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FreeBSD-SA-26:48.compat32                                   Security Advisory
                                                          The FreeBSD Project

Topic:          Kernel stack disclosure in 32-bit compatibility support

Category:       core
Module:         kernel compat32
Announced:      2026-06-30
Credits:        Adam Crosser, Praetorian
Affects:        FreeBSD 14.3, FreeBSD 14.4 and FreeBSD 15.0
Corrected:      2026-03-20 13:36:44 UTC (stable/15, 15.0-STABLE)
                2026-06-30 17:21:36 UTC (releng/15.0, 15.0-RELEASE-p11)
                2026-03-20 19:35:28 UTC (stable/14, 14.4-STABLE)
                2026-06-30 17:21:08 UTC (releng/14.4, 14.4-RELEASE-p7)
                2026-06-30 17:20:42 UTC (releng/14.3, 14.3-RELEASE-p16)
CVE Name:       CVE-2026-49425

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

FreeBSD provides the compat32 subsystem, used to enable execution of 32-bit
binaries on 64-bit platforms.  System calls whose parameters require
translation are handled by compat32 before being dispatched to the native
system call handler.

II.  Problem Description

The compat32 kevent() handler translates a 64-bit kevent struct into a stack-
declared 32-bit struct.  It did not first zero the stack struct.

III. Impact

An unprivileged user may observe a small amount of uninitialized kernel
stack data, which may contain sensitive information.

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 the system.

Perform one of the following:

1) To update your vulnerable system installed from base system packages:

Systems running a 15.0-RELEASE or later version of FreeBSD on the amd64 or
arm64 platforms, which were installed using base system packages, can be
updated via the pkg(8) utility:

# pkg upgrade -r FreeBSD-base
# shutdown -r +10min "Rebooting for a security update"

2) To update your vulnerable system installed from binary distribution sets:

Systems running a RELEASE version of FreeBSD on the amd64 or arm64 platforms
which were not installed using base system packages can be updated via the
freebsd-update(8) utility:

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

3) 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.

# fetch https://security.FreeBSD.org/patches/SA-26:48/compat32.patch
# fetch https://security.FreeBSD.org/patches/SA-26:48/compat32.patch.asc
# gpg --verify compat32.patch.asc

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

# cd /usr/src
# patch -E -p0 < /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 as of the corresponding Git commit hash in the
following stable and release branches:

Branch/path                             Hash                     Revision
- -------------------------------------------------------------------------
stable/15/                              4551ea3b3f04    stable/15-n282670
releng/15.0/                            760b3f0b86a9  releng/15.0-n281081
stable/14/                              6a808cd75348    stable/14-n273827
releng/14.4/                            f145e3c02b46  releng/14.4-n273741
releng/14.3/                            495ee4943cd5  releng/14.3-n271541
- -------------------------------------------------------------------------

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

VII. References

<URL:https://www.cve.org/CVERecord?id=CVE-2026-49425>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-26:48.compat32.asc>
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