# CVE-2026-46159: btrfs: fix btrfs_ioctl_space_info() slot_count TOCTOU which can lead to info-leak

> A race condition in the Linux kernel btrfs filesystem allows local attackers to read uninitialized heap memory via an information leak.

- **Severity:** Medium 4.7 (`CVSS:3.1/AV:L/AC:H/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:** 28 May 2026
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-88815, BELL-CVE-2026-46159, DEBIAN-CVE-2026-46159, GHSA-8m37-fqxx-cfwj, ROOT-OS-DEBIAN-11-CVE-2026-46159, ROOT-OS-DEBIAN-12-CVE-2026-46159, ROOT-OS-UBUNTU-2204-CVE-2026-46159, ROOT-OS-UBUNTU-2404-CVE-2026-46159, UBUNTU-CVE-2026-46159

## What is CVE-2026-46159?

CVE-2026-46159 is a medium-severity vulnerability in Linux kernel, published on 28 May 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:

btrfs: fix btrfs_ioctl_space_info() slot_count TOCTOU which can lead to info-leak

btrfs_ioctl_space_info() has a TOCTOU race between two passes over the
block group RAID type lists. The first pass counts entries to determine
the allocation size, then the second pass fills the buffer. The
groups_sem rwlock is released between passes, allowing concurrent block
group removal to reduce the entry count.

When the second pass fills fewer entries than the first pass counted,
copy_to_user() copies the full alloc_size bytes including trailing
uninitialized kmalloc bytes to userspace.

Fix by copying only total_spaces entries (the actually-filled count from
the second pass) instead of alloc_size bytes, and switch to kzalloc so
any future copy size mismatch cannot leak heap data.

Weakness: CWE-367 (Time-of-check Time-of-use (TOCTOU) Race Condition)

## Which versions are affected by CVE-2026-46159?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-46159?

Apply the vendor's patch.

## Is CVE-2026-46159 being exploited?

There is no known exploitation of CVE-2026-46159 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-2026-46159 and fix it if it is affected.

What it is: CVE-2026-46159 is a medium-severity vulnerability in Linux kernel, published on 28 May 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-2026-46159 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-2026-46159/ (Markdown: https://insights.sbomify.com/CVE-2026-46159/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-46159
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-46159
- OSV: https://osv.dev/vulnerability/CVE-2026-46159

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-46159/
Summaries are generated and may contain mistakes; the official description above is the record.