CVE-2026-89785 fs/ntfs3: fix out-of-bounds read of INDEX_ROOT in reparse/objid init
A local attacker with CAP_SYS_ADMIN can trigger an out-of-bounds read in the Linux kernel NTFS3 driver by mounting a crafted image, potentially causing a crash or leaking memory.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89785?
CVE-2026-89785 is a memory corruption vulnerability in Linux, published on 16 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
fs/ntfs3: fix out-of-bounds read of INDEX_ROOT in reparse/objid init
ntfs_reparse_init() and ntfs_objid_init() parse the index root of the $Extend/$Reparse and $Extend/$ObjId metafiles (the INDEX_ROOT attributes named $R and $O). They read its type and rule fields through resident_data(), which does not check that the resident attribute is large enough to hold them.
mi_enum_attr() accepts a resident attribute with data_off == asize and data_size == 0. For such an attribute placed last in its MFT record, resident_data() returns a pointer to the end of the record_size buffer, so reading root->type / root->rule reads past the allocation.
Use resident_data_ex(attr, sizeof(struct INDEX_ROOT)) and bail out when it returns NULL, as ntfs_security_init() already does for $SDH / $SII.
The attribute is only parsed while mounting a crafted image, so this needs CAP_SYS_ADMIN.
BUG: KASAN: slab-out-of-bounds in ntfs_reparse_init (fs/ntfs3/fsntfs.c:2306) Read of size 4 at addr ffff88801219dc00 by task mount ntfs_reparse_init (fs/ntfs3/fsntfs.c:2306) ntfs_fill_super (fs/ntfs3/super.c:1604) get_tree_bdev_flags (fs/super.c:1703) vfs_get_tree (fs/super.c:1758) path_mount (fs/namespace.c:4131) __x64_sys_mount (fs/namespace.c:4360)
Which versions are affected by CVE-2026-89785?
How do I fix CVE-2026-89785?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-89785 being exploited?
There is no known exploitation of CVE-2026-89785 in the wild and no public exploit code.
Sources
Also known as AZL-101345, BELL-CVE-2026-89785, DEBIAN-CVE-2026-89785, GHSA-683x-gqv7-78pp, UBUNTU-CVE-2026-89785.