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

CVE-2026-99171 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-99171, released November 3, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-99171
- Priority: Routine
- CVSS: 4.7 (Moderate)
- EPSS: 0.0017
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 28, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-99171

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-99171](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99171.md) | Nov 3, 2026 |
| Linux | linux Debian 14 | 7.2.13-1 | [DEBIAN-CVE-2026-99171](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99171.md) | Nov 3, 2026 |

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Data as of 2026-11-08T19:12:23Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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