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FreeBSD-SA-23:12.msdosfs                                    Security Advisory
                                                          The FreeBSD Project

Topic:		msdosfs data disclosure

Category:       core
Module:         msdosfs (FAT) file system driver
Announced:      2023-10-03
Credits:	Maxim Suhanov
Affects:        All supported versions of FreeBSD.
Corrected:      2023-07-18 05:46:13 UTC (stable/13, 13.2-STABLE)
                2023-10-03 21:23:40 UTC (releng/13.2, 13.2-RELEASE-p4)
                2023-09-11 18:51:21 UTC (stable/12, 12.4-STABLE)
                2023-10-03 22:15:40 UTC (releng/12.4, 12.4-RELEASE-p6)
CVE Name:       CVE-2023-5368

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.

I.   Background

The msdosfs driver provides read and write access to MS-DOS (FAT) file
systems.  Systems may be configured to allow unprivileged users to have
read and write access to mounted msdosfs file systems.

II.  Problem Description

In certain cases using the truncate or ftruncate system call to extend a
file size populates the additional space in the file with unallocated data
from the underlying disk device, rather than zero bytes.

III. Impact

A user with write access to files on a msdosfs file system may be able to
read unintended data (for example, from a previously deleted file).

IV.  Workaround

No workaround is available.

V.   Solution

Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date,
and reboot.

Perform one of the following:

1) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the amd64, i386, or
(on FreeBSD 13 and later) arm64 platforms can be updated via the
freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min "Rebooting for a security update"

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[FreeBSD 13.2]
# fetch https://security.FreeBSD.org/patches/SA-23:12/msdosfs.13.2.patch
# fetch https://security.FreeBSD.org/patches/SA-23:12/msdosfs.13.2.patch.asc
# gpg --verify msdosfs.13.2.patch.asc

[FreeBSD 12.4]
# fetch https://security.FreeBSD.org/patches/SA-23:12/msdosfs.12.4.patch
# fetch https://security.FreeBSD.org/patches/SA-23:12/msdosfs.12.4.patch.asc
# gpg --verify msdosfs.12.4.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

This issue is corrected by the corresponding Git commit hash or Subversion
revision number in the following stable and release branches:

Branch/path                             Hash                     Revision
- -------------------------------------------------------------------------
stable/13/                              868f3eadc5e0    stable/13-n255824
releng/13.2/                            7d08a7e6908b  releng/13.2-n254635
stable/12/                                                        r373207
releng/12.4/                                                      r373233
- -------------------------------------------------------------------------

For FreeBSD 13 and later:

Run the following command to see which files were modified by a
particular commit:

# git show --stat <commit hash>

Or visit the following URL, replacing NNNNNN with the hash:

<URL:https://cgit.freebsd.org/src/commit/?id=NNNNNN>

To determine the commit count in a working tree (for comparison against
nNNNNNN in the table above), run:

# git rev-list --count --first-parent HEAD

For FreeBSD 12 and earlier:

Run the following command to see which files were modified by a particular
revision, replacing NNNNNN with the revision number:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-5368>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-23:12.msdosfs.asc>
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