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NVD / CVE Program· CNA Linux

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

Noroxi assessment

Priority: Monitor (action score 31/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.13% (FIRST EPSS).
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Linux Linux 27ead8c5418af6bfab711079fecb9414d78d4cae, 3eaec47518e126e6dcd1a48521d740278073f0ec, 550cfb8a81181331d4d0f76ab75ee58a0bf41e3e; azl3 kernel 6.6.152.1-1 on Azure Linux 3.0 Release Notes; azl3 kernel 6.6.157.1-1 on Azure Linux 3.0 Release Notes.

Low priority for now. Upgrade to Linux Linux 27ead8c5418af6bfab711079fecb9414d78d4cae, 3eaec47518e126e6dcd1a48521d740278073f0ec, 550cfb8a81181331d4d0f76ab75ee58a0bf41e3e; azl3 kernel 6.6.152.1-1 on Azure Linux 3.0 Release Notes; azl3 kernel 6.6.157.1-1 on Azure Linux 3.0 Release Notes or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

HighCVSS 7.8 · v3.1—No exploit Fix available
Published
Jul 25, 2026
Updated
Oct 30, 2026
EPSS
0.1% · 2th percentile

Report tools

JSON

Action score

31

Monitor

Low priority for now.

CVSS
31 / 40 · 7.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · Linux
7.8
NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-64388

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
linuxlinux kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • linux linux kernel4.18 and later · before 7.1.4

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 4.18affected
    • b326614ea2159ea5c835d320f261d05d080cd201 and later · before c0fe1118a1471d459f76c3e70ff2abbf784ce6bfaffected · git
    • b326614ea2159ea5c835d320f261d05d080cd201 and later · before 6825a45f6b8ef76b0ee32649ec3d6e39ca143a18affected · git
    • b326614ea2159ea5c835d320f261d05d080cd201 and later · before 27ead8c5418af6bfab711079fecb9414d78d4caeaffected · git
    • b326614ea2159ea5c835d320f261d05d080cd201 and later · before 3eaec47518e126e6dcd1a48521d740278073f0ecaffected · git
    • b326614ea2159ea5c835d320f261d05d080cd201 and later · before 550cfb8a81181331d4d0f76ab75ee58a0bf41e3eaffected · git
    • b326614ea2159ea5c835d320f261d05d080cd201 and later · before 760ef2c579c2609cf17fb1cd5392f64d42d43d33affected · git
    • before 4.18not affected · semver
    • 6.1.191 and later · up to and including 6.1.*not affected · semver
    • 6.6.160 and later · up to and including 6.6.*not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxfrom 0—
Debian:13linuxbefore 6.12.115-26.12.115-2
Debian:14linuxbefore 7.1.4-17.1.4-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
    90Now
  • CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV
    89Now
  • CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
    85Now

Published before and after this one in the same product

  • ← EarlierCVE-2026-64386Jul 25, 2026 · smb: client: fix query_info() replay double-free
    39Monitor
  • ← EarlierCVE-2026-64387Jul 25, 2026 · smb: client: fix query directory replay double-free
    39Monitor
  • Later →CVE-2026-64389Jul 25, 2026 · ksmbd: validate NTLMv2 response before updating session key
    32Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux27ead8c5418af6bfab711079fecb9414d78d4caeVendor (CNA)
Linux Linux3eaec47518e126e6dcd1a48521d740278073f0ecVendor (CNA)
Linux Linux550cfb8a81181331d4d0f76ab75ee58a0bf41e3eVendor (CNA)
Linux Linux6825a45f6b8ef76b0ee32649ec3d6e39ca143a18Vendor (CNA)
Linux Linux760ef2c579c2609cf17fb1cd5392f64d42d43d33Vendor (CNA)
Linux Linuxc0fe1118a1471d459f76c3e70ff2abbf784ce6bfVendor (CNA)
azl3 kernel 6.6.152.1-1 on Azure Linux 3.0Release NotesMicrosoft (MSRC)
azl3 kernel 6.6.157.1-1 on Azure Linux 3.0Release NotesMicrosoft (MSRC)
debian:linux6.12.115-2 · Debian:13Package registry (OSV)
debian:linux7.1.4-1 · Debian:14Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-4598859 days apartrxrpc: Fix re-decryption of RESPONSE packets
    39Monitor
  • CVE-2026-4624452 days apartnetfilter: nft_inner: Fix IPv6 inner_thoff desync
    36Monitor
  • CVE-2026-5321730 days apartnet: mvpp2: sync RX data at the hardware packet offset
    34Monitor
  • CVE-2026-5292031 days apartnetfilter: xt_policy: fix strict mode inbound policy matching
    33Monitor
  • CVE-2026-641766 days apartwifi: iwlwifi: mvm: fix driver-set TX rates on old devices
    32Monitor
  • CVE-2026-5319130 days apartio_uring/net: inherit IORING_CQE_F_BUF_MORE across bundle recv retries
    31Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-682 · Incorrect Calculation

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. SSVC exploitation— → none
  2. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (5 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records