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CVE-2026-63833
ntfs3: reject direct userspace writes to reserved $LX* xattrs
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem fs/ntfs3. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-63833 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 | fixed | 6.1.177-1 | Update the kernel and reboot. Fixed in 6.1.177-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.95-1 | Update the kernel and reboot. Fixed in 6.12.95-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.3-1 | Update the kernel and reboot. Fixed in 7.1.3-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.3-1 | Update the kernel and reboot. Fixed in 7.1.3-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
NTFS3 uses $LXUID, $LXGID, $LXMOD and $LXDEV as internal WSL permission metadata and reloads them into i_uid, i_gid and i_mode from ntfs_get_wsl_perm(). Because the empty-prefix xattr handler also lets file owners call setxattr() on these names directly, an unprivileged writer on a writable ntfs3 mount can plant root ownership and S_ISUID on their own file and gain euid 0 after inode reload. Reject direct userspace writes to the reserved $LX* names. Internal ntfs3 metadata updates are unchanged because ntfs_save_wsl_perm() writes them via ntfs_set_ea() directly. [almaz.alexandrovich@paragon-software.com: added an additional check for non privileged users]
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
fs/ntfs3/xattr.c
- What this is
- NTFS3 FILESYSTEMMAINTAINERS section matched on fs/ntfs3/ · ntfs3@lists.linux.dev · Supported
- Kernel module
- ntfs3
Check it on the machine
grep -w CONFIG_NTFS3_FS /boot/config-$(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 ntfs3Prints 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 3 releases. It does build it in 1 release, so the answer depends on which release the machine runs.
- bookwormn
- trixiem
- forky, sidn
- n
- not enabled on any flavour - this release does not build the code
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switch
- CONFIG_NTFS3_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
- 2026-07-19 (3 months ago)source
- CVSS
- 7.1 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Nsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.12%, higher than 2.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- fs/ntfs3
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.15 | 5.15.211 | e574af95234a |
| 5.15 | 6.1.177 | 2c3cd6da4a14 |
| 5.15 | 6.6.144 | e8852ae29868 |
| 5.15 | 6.12.95 | f8d420949b33 |
| 5.15 | 6.18.38 | 5e658b9245a5 |
| 5.15 | 7.1.3 | 293a84fa40b3 |
| 5.15 | 7.2 | 5b08dccecf82 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4700-1 | 2026-07-26 | bullseye 6.1.177-1~deb11u1 | tracker |
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:LAttack vector, local
- Exploitation requires the setxattr/fsetxattr syscall against an ntfs3-mounted filesystem; ksmbd and nfsd prefix xattr names with "user." so they cannot reach the empty-prefix "$LX*" handler.
- AC:LAttack complexity, low
- An attacker reliably sets the three 4-byte xattrs on a file they own, then forces inode reload via dentry eviction under self-induced memory pressure or umount/remount in a user namespace.
- PR:LPrivileges required, low
- Any unprivileged local user with write access to their own file on a writable ntfs3 mount can trigger the bug; mounting ntfs3 in a user namespace only requires CAP_SYS_ADMIN within that namespace, which counts as Low.
- UI:NUser interaction, none
- No victim interaction is needed at exploit time; the attacker uses their own local account on an already-mounted writable ntfs3 volume (common on dual-boot/shared NTFS data partitions).
- S:UScope, unchanged
- Successful exploitation yields host root privileges within the same kernel security domain; it is standard local privilege escalation, not a cross-boundary escape.
- C:HConfidentiality impact, high
- Planting root ownership and S_ISUID on an executable and executing it after inode reload grants effective UID 0, providing full read access to all kernel-managed data on the system.
- I:HIntegrity impact, high
- The bug allows arbitrary tampering with kernel-trusted ownership and permission metadata, culminating in root code execution with unrestricted ability to modify any system data.
- A:NAvailability impact, none
- The vulnerability is a metadata permission bypass with no kernel crash, panic, hang, or denial-of-service component; availability is unaffected by the flaw itself.