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============================================================================= FreeBSD-SA-26:56.hwpmc Security Advisory
The FreeBSD Project

Topic: hwpmc fails to detach PMCs during exec credential transitions

Category: core
Module: hwpmc
Announced: 2026-08-25
Credits: Alexander Leidinger
Affects: All supported versions of FreeBSD.
Corrected: 2026-08-25 15:59:47 UTC (stable/15, 15.1-STABLE)
2026-08-25 16:01:17 UTC (releng/15.1, 15.1-RELEASE-p3)
2026-08-25 16:00:57 UTC (releng/15.0, 15.0-RELEASE-p13)
2026-08-25 16:00:00 UTC (stable/14, 14.4-STABLE)
2026-08-25 16:00:24 UTC (releng/14.4, 14.4-RELEASE-p9)
CVE Name: CVE-2026-58089

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 hwpmc(4) driver implements support for hardware performance
monitoring counters (PMCs). These counters can be used to collect
fine-grained performance data about a running process. Unprivileged
processes may attach PMCs to themselves or, subject to restrictions,
to other processes.

II. Problem Description

When a process calls execve(2) to execute a setuid or setgid image,
hwpmc(4) is supposed to detach PMCs owned by unprivileged processes.
An inverted check meant that this scenario was not handled properly.

III. Impact

An unprivileged local user who has attached PMCs to a process can
continue monitoring it after the process executes a setuid or setgid
binary, contrary to the intended policy.

IV. Workaround

No workaround is available. Systems that do not use hwpmc(4) are not
affected.

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.

[FreeBSD 15.x]
# fetch https://security.FreeBSD.org/patches/SA-26:56/hwpmc-15.patch
# fetch https://security.FreeBSD.org/patches/SA-26:56/hwpmc-15.patch.asc
# gpg --verify hwpmc-15.patch.asc

[FreeBSD 14.x]
# fetch https://security.FreeBSD.org/patches/SA-26:56/hwpmc-14.patch
# fetch https://security.FreeBSD.org/patches/SA-26:56/hwpmc-14.patch.asc
# gpg --verify hwpmc-14.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/ 87bb4aa63ac7 stable/15-n285143 releng/15.1/ e034ae898328 releng/15.1-n283598 releng/15.0/ 57a2373f86ac releng/15.0-n281101 stable/14/ 5eaecdb275d3 stable/14-n275045 releng/14.4/ 97e1e603bd40 releng/14.4-n273758
- -------------------------------------------------------------------------

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-2026-58089>

The latest revision of this advisory is available at <URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-26:56.hwpmc.asc> -----BEGIN PGP SIGNATURE-----

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