# CVE-2025-71067: ntfs: set dummy blocksize to read boot_block when mounting

> A local attacker can cause a denial of service in the Linux kernel by mounting a crafted NTFS filesystem with a large block size, triggering a null dereference.

- **Severity:** Not scored
- **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:** 13 Jan 2026
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-71067, DEBIAN-CVE-2025-71067, GHSA-wq7w-gfpq-89g4, ROOT-OS-DEBIAN-12-CVE-2025-71067, ROOT-OS-DEBIAN-13-CVE-2025-71067, ROOT-OS-UBUNTU-2204-CVE-2025-71067, ROOT-OS-UBUNTU-2404-CVE-2025-71067, UBUNTU-CVE-2025-71067

## What is CVE-2025-71067?

CVE-2025-71067 is a vulnerability in Linux, published on 13 Jan 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:

ntfs: set dummy blocksize to read boot_block when mounting

When mounting, sb->s_blocksize is used to read the boot_block without
being defined or validated. Set a dummy blocksize before attempting to
read the boot_block.

The issue can be triggered with the following syz reproducer:

  mkdirat(0xffffffffffffff9c, &(0x7f0000000080)='./file1\x00', 0x0)
  r4 = openat$nullb(0xffffffffffffff9c, &(0x7f0000000040), 0x121403, 0x0)
  ioctl$FS_IOC_SETFLAGS(r4, 0x40081271, &(0x7f0000000980)=0x4000)
  mount(&(0x7f0000000140)=@nullb, &(0x7f0000000040)='./cgroup\x00',
        &(0x7f0000000000)='ntfs3\x00', 0x2208004, 0x0)
  syz_clone(0x88200200, 0x0, 0x0, 0x0, 0x0, 0x0)

Here, the ioctl sets the bdev block size to 16384. During mount,
get_tree_bdev_flags() calls sb_set_blocksize(sb, block_size(bdev)),
but since block_size(bdev) > PAGE_SIZE, sb_set_blocksize() leaves
sb->s_blocksize at zero.

Later, ntfs_init_from_boot() attempts to read the boot_block while
sb->s_blocksize is still zero, which triggers the bug.

[almaz.alexandrovich@paragon-software.com: changed comment style, added
return value handling]

## Which versions are affected by CVE-2025-71067?


## How do I fix CVE-2025-71067?

Apply the vendor's patch.

## Is CVE-2025-71067 being exploited?

There is no known exploitation of CVE-2025-71067 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-71067 and fix it if it is affected.

What it is: CVE-2025-71067 is a vulnerability in Linux, published on 13 Jan 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-2025-71067 in the wild and no public exploit code.

Affected product: 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-2025-71067/ (Markdown: https://insights.sbomify.com/CVE-2025-71067/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-71067
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-71067
- OSV: https://osv.dev/vulnerability/CVE-2025-71067

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-71067/
Summaries are generated and may contain mistakes; the official description above is the record.