Bug 2507062 (CVE-2026-64388)

Summary:	CVE-2026-64388 kernel: smb/client: fix chown/chgrp with SMB3 POSIX Extensions
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	low	Docs Contact:
Priority:	low
Version:	unspecified	CC:	rhel-process-autobot, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in the Linux kernel's Server Message Block (SMB) client. When mounting filesystems using SMB3 POSIX Extensions, modifications to file ownership (chown) and group (chgrp) were not correctly applied on the server unless specific mount options were also enabled. This could allow a local user to set incorrect file permissions, potentially leading to unauthorized access to sensitive information or unintended privilege escalation.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-07-25 10:03:01 UTC

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.

Comment 1 Mauro Matteo Cascella 2026-07-29 22:25:04 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026072527-CVE-2026-64388-82d9@gregkh/T