From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-cve-announce@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@kernel.org>
Subject: CVE-2026-68118: tcp: challenge ACK for non-exact RST in SYN-RECEIVED
Date: Mon, 10 Aug 2026 13:57:15 +0200 [thread overview]
Message-ID: <2026081055-CVE-2026-68118-a409@gregkh> (raw)
From: Greg Kroah-Hartman <gregkh@kernel.org>
Description
===========
In the Linux kernel, the following vulnerability has been resolved:
tcp: challenge ACK for non-exact RST in SYN-RECEIVED
The SYN-RECEIVED request-socket path in tcp_check_req() accepts an
in-window RST without requiring SEG.SEQ to exactly match RCV.NXT. A
non-exact RST therefore removes the request instead of eliciting a
challenge ACK.
RFC 9293 section 3.10.7.4 applies the RFC 5961 reset check in
SYN-RECEIVED: an exact RST resets the connection, while a non-exact
in-window RST must trigger a challenge ACK and be dropped.
Apply that check before the ACK-field validation, following the RFC
sequence-number, RST, then ACK processing order. Factor the per-netns
challenge ACK quota out of tcp_send_challenge_ack() so request sockets
can share it. Use the request socket's send_ack() callback and its own
out-of-window ACK timestamp to send and rate-limit the response.
The Linux kernel CVE team has assigned CVE-2026-68118 to this issue.
Affected and fixed versions
===========================
Issue introduced in 3.6 with commit 282f23c6ee343126156dd41218b22ece96d747e3 and fixed in 6.18.42 with commit 234f9ffbd9b2c1b24ec67200ea3cff07401bec48
Issue introduced in 3.6 with commit 282f23c6ee343126156dd41218b22ece96d747e3 and fixed in 7.1.6 with commit 22cec809b048495310f206d9abbcdbbfbdce3ae3
Issue introduced in 3.6 with commit 282f23c6ee343126156dd41218b22ece96d747e3 and fixed in 7.2-rc5 with commit a28c4fcbf774e23b4779cae468e3497a5ad1f4a1
Issue introduced in 3.0.58 with commit 86791bbfe5ed7b275be040cfeff049a1624af1b7
Issue introduced in 3.2.37 with commit 61f69dc4e40e41b0018f00fa4aeb23d3239556fb
Issue introduced in 3.4.25 with commit 34fb350281ced2a72707a5c0064f69992d440edb
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-2026-68118
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:
include/net/tcp.h
net/ipv4/tcp_input.c
net/ipv4/tcp_minisocks.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/234f9ffbd9b2c1b24ec67200ea3cff07401bec48
https://git.kernel.org/stable/c/22cec809b048495310f206d9abbcdbbfbdce3ae3
https://git.kernel.org/stable/c/a28c4fcbf774e23b4779cae468e3497a5ad1f4a1
reply other threads:[~2026-08-10 12:02 UTC|newest]
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