CVE-2026-64388 smb/client: fix chown/chgrp with SMB3 POSIX Extensions
The Linux kernel SMB client fails to apply ownership changes when using SMB3 POSIX extensions without specific mount options, leading to incorrect file permissions.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-64388?
CVE-2026-64388 is a high-severity vulnerability in Linux kernel, published on 25 Jul 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:
smb/client: fix chown/chgrp with SMB3 POSIX Extensions
Ownership (chown) and group (chgrp) modifications were being ignored when mounting with SMB3 POSIX Extensions unless CIFS_MOUNT_CIFS_ACL or CIFS_MOUNT_MODE_FROM_SID were also explicitly set.
Fix this by checking for posix_extensions in cifs_setattr_nounix() when updating UID and GID, ensuring that id_mode_to_cifs_acl() is called to map and set the ownership/group information on the server.
Weakness: CWE-682
Which versions are affected by CVE-2026-64388?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-64388?
Apply the vendor's patch.
Is CVE-2026-64388 being exploited?
There is no known exploitation of CVE-2026-64388 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-93753, BELL-CVE-2026-64388, DEBIAN-CVE-2026-64388, GHSA-p59x-f8qp-h8m2, ROOT-OS-DEBIAN-12-CVE-2026-64388, ROOT-OS-DEBIAN-13-CVE-2026-64388 and 2 more.