgroup_config().
Also at btrfs_qgroup_rescan() don't start the rescan worker if quotas
were already disabled.

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2025-39759?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-39759?

Apply the vendor's patch.

## Is CVE-2025-39759 being exploited?

There is no known exploitation of CVE-2025-39759 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-2025-39759 and fix it if it is affected.

What it is: CVE-2025-39759 is a high-severity use after free vulnerability in Debian Debian Linux, published on 11 Sep 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-2025-39759 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-2025-39759/ (Markdown: https://insights.sbomify.com/CVE-2025-39759/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-39759
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-39759
- OSV: https://osv.dev/vulnerability/CVE-2025-39759

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-39759/
Summaries are generated and may contain mistakes; the official description above is the record.