CVE-2026-68119: tcp: initialize standalone TCP-AO response padding

CVE-2026-68119: tcp: initialize standalone TCP-AO response padding

[Greg Kroah-Hartman]

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

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

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

tcp: initialize standalone TCP-AO response padding

tcp_v4_send_ack() and tcp_v6_send_response() construct standalone TCP
responses with TCP-AO options.  The option length carries the actual MAC
length, but the TCP header length includes the option rounded up to a
four-byte boundary.

tcp_ao_hash_hdr() writes the MAC only.  Thus, when the MAC length is not
four-byte aligned, the one to three bytes after the MAC are left
uninitialized and may be transmitted.  For the normal TCP-AO hashing
mode, those bytes also have to be initialized before computing the MAC.

Initialize only the alignment padding in the TCP-AO branches, before
hashing the header.  Use TCPOPT_NOP, as in the normal TCP-AO output path.
This avoids adding work to non-AO TCP responses while preserving a valid
authenticated header.

The Linux kernel CVE team has assigned CVE-2026-68119 to this issue.


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

	Issue introduced in 6.7 with commit decde2586b34b99684faff1eab41e5c496c27fb6 and fixed in 6.12.101 with commit bbb7db8c74b0b5d17a695136f0f0806ecd0118f6
	Issue introduced in 6.7 with commit decde2586b34b99684faff1eab41e5c496c27fb6 and fixed in 6.18.42 with commit fadaff3f66e124c3a62237f9c881819a8ac90309
	Issue introduced in 6.7 with commit decde2586b34b99684faff1eab41e5c496c27fb6 and fixed in 7.1.6 with commit a859b280441fb02f64ed4037f03d5c0c34a7a595
	Issue introduced in 6.7 with commit decde2586b34b99684faff1eab41e5c496c27fb6 and fixed in 7.2-rc5 with commit e1a9d3cc11829c5414a75eb39c704f461936eb24

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-2026-68119
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:
	net/ipv4/tcp_ipv4.c
	net/ipv6/tcp_ipv6.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/bbb7db8c74b0b5d17a695136f0f0806ecd0118f6
	https://git.kernel.org/stable/c/fadaff3f66e124c3a62237f9c881819a8ac90309
	https://git.kernel.org/stable/c/a859b280441fb02f64ed4037f03d5c0c34a7a595
	https://git.kernel.org/stable/c/e1a9d3cc11829c5414a75eb39c704f461936eb24