CVE-2026-64388: smb/client: fix chown/chgrp with SMB3 POSIX Extensions

mediumCVSS 4.4CVE-2026-64388

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.

Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: medium — CVSS 4.4
Published: 2026-08-06
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-64388

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-643880.12% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 2% of all EPSS-scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-64388	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

highCVE-2026-64388: In the Linux kernel, the following vulnerability has been resolved: smb/client: fix chown/chgr…nvd

Recent advisories for smb/client

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

highCVE-2026-64598: In the Linux kernel, the following vulnerability has been resolved: smb/client: Fix error code…nvd · 2026-08-06
mediumCVE-2026-64598: smb/client: Fix error code in smb2_aead_req_alloc()msrc · 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
mediumCVE-2026-52967: smb/client: fix possible infinite loop and oob read in symlink_data()msrc · 2026-06-09