# CVE-2026-99171: ntfs3: free the sbi after a grace period


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 28 Oct 2026
- **Updated:** 28 Oct 2026
- **Also known as:** AZL-111320, BELL-CVE-2026-99171, DEBIAN-CVE-2026-99171, GHSA-2rj4-34vw-q254, UBUNTU-CVE-2026-99171

## What is CVE-2026-99171?

CVE-2026-99171 is a vulnerability in Linux, published on 28 Oct 2026. 

### Official description

In the Linux kernel, the following vulnerability has been resolved:

ntfs3: free the sbi after a grace period

If the "nocase" mount option ntfs3 uses custom hash and dentry compare
functions. Both access ntfs3 superblock private information in rcu
pathwalk. ntfs_put_super() and ntfs3_kill_sb() drop the info without any
rcu delay. A lookup that's still inside the filesystem when the last
reference to the mount is dropped causes a UAF. With a pathwalk held up
in ntfs_d_hash() while the last reference to the mount goes away:

  BUG: KASAN: slab-use-after-free in ntfs_nls_to_utf16+0x752/0x940
  Read of size 8 at addr ff1100010453c850 by task walker/99
  Call Trace:
   <TASK>
   ntfs_nls_to_utf16+0x752/0x940
   ntfs_d_hash+0x22b/0x500
   link_path_walk+0x11ad/0x1d30
   path_lookupat+0x63/0xb00
   filename_lookup+0x1f1/0x5b0
   vfs_statx+0xd7/0x3b0
  [...]
  Allocated by task 95:
   __kmalloc_cache_noprof+0x249/0x560
   ntfs_init_fs_context+0x2db/0x5a0
   alloc_fs_context+0x52e/0xc70
  [...]
  Freed by task 98:
   kfree+0x1db/0x5b0
   deactivate_locked_super+0x9c/0xf0
   cleanup_mnt+0x9f/0x130
   task_work_run+0x131/0x250

The bug is currently masked by the grace period in namespace_unlock()
for umount(2). Keep the necessary information until the filesystem
private info is freed and free it with an rcu delay.

ntfs3_free_sbi() now runs from an rcu callback and drops the upcase
table via ntfs_put_shared(). So switch s_shared_lock over to
spin_lock_bh(). Otherwise the callback can deadlock against a task
holding the lock on the same cpu.

## Which versions are affected by CVE-2026-99171?


## How do I fix CVE-2026-99171?

Upgrade to a fixed version.

## Is CVE-2026-99171 being exploited?

There is no known exploitation of CVE-2026-99171 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99171 and fix it if it is affected.

What it is: CVE-2026-99171 is a vulnerability in Linux, published on 28 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99171 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-2026-99171/ (Markdown: https://insights.sbomify.com/CVE-2026-99171/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99171
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99171
- OSV: https://osv.dev/vulnerability/CVE-2026-99171

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99171/
Summaries are generated and may contain mistakes; the official description above is the record.