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CVE-2026-72211
ntfs: grow index root value before reparent header update
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-2026-72211 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
ntfs_ir_reparent() moves the resident index root entries into an index block and leaves a small root stub containing the child VCN. That root stub can be larger than the existing resident value. For example, an empty root with value_length 48 has an index area of 32 bytes, while the large-index root stub needs index_length and allocated_size of 40 bytes. The current code publishes the larger index.index_length and index.allocated_size before resizing the resident value. If the resize returns -ENOSPC, the recovery path can call ntfs_inode_add_attrlist(), which looks attributes up again while the root header says allocated_size 40 but the resident value still only provides 32 bytes of index area. Lookup-time $INDEX_ROOT validation then correctly rejects that transient layout as corrupt. This reproduces as a generic/013 failure under qemu. In the failing run, the transient root had value_len=48, index_size=32, index_length=40, and allocated_size=40, and ntfsprogs-plus ntfsck reported "Corrupt index root in MFT record 1177". When the root stub grows, resize the resident value before publishing the larger root header. If the resize fails, the old root remains valid for recovery lookups. Keep the existing header-before-resize ordering for shrink or same-size cases so the resident value never temporarily exposes an allocated_size beyond its bounds.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
fs/ntfs/index.c
- What this is
- NTFS FILESYSTEMMAINTAINERS section matched on fs/ntfs/ · linux-fsdevel@vger.kernel.org · Maintained
- Kernel module
- ntfs
Check it on the machine
grep -w CONFIG_NTFS_FS /boot/config-$(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
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.55%, higher than 45.0% 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 | 38d444271604 |
| 7.1 | 7.2 | 0bb508fb3b97 |
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
- ntfs_ir_reparent is reached via ntfs_index_add_filename on VFS create/mkdir/link/rename; the ntfs driver registers ntfs_export_ops, so remote NFS or ksmbd clients writing to an exported rw NTFS share can trigger index reparent without local shell access.
- AC:LAttack complexity, low
- An attacker can deterministically fill a directory and pack the host MFT record so index-root reparent needs a larger stub than the resident value_length, forcing -ENOSPC on resize; xfstests generic/013 reproduces this without races or victim-specific timing.
- PR:NPrivileges required, none
- Exploitation requires only permission to create or link files in an NTFS directory (local user with write access, authenticated SMB/NFS client, or guest/anonymous write on a misconfigured export); mounting is environmental setup, not a privilege needed during the trigger.
- UI:NUser interaction, none
- Once an administrator has rw-mounted and optionally exported the NTFS volume, the attacker drives file-creation or link operations that grow the directory index; no further victim clicks, opens, or cooperative actions are required beyond that standing configuration.
- S:UScope, unchanged
- Impact is confined to on-disk NTFS $INDEX_ROOT metadata corruption and operation failure within the host kernel/filesystem security authority; this is standard local or network filesystem exploitation, not a VM escape or cross-authority sandbox breakout.
- C:HConfidentiality impact, high
- Publishing allocated_size beyond the resident value index area leaves a transient header/buffer mismatch in the mapped MFT record; recovery lookups and subsequent index walks can read past the resident value bounds, and persistent corrupt $INDEX_ROOT can expose adjacent directory/MFT metadata.
- I:HIntegrity impact, high
- Failed reparent can leave $INDEX_ROOT with index_length and allocated_size larger than the resident value (ntfsck reports Corrupt index root in MFT record), enabling attacker-steerable on-disk directory index metadata corruption beyond the intended filesystem state.
- A:HAvailability impact, high
- Recovery fails when $INDEX_ROOT validation rejects the inconsistent root, aborting directory updates and leaving corrupt on-disk index metadata that can render directories unusable; this was reproduced as an xfstests generic/013 failure with persistent filesystem corruption.