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CVE-2026-72186
ntfs: make system files immutable to prevent corruption
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem fs/ntfs. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-72186 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
When a system file such as $Bitmap is exposed via show_sys_files and written from userspace, the volume is corrupted and, because the cluster allocator scans $Bitmap through the same inode's page cache, a write to $Bitmap also deadlocks writeback against the folio it already holds locked. These files are maintained by the driver itself and have no valid reason to be written through the file interface. Mark base metadata files (mft_no < FILE_first_user) as immutable during inode read so the VFS rejects write, mmap, truncate and unlink with -EPERM. Directories are skipped so the root and $Extend remain usable. Internal metadata updates do not go through the VFS write path and are unaffected.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
fs/ntfs/inode.c
- What this is
- NTFS FILESYSTEMMAINTAINERS section matched on fs/ntfs/ · linux-fsdevel@vger.kernel.org · Maintained
- Kernel module
- ntfs
Check it on the machine
grep -w CONFIG_NTFS_FS /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w ntfsPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian does not build this code in 1 release. It does build it in 2 releases, so the answer depends on which release the machine runs. The build rule could not be established for 1 release, so nothing is claimed about those.
- bookwormn
- trixie?
- forky, sidm
- n
- not enabled on any flavour - this release does not build the code
- ?
- not established - no Makefile entry for the affected file
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switch
- CONFIG_NTFS_FS
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-08-15 (2 months ago)source
- CVSS
- 9.1 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.50%, higher than 41.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- fs/ntfs
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 7.1 | 7.1.5 | 8f313e92522a |
| 7.1 | 7.2 | f72df3a4c33b |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- fs/ntfs registers ntfs_export_ops; remote nfsd/ksmbd write RPCs reach ntfs_file_write_iter on $Bitmap, and dual-boot/shared NTFS volumes are commonly rw-mounted and network-exported on NAS/hybrid servers.
- AC:LAttack complexity, low
- Without S_IMMUTABLE, opening $Bitmap by name and writing is deterministic; expanding $Bitmap triggers ntfs_attr_map_cluster while lcnalloc holds the same folio locked, deadlocking writeback as documented in the fix commit.
- PR:NPrivileges required, none
- Exploitation needs only permission to write on a mounted NTFS volume (default i_mode 0777 with fmask=0, uid/gid mount options, authenticated SMB/NFS client, or guest write); no CAP_SYS_ADMIN or init-namespace root is required at trigger time.
- UI:NUser interaction, none
- Once an administrator has rw-mounted and optionally exported the NTFS volume, the attacker issues normal write/mmap/truncate/unlink to $Bitmap or other mft_no<FILE_first_user files; no per-attack victim interaction is required.
- S:UScope, unchanged
- Impact is on-disk NTFS metadata corruption and kernel thread deadlock within the host filesystem/kernel authority; this is standard filesystem abuse, not a VM escape, container breakout, or IOMMU boundary bypass.
- C:NConfidentiality impact, none
- The flaw is attacker-initiated writes to exposed system files and resulting metadata corruption; it does not perform kernel out-of-bounds reads, use-after-free, or other memory-disclosure primitives.
- I:HIntegrity impact, high
- Writing $Bitmap (or $MFT, $LogFile, $Boot, etc.) lets an attacker directly control cluster-allocation state, causing arbitrary on-disk metadata corruption and steered overwrites of live file data clusters across the volume.
- A:HAvailability impact, high
- Concurrent $Bitmap writes deadlock the cluster allocator against writeback on the same folio, hanging kernel I/O threads, and corrupted allocation bitmaps can render the NTFS volume inconsistent and unusable on remount.