From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3E3623DFC80 for ; Tue, 6 Oct 2026 10:26:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791282364; cv=none; b=jFxo83JEzvutyGDS+KdNfOFEdLIvbH8IobbkxT0r/4iz7pSKqmJtS0PwjK+PvatL8iJ8FOuCKxeG/A0zL6UjJkM8jwkAzczp1kT3bd5sKK9Qs9ATdhJHSO7uNWTfDIwIP5G26GRx5oWfpO+XjM5JRsB5zr4Iz1iDrz5M4eWK1xw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791282364; c=relaxed/simple; bh=UbFYOFbKM+X/AVhXCewFb5D9M/pOozt9MugLvNxIQXM=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=tesUTtgEiYTDeBEAZC+AxsyZULCin6SnqaDZETUlmnDQKhEONp42YCc+XDu0AjX+mfbxp29lyx0s9jqHWO2djEeUmpAptjGEL27zmmrSgp4tmwPLKp1w9L/w/LMD5dlw+UWdzozhGPNrm5yod7woeN561Nql0O9m5n+UgPk1iDA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=dKE9RnRZ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="dKE9RnRZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3A1921F000FF; Tue, 6 Oct 2026 10:26:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1791282362; bh=KssXeZ+oDKL9QdwKrtwUQ1RulBzMJ7+D1IknFtg6g8M=; h=From:To:Cc:Subject:Date:Reply-To; b=dKE9RnRZ4U0nNZad9+hnRmsUlijtcaSpW4SaTvEwRYKbBqb3S7OnIsGze7MZF7e7l 8Vot6eQVtNyDUSng7fmtmdrdSHK6l7eJDnVyyw8OvKmpEWpjBPyEJ1iL7zAzPgMcYY Lxo+wMzhl7wg6f7+jk6XzRqlBhY5N0zHw+idnocQ= From: Greg Kroah-Hartman To: linux-cve-announce@vger.kernel.org Cc: Greg Kroah-Hartman Subject: CVE-2026-98255: tcp: exclude old ACKs from tcp fast path Date: Tue, 6 Oct 2026 10:45:56 +0200 Message-ID: <2026100656-CVE-2026-98255-feaf@gregkh> X-Mailer: git-send-email 2.56.0 Reply-To: , Precedence: bulk X-Mailing-List: linux-cve-announce@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3728; i=gregkh@linuxfoundation.org; h=from:subject:message-id; bh=igB6OkbEvFcd62pGszv/w/27TIzNbzpWGWtnHUvCqbQ=; b=owGbwMvMwCRo6H6F97bub03G02pJDFlHtnLMeNdUdD59sgTnm2mv83lY2a+dDPG06Z9RMmF/f ITrrLh/HbEsDIJMDLJiiixftvEc3V9xSNHL0PY0zBxWJpAhDFycAjCRdFOG+VVlPKYrHv8OXSv3 hVUz6+DpJSeebmGYH/+732LPumWzZymFSlT6br7MEizmDAA= X-Developer-Key: i=gregkh@linuxfoundation.org; a=openpgp; fpr=F4B60CC5BF78C2214A313DCB3147D40DDB2DFB29 Content-Transfer-Encoding: 8bit From: Greg Kroah-Hartman Description =========== In the Linux kernel, the following vulnerability has been resolved: tcp: exclude old ACKs from tcp fast path Exclude old ACKs before SND.UNA from the tcp fast path as well as ACKs after SND.NXT. Such ACKs will fall through to the slow path, where tcp_ack() performs the appropriate validation and challenge ACK handling according to RFC5961 and Commit 3d501dd326fb1c7 ("tcp: do not accept ACK of bytes we never sent"). This prevents old ACKs from being accepted or modifying connection state as part of the fast path before appropriate ACK validation is applied. In particular, this prevents payload carried by a segment with an excessively old ACK from advancing RCV.NXT before the ACK is rejected. The Linux kernel CVE team has assigned CVE-2026-98255 to this issue. Affected and fixed versions =========================== Issue introduced in 4.14 with commit 31770e34e43d6c8dee129bfee77e56c34e61f0e5 and fixed in 5.10.271 with commit 07cacab90290f795bad2e566790f4ba8e84cdf5f Issue introduced in 4.14 with commit 31770e34e43d6c8dee129bfee77e56c34e61f0e5 and fixed in 5.15.222 with commit 6eb9b697f50b73b9684e466c1e97f4ca8e947a59 Issue introduced in 4.14 with commit 31770e34e43d6c8dee129bfee77e56c34e61f0e5 and fixed in 6.1.189 with commit b86e1e5a4bbcbbccde8b7a3d3486604b581f6628 Issue introduced in 4.14 with commit 31770e34e43d6c8dee129bfee77e56c34e61f0e5 and fixed in 6.6.158 with commit 1c8448db5cf35a13d82b0c9004ffdb49358883e7 Issue introduced in 4.14 with commit 31770e34e43d6c8dee129bfee77e56c34e61f0e5 and fixed in 6.12.112 with commit 8309dc2cc360056aa9cd2acfbfc25930798c3b66 Issue introduced in 4.14 with commit 31770e34e43d6c8dee129bfee77e56c34e61f0e5 and fixed in 6.18.54 with commit ff037920c688ae6ca1153fec01e90e6782712455 Issue introduced in 4.14 with commit 31770e34e43d6c8dee129bfee77e56c34e61f0e5 and fixed in 7.2.8 with commit 8205ac5ddb42a1843fa8d6a8c295b5c7f4f8c6ed Issue introduced in 4.14 with commit 31770e34e43d6c8dee129bfee77e56c34e61f0e5 and fixed in 7.3-rc4 with commit f81e6c3fb06327bc49cdd6e559845293ba06a704 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-2026-98255 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_input.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/07cacab90290f795bad2e566790f4ba8e84cdf5f https://git.kernel.org/stable/c/6eb9b697f50b73b9684e466c1e97f4ca8e947a59 https://git.kernel.org/stable/c/b86e1e5a4bbcbbccde8b7a3d3486604b581f6628 https://git.kernel.org/stable/c/1c8448db5cf35a13d82b0c9004ffdb49358883e7 https://git.kernel.org/stable/c/8309dc2cc360056aa9cd2acfbfc25930798c3b66 https://git.kernel.org/stable/c/ff037920c688ae6ca1153fec01e90e6782712455 https://git.kernel.org/stable/c/8205ac5ddb42a1843fa8d6a8c295b5c7f4f8c6ed https://git.kernel.org/stable/c/f81e6c3fb06327bc49cdd6e559845293ba06a704