linux-cve-announce - CVE-2025-40307: exfat: validate cluster allocation bits of the allocation bitmap

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Message-ID: <2025120820-CVE-2025-40307-40f1@gregkh>
Date: Mon,  8 Dec 2025 09:47:31 +0900
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40307: exfat: validate cluster allocation bits of the allocation bitmap

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

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

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

exfat: validate cluster allocation bits of the allocation bitmap

syzbot created an exfat image with cluster bits not set for the allocation
bitmap. exfat-fs reads and uses the allocation bitmap without checking
this. The problem is that if the start cluster of the allocation bitmap
is 6, cluster 6 can be allocated when creating a directory with mkdir.
exfat zeros out this cluster in exfat_mkdir, which can delete existing
entries. This can reallocate the allocated entries. In addition,
the allocation bitmap is also zeroed out, so cluster 6 can be reallocated.
This patch adds exfat_test_bitmap_range to validate that clusters used for
the allocation bitmap are correctly marked as in-use.

The Linux kernel CVE team has assigned CVE-2025-40307 to this issue.

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

	Fixed in 6.12.58 with commit 6bc58b4c53795ab5fe00648344aa7d9d61175f90
	Fixed in 6.17.8 with commit 13c1d24803d5b0446b3f6f0fdd67e07ac1fdc7bf
	Fixed in 6.18 with commit 79c1587b6cda74deb0c86fc7ba194b92958c793c

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-2025-40307
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/balloc.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/6bc58b4c53795ab5fe00648344aa7d9d61175f90
	https://git.kernel.org/stable/c/13c1d24803d5b0446b3f6f0fdd67e07ac1fdc7bf
	https://git.kernel.org/stable/c/79c1587b6cda74deb0c86fc7ba194b92958c793c