CVE-2026-64398

Technical Description

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

ksmbd: add a permission check for FSCTL_SET_ZERO_DATA

FSCTL_SET_ZERO_DATA in smb2_ioctl() destroys file data via

ksmbd_vfs_zero_data() -> vfs_fallocate(PUNCH_HOLE/ZERO_RANGE) after

checking only the share-level KSMBD_TREE_CONN_FLAG_WRITABLE, with no

per-handle access check. A handle opened with only FILE_WRITE_ATTRIBUTES

still yields an FMODE_WRITE filp (FILE_WRITE_ATTRIBUTES is part of

FILE_WRITE_DESIRE_ACCESS_LE, so smb2_create_open_flags() opens it

O_WRONLY), so the vfs_fallocate FMODE_WRITE check does not stop it; only

the missing fp->daccess gate would. Reproduced on mainline 7.1-rc7 with

KASAN by an authenticated SMB client: a FILE_WRITE_ATTRIBUTES-only handle

zeroed 4096 bytes of file data it had no FILE_WRITE_DATA right to

(6/6; a FILE_READ_DATA-only handle was correctly denied).

This is the unfixed sibling of commit cc57232cae23 ("ksmbd: fix FSCTL

permission bypass by adding a permission check for FSCTL_SET

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References