linux-cve-announce - CVE-2025-40287: exfat: fix improper check of dentry.stream.valid

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Message-ID: <2025120719-CVE-2025-40287-a68f@gregkh>
Date: Sun,  7 Dec 2025 06:52:34 +0900
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40287: exfat: fix improper check of dentry.stream.valid_size

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

exfat: fix improper check of dentry.stream.valid_size

We found an infinite loop bug in the exFAT file system that can lead to a
Denial-of-Service (DoS) condition. When a dentry in an exFAT filesystem is
malformed, the following system calls — SYS_openat, SYS_ftruncate, and
SYS_pwrite64 — can cause the kernel to hang.

Root cause analysis shows that the size validation code in exfat_find()
does not check whether dentry.stream.valid_size is negative. As a result,
the system calls mentioned above can succeed and eventually trigger the DoS
issue.

This patch adds a check for negative dentry.stream.valid_size to prevent
this vulnerability.

The Linux kernel CVE team has assigned CVE-2025-40287 to this issue.

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

	Fixed in 6.12.59 with commit 6c627bcc1896ba62ec793d0c00da74f3c93ce3ad
	Fixed in 6.17.9 with commit 204b1b02ee018ba52ad2ece21fe3a8643d66a1b2
	Fixed in 6.18 with commit 82ebecdc74ff555daf70b811d854b1f32a296bea

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-2025-40287
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/exfat/namei.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/6c627bcc1896ba62ec793d0c00da74f3c93ce3ad
	https://git.kernel.org/stable/c/204b1b02ee018ba52ad2ece21fe3a8643d66a1b2
	https://git.kernel.org/stable/c/82ebecdc74ff555daf70b811d854b1f32a296bea