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FreeBSD-SA-26:66.jail Security Advisory
The FreeBSD Project
Topic: Multiple jail filesystem root escapes
Category: core
Module: jail
Announced: 2026-09-29
Credits: Jan Bramkamp
Credits: firk
Affects: All supported versions of FreeBSD.
Corrected: 2026-09-29 15:56:24 UTC (stable/15, 15.1-STABLE)
2026-09-29 16:00:09 UTC (releng/15.1, 15.1-RELEASE-p4)
2026-09-29 15:59:18 UTC (releng/15.0, 15.0-RELEASE-p14)
2026-09-29 15:56:41 UTC (stable/14, 14.5-STABLE)
2026-09-29 16:09:09 UTC (releng/14.5, 14.5-RELEASE-p1)
2026-09-29 15:57:35 UTC (releng/14.4, 14.4-RELEASE-p10)
CVE Name: CVE-2026-101304, CVE-2026-101305, CVE-2026-101306
For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit .
I. Background
FreeBSD jails provide lightweight operating system virtualization and
confine processes to a restricted view of the filesystem. When a
directory file descriptor is passed between jails using SCM_RIGHTS
over a Unix domain socket, the receiving process's copy has the
FD_RESOLVE_BENEATH flag set, which restricts path lookups through
that descriptor to paths within the referenced directory.
II. Problem Description
Three flaws allow a jailed process to bypass FD_RESOLVE_BENEATH:
When fdescfs(4) was mounted in a jail with the "nodup" option, opening
/dev/fd/N returned a descriptor that did not inherit FD_RESOLVE_BENEATH or
the Capsicum capability rights of descriptor N. (CVE-2026-101304)
renameat(2) did not enforce FD_RESOLVE_BENEATH on its directory
arguments. A jailed process could rename a directory relative to a
restricted descriptor, then escape the jail root via fchdir(2).
This requires the directory to reside on a filesystem that is also
reachable from the jail's root. (CVE-2026-101305)
SCM_RIGHTS file descriptor passing did not preserve FD_RESOLVE_BENEATH
when a descriptor was transferred. A process could clear the restriction
by sending the descriptor to itself over a Unix domain socket.
(CVE-2026-101306)
III. Impact
A process in a jail that has received a directory file descriptor
from another jail can use these techniques to escape the jail's
filesystem root restriction.
IV. Workaround
No workaround is available, but systems that do not pass directory file
descriptors into jails 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 15.1]
# fetch https://security.FreeBSD.org/patches/SA-26:66/jail-15.1.patch
# fetch https://security.FreeBSD.org/patches/SA-26:66/jail-15.1.patch.asc
# gpg --verify jail-15.1.patch.asc
[FreeBSD 15.0]
# fetch https://security.FreeBSD.org/patches/SA-26:66/jail-15.0.patch
# fetch https://security.FreeBSD.org/patches/SA-26:66/jail-15.0.patch.asc
# gpg --verify jail-15.0.patch.asc
[FreeBSD 14.5]
# fetch https://security.FreeBSD.org/patches/SA-26:66/jail-14.5.patch
# fetch https://security.FreeBSD.org/patches/SA-26:66/jail-14.5.patch.asc
# gpg --verify jail-14.5.patch.asc
[FreeBSD 14.4]
# fetch https://security.FreeBSD.org/patches/SA-26:66/jail-14.4.patch
# fetch https://security.FreeBSD.org/patches/SA-26:66/jail-14.4.patch.asc
# gpg --verify jail-14.4.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
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/ 6c9ee5f02548 stable/15-n285682
releng/15.1/ 90d0b507cdf9 releng/15.1-n283622
releng/15.0/ 1406329089a0 releng/15.0-n281121
stable/14/ 666f08d59743 stable/14-n275243
releng/14.5/ e42a136d3945 releng/14.5-n274879
releng/14.4/ 9d0644e7a4f5 releng/14.4-n273776
- -------------------------------------------------------------------------
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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