CVE-2026-74270: handshake: Require admin permission for DONE command

CVE-2026-74270: handshake: Require admin permission for DONE command

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

handshake: Require admin permission for DONE command

ACCEPT and DONE are the two downcalls of the handshake genl
family, both intended for use by the trusted handshake agent
(tlshd). ACCEPT already requires GENL_ADMIN_PERM; DONE has
no privilege check at all.

The fd-lookup in handshake_nl_done_doit() only confirms that
some pending handshake request exists for the supplied sockfd;
it does not authenticate the sender. An unprivileged process
that guesses or observes a valid sockfd can therefore submit
a DONE with HANDSHAKE_A_DONE_STATUS == 0, leaving the kernel
consumer to proceed as if the handshake succeeded. A non-zero
status on a forged DONE tears down a legitimate in-flight
handshake before tlshd can report its real result.

The Linux kernel CVE team has assigned CVE-2026-74270 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.4 with commit 3b3009ea8abb713b022d94fba95ec270cf6e7eae and fixed in 6.6.145 with commit 25fb53e43ec006ac69b9e825a7e8a11d63a6083e
	Issue introduced in 6.4 with commit 3b3009ea8abb713b022d94fba95ec270cf6e7eae and fixed in 6.12.97 with commit b6557f912509abe8e70223373dd7a44d1d4a0d6c
	Issue introduced in 6.4 with commit 3b3009ea8abb713b022d94fba95ec270cf6e7eae and fixed in 6.18.40 with commit 67cec2f1eb9e58719d622e92e2278ceda72dbd85
	Issue introduced in 6.4 with commit 3b3009ea8abb713b022d94fba95ec270cf6e7eae and fixed in 7.1.5 with commit 4dafc411948469277b276724c3b2b4408c02c04c
	Issue introduced in 6.4 with commit 3b3009ea8abb713b022d94fba95ec270cf6e7eae and fixed in 7.2-rc1 with commit 81246a65303d9635266b1334490142caaf86a11f

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-74270
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	Documentation/netlink/specs/handshake.yaml
	net/handshake/genl.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/25fb53e43ec006ac69b9e825a7e8a11d63a6083e
	https://git.kernel.org/stable/c/b6557f912509abe8e70223373dd7a44d1d4a0d6c
	https://git.kernel.org/stable/c/67cec2f1eb9e58719d622e92e2278ceda72dbd85
	https://git.kernel.org/stable/c/4dafc411948469277b276724c3b2b4408c02c04c
	https://git.kernel.org/stable/c/81246a65303d9635266b1334490142caaf86a11f