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

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

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@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.

The Linux kernel CVE team has assigned CVE-2026-74521 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.15 with commit e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 and fixed in 7.1.8 with commit d535363299822c5caa543787b21bd5cfa3e41949
	Issue introduced in 5.15 with commit e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 and fixed in 7.2-rc6 with commit e8bb506e6ef749ac0336f3e579d8d02396b7d832

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-74521
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/smb/server/smb2pdu.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/d535363299822c5caa543787b21bd5cfa3e41949
	https://git.kernel.org/stable/c/e8bb506e6ef749ac0336f3e579d8d02396b7d832