CVE-2026-64388

highCVSS 7.8covered by 2 sourcesfirst seen 2026-07-25

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.

CSIRTS triage

Other

What: The chown/chgrp operations with SMB3 POSIX Extensions are fixed.
Who is affected: Deployments using SMB client with POSIX Extensions.
Urgency: Remediation is necessary to maintain proper file permissions, with no known exploits.
Action: Apply the patch when it becomes available.

AI-assisted analysis generated from the source advisory — verify against the original.

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Exploitation outlook

Low exploitation risk0.12% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 2% of all EPSS-scored CVEs.

Advisory coverage (2)

mediumCVE-2026-64388: smb/client: fix chown/chgrp with SMB3 POSIX Extensionsmsrc · 2026-08-06
highCVE-2026-64388: In the Linux kernel, the following vulnerability has been resolved: smb/client: fix chown/chgr…nvd · 2026-07-25

External references

NVD record for CVE-2026-64388

CVE.org record

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