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FreeBSD-SA-26:67.ktls Security Advisory
The FreeBSD Project
Topic: Remote DoS via receive-side kernel TLS
Category: core
Module: ktls
Announced: 2026-09-29
Credits: Mark Johnston
Affects: All supported versions of FreeBSD.
Corrected: 2026-09-28 15:14:35 UTC (stable/15, 15.1-STABLE)
2026-09-29 16:00:11 UTC (releng/15.1, 15.1-RELEASE-p4)
2026-09-29 15:59:20 UTC (releng/15.0, 15.0-RELEASE-p14)
2026-09-28 16:20:36 UTC (stable/14, 14.5-STABLE)
2026-09-29 16:09:11 UTC (releng/14.5, 14.5-RELEASE-p1)
2026-09-29 15:57:28 UTC (releng/14.4, 14.4-RELEASE-p10)
CVE Name: CVE-2026-101302
For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit .
I. Background
Kernel TLS (KTLS) moves Transport Layer Security (TLS) record processing
into the kernel, allowing applications to encrypt and decrypt socket data
without copying it to and from userspace and to serve TLS data with
sendfile(2). When a connection uses software KTLS on the receive path,
the kernel decrypts each incoming TLS record in place within the socket
buffer.
II. Problem Description
TLS 1.3 embeds the actual record type as the last non-zero byte of the
decrypted payload, optionally followed by zero padding. The code which
searches for the inner record type had an off-by-one bug which could be
triggered by an invalid frame, leading to an underflow followed by an
unconditional NULL pointer dereference, causing a kernel panic.
III. Impact
A remote TLS 1.3 peer can send a specially crafted record to trigger a
kernel panic, resulting in a Denial of Service (DoS).
IV. Workaround
Only users running an application which enables receive-side KTLS
are affected. Systems with the kern.ipc.tls.enable sysctl set to 0
are unaffected.
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-26:67/ktls.patch
# fetch https://security.FreeBSD.org/patches/SA-26:67/ktls.patch.asc
# gpg --verify ktls.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/ 6d6a85c0be94 stable/15-n285662
releng/15.1/ a110070fd038 releng/15.1-n283624
releng/15.0/ 7092d9fe1c6b releng/15.0-n281123
stable/14/ fc1a02c93ba4 stable/14-n275236
releng/14.5/ 62af0c3351c1 releng/14.5-n274881
releng/14.4/ 11a5387a1290 releng/14.4-n273770
- -------------------------------------------------------------------------
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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