---
id: "CVE-2026-99171"
kind: "vulnerability"
aliases: ["CVE-2026-99171"]
title: "Linux kernel ntfs3: use-after-free in filename lookup after unmount"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "other"
products: []
ecosystems: []
tags: ["linux-kernel", "ntfs3", "other", "self-hosted"]
not_affected_if: ["default-config", "no-ntfs3-mounts"]
published_at: "2026-10-28T11:17:37+00:00"
first_seen_at: "2026-10-28T11:32:36+00:00"
updated_at: "2026-10-28T11:35:38+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99171", "first_seen_at": "2026-10-28T11:32:36+00:00"}]
---

# Linux kernel ntfs3: use-after-free in filename lookup after unmount

The ntfs3 driver in the Linux kernel frees its superblock private data too early when a mount with the nocase option is unmounted during an RCU path walk. A concurrent file lookup can then read freed memory, which can crash the kernel or be turned into further compromise.

_Summary, check and fix written by a model from the sources; labelled as such._

## Timeline

- 2026-10-28T11:32:36+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99171

## From the sources

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.

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