CVE-2026-74521

Received Received - Intake

ksmbd ClientGUID Comparison Flaw via memcmp()

Publication date: 2026-08-15

Last updated on: 2026-08-17

Assigner: kernel.org

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.

CVSS Scores

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Meta Information

Published

2026-08-15

Last Modified

2026-08-17

Generated

2026-09-04

AI Q&A

2026-08-15

EPSS Evaluated

2026-09-03

NVD

CVE-2026-74521

EUVD

EUVD-2026-59714

Affected Vendors & Products

Vendor	Product	Version / Range
linux_kernel	ksmbd	*

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This vulnerability in the Linux kernel involves the ksmbd component where ClientGUID values are incorrectly compared using strncmp(). ClientGUID is a fixed-size binary value that may contain NUL bytes, which strncmp() does not handle properly, leading to incorrect equality checks between different values.

Detection Guidance

This vulnerability involves incorrect comparison of ClientGUID values in ksmbd due to the use of strncmp() instead of memcmp(). Detection requires checking if your Linux kernel uses a vulnerable version of ksmbd. Inspect kernel logs for ksmbd-related errors or check the kernel version with uname -r. If ksmbd is enabled, verify the code uses memcmp() for ClientGUID comparisons.

Impact Analysis

This vulnerability could allow attackers to bypass security checks by manipulating ClientGUID values, potentially enabling unauthorized access to SMB3 resources or session binding. Systems using ksmbd for SMB3 multichannel or FSCTL_VALIDATE_NEGOTIATE_INFO may be affected.

Compliance Impact

This vulnerability does not directly affect compliance with GDPR, HIPAA, or similar standards as it pertains to a specific implementation detail in the Linux kernel's ksmbd SMB server. Compliance impacts would depend on how the vulnerability is exploited in a real-world scenario, which is not described here.

Mitigation Strategies

Apply the latest kernel update that includes the fix for this issue. Disable ksmbd if not needed using modprobe -r ksmbd. Monitor vendor advisories for patches and update affected systems promptly to prevent potential unauthorized access or session manipulation.

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