smb/client: fix chown/chgrp with SMB3 POSIX Extensions (CVE-2026-64388) | HOL Guard CVE

High · CVSS 7.8CVE-2026-64388

smb/client: fix chown/chgrp with SMB3 POSIX Extensions

Answer in brief

CVE-2026-64388 records a High severity (CVSS 7.8) vulnerability in smb/client: fix chown/chgrp with SMB3 POSIX Extensions. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Jul 25, 2026Updated Sep 4, 2026Source checked Sep 21, 2026First seen by HOL Aug 5, 2026Material review Sep 4, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 7.8
Exploitation: Not marked as known exploited
Affected software: 3 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 7.8. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Affected products and reported versions
Product	Affected versions	Fixed versions
cpe:2.3:o:linux:linux_kernel::::::::	Not reported	Not reported

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Linux/Linuxgeneric	>=b326614ea2159ea5c835d320f261d05d080cd201 <550cfb8a81181331d4d0f76ab75ee58a0bf41e3e \|\| >=b326614ea2159ea5c835d320f261d05d080cd201 <760ef2c579c2609cf17fb1cd5392f64d42d43d33	550cfb8a81181331d4d0f76ab75ee58a0bf41e3e, 760ef2c579c2609cf17fb1cd5392f64d42d43d33
Linux/Linuxgeneric	4.18	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Linux/Linux, Linux/Linux.
Review the reported fix. Update Linux/Linux to 550cfb8a81181331d4d0f76ab75ee58a0bf41e3e if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Jul 25, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 4, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 5, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.