# CVE-2024-56759: btrfs: fix use-after-free when COWing tree bock and tracing is enabled

> A use-after-free in the Linux kernel btrfs filesystem allows attackers to cause denial of service or execute code when tracing 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:** 6 Jan 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2024-56759, DEBIAN-CVE-2024-56759, GHSA-6574-vqv8-9334, UBUNTU-CVE-2024-56759

## What is CVE-2024-56759?

CVE-2024-56759 is a high-severity use after free vulnerability in Linux kernel, published on 6 Jan 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: fix use-after-free when COWing tree bock and tracing is enabled

When a COWing a tree block, at btrfs_cow_block(), and we have the
tracepoint trace_btrfs_cow_block() enabled and preemption is also enabled
(CONFIG_PREEMPT=y), we can trigger a use-after-free in the COWed extent
buffer while inside the tracepoint code. This is because in some paths
that call btrfs_cow_block(), such as btrfs_search_slot(), we are holding
the last reference on the extent buffer @buf so btrfs_force_cow_block()
drops the last reference on the @buf extent buffer when it calls
free_extent_buffer_stale(buf), which schedules the release of the extent
buffer with RCU. This means that if we are on a kernel with preemption,
the current task may be preempted before calling trace_btrfs_cow_block()
and the extent buffer already released by the time trace_btrfs_cow_block()
is called, resulting in a use-after-free.

Fix this by moving the trace_btrfs_cow_block() from btrfs_cow_block() to
btrfs_force_cow_block() before the COWed extent buffer is freed.
This also has a side effect of invoking the tracepoint in the tree defrag
code, at defrag.c:btrfs_realloc_node(), since btrfs_force_cow_block() is
called there, but this is fine and it was actually missing there.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2024-56759?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2024-56759?

Apply the vendor's patch.

## Is CVE-2024-56759 being exploited?

There is no known exploitation of CVE-2024-56759 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-2024-56759 and fix it if it is affected.

What it is: CVE-2024-56759 is a high-severity use after free vulnerability in Linux kernel, published on 6 Jan 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-2024-56759 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-2024-56759/ (Markdown: https://insights.sbomify.com/CVE-2024-56759/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-56759
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-56759
- OSV: https://osv.dev/vulnerability/CVE-2024-56759

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-56759/
Summaries are generated and may contain mistakes; the official description above is the record.