CVE-2026-63833: ntfs3: reject direct userspace writes to reserved $LX* xattrs

CVE-2026-63833: ntfs3: reject direct userspace writes to reserved $LX* xattrs

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

ntfs3: reject direct userspace writes to reserved $LX* xattrs

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]

The Linux kernel CVE team has assigned CVE-2026-63833 to this issue.


Affected and fixed versions
===========================

	Fixed in 5.15.211 with commit e574af95234afc3c725988bbc1fdeb46b9f386a4
	Fixed in 6.1.177 with commit 2c3cd6da4a14380ef79e34bd9dff7caf46687477
	Fixed in 6.6.144 with commit e8852ae29868e449fdb47eebc28f35fb80741a5f
	Fixed in 6.12.95 with commit f8d420949b335a4b51d06ab276beee6b8dfdc909
	Fixed in 6.18.38 with commit 5e658b9245a52d838ef93729a7bc07de8e19deb7
	Fixed in 7.1.3 with commit 293a84fa40b3a1b3471c0545722724bc10973f76
	Fixed in 7.2-rc1 with commit 5b08dccecf825cbf905f348bc6ccb497507e28e2

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-63833
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/ntfs3/xattr.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/e574af95234afc3c725988bbc1fdeb46b9f386a4
	https://git.kernel.org/stable/c/2c3cd6da4a14380ef79e34bd9dff7caf46687477
	https://git.kernel.org/stable/c/e8852ae29868e449fdb47eebc28f35fb80741a5f
	https://git.kernel.org/stable/c/f8d420949b335a4b51d06ab276beee6b8dfdc909
	https://git.kernel.org/stable/c/5e658b9245a52d838ef93729a7bc07de8e19deb7
	https://git.kernel.org/stable/c/293a84fa40b3a1b3471c0545722724bc10973f76
	https://git.kernel.org/stable/c/5b08dccecf825cbf905f348bc6ccb497507e28e2