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FreeBSD-SA-26:57.unix                                       Security Advisory
                                                          The FreeBSD Project

Topic:          Use-after-free in unix SOCK_STREAM message handling

Category:       core
Module:         unix
Announced:      2026-08-25
Credits:        Mark Johnston
Affects:        FreeBSD 15.0 and later
Corrected:      2026-08-24 16:29:47 UTC (stable/15, 15.1-STABLE)
                2026-08-25 16:01:22 UTC (releng/15.1, 15.1-RELEASE-p3)
                2026-08-25 16:01:01 UTC (releng/15.0, 15.0-RELEASE-p13)
CVE Name:       CVE-2026-58090

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

Unix domain sockets provide a mechanism for processes on the same host
to communicate.  Processes can use unix domain sockets to exchange file
descriptors, using the SCM_RIGHTS control message type.

II.  Problem Description

The SOCK_STREAM receive path in the unix socket implementation
failed to fully detach control messages from the socket buffer before
processing them.  Some error paths would free those messages, leaving
freed data mbufs in the receive socket buffer.

III. Impact

An unprivileged local user can exploit this use-after-free to escalate
privileges.

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-26:57/unix.patch
# fetch https://security.FreeBSD.org/patches/SA-26:57/unix.patch.asc
# gpg --verify unix.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/                              06833c3e9813    stable/15-n285079
releng/15.1/                            0e4c26a82cb1  releng/15.1-n283602
releng/15.0/                            21de91422ca2  releng/15.0-n281105
- -------------------------------------------------------------------------

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-2026-58090>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-26:57.unix.asc>
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