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FreeBSD-SA-26:28.capsicum Security Advisory
The FreeBSD Project
Topic: sigqueue(2) missing capability mode restriction
Category: core
Module: capsicum
Announced: 2026-06-09
Credits: Ed Maste
Affects: All supported versions of FreeBSD.
Corrected: 2026-05-29 19:11:40 UTC (stable/15, 15.1-STABLE)
2026-06-09 19:20:09 UTC (releng/15.1, 15.1-RC3-p1)
2026-06-09 19:19:46 UTC (releng/15.0, 15.0-RELEASE-p10)
2026-05-29 19:12:58 UTC (stable/14, 14.4-STABLE)
2026-06-09 19:19:08 UTC (releng/14.4, 14.4-RELEASE-p6)
2026-06-09 19:18:38 UTC (releng/14.3, 14.3-RELEASE-p15)
CVE Name: CVE-2026-45259
For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit .
I. Background
Capsicum is a lightweight OS capability and sandbox framework. It provides
two kernel primitives: capability mode, and capabilities. Capability mode
restricts the ability of a sandboxed process to interact with the global
namespace, including the ability to send signals to other processes, other
than via capability-based interfaces.
In capability mode, kill(2) restricts signal delivery to the calling process
only, preventing a sandboxed process from signalling other processes.
sigqueue(2) provides similar signal delivery functionality, and is similarly
permitted in capability mode.
II. Problem Description
sigqueue(2) was marked as permitted in capability mode with the introduction
of Capsicum in 2011, but the implementation of kern_sigqueue did not include
a capability mode check restricting signal delivery to the calling process's
own PID.
III. Impact
A process in capability mode can use sigqueue(2) to send signals to any
process it could signal following standard Unix permissions, bypassing the
Capsicum sandbox restriction. A compromised sandboxed process could
interfere with other processes, for example by sending SIGKILL or SIGSTOP.
This could be any process running as the same user, or any process, for a
superuser sandboxed process.
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 installed from base system packages:
Systems running a 15.0-RELEASE 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.
[FreeBSD 15.1]
# fetch https://security.FreeBSD.org/patches/SA-26:28/capsicum-15.1.patch
# fetch https://security.FreeBSD.org/patches/SA-26:28/capsicum-15.1.patch.asc
# gpg --verify capsicum-15.1.patch.asc
[FreeBSD 15.0]
# fetch https://security.FreeBSD.org/patches/SA-26:28/capsicum-15.0.patch
# fetch https://security.FreeBSD.org/patches/SA-26:28/capsicum-15.0.patch.asc
# gpg --verify capsicum-15.0.patch.asc
[FreeBSD 14.x]
# fetch https://security.FreeBSD.org/patches/SA-26:28/capsicum-14.patch
# fetch https://security.FreeBSD.org/patches/SA-26:28/capsicum-14.patch.asc
# gpg --verify capsicum-14.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
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/ defd9b86ef99 stable/15-n283744
releng/15.1/ 871d33e8a66a releng/15.1-n283553
releng/15.0/ 77ee83d12625 releng/15.0-n281055
stable/14/ d11ff01b3aec stable/14-n274231
releng/14.4/ eab757f954ed releng/14.4-n273717
releng/14.3/ f56e8cb94df6 releng/14.3-n271517
- -------------------------------------------------------------------------
Run the following command to see which files were modified by a
particular commit:
# git show --stat
Or visit the following URL, replacing NNNNNN with the hash:
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
The latest revision of this advisory is available at
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