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 89FC734F49F for ; Wed, 26 Aug 2026 14:41:37 +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=1787755298; cv=none; b=nhZCFC8/gj8Oab7XKa5FPF9pVHqsvfumnnspwbu6AuBAf1xsOONpotlH0SaWkHbIiJbeZIrkmSHAz4FusY9OPkIlQozhH27j032kTsosC/gLEwhTWR9gWQYJN6PQVkV0iV6cuNItfjxeMtlmE9UIIS09bFv8VP+bd3ONhe/QRf0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787755298; c=relaxed/simple; bh=MgP5z3TxXqmtfOq5Q/jqfNms8fHYJ/Iq9zZtkg566w4=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=Ob7HZ5opDSBlM/XF+/2jyCqkFIhLSfRIVzc84IoqfOoCeF9lAHrzDq/oUPCDuDDA0KeQQPPN3GBSVebG/NCYW6ZO2PA2Ym27XhYSmlL/bSNGpwiOXSn3pP/Xjf4T0TQjXvap9TxO6622SaBnLAb09Le4U5u2zCMJieot14JfB88= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=OZ38ZAGC; 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="OZ38ZAGC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E37981F00A3D; Wed, 26 Aug 2026 14:41:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1787755297; bh=8NXc4jI9kyv/BODJtIt1tCdmBMmsAZPFZp3T4oUs8e0=; h=From:To:Cc:Subject:Date:Reply-To; b=OZ38ZAGCNLEijtKYWiw/QxnVvGWwTnY4x2PkO8NWvv6VSbcMpe+T5ZWDrEe1d+eBj l7YtbdoNLoSDcKe6ewx+Vv8XC8QXh5QvDwavNUKRrrZcIOUHT70aR5eG6WUHVZLMqd xkNLkI3+XM8UOCMymymZpbplH5dfIPIG4zrWrMfI= From: Greg Kroah-Hartman To: linux-cve-announce@vger.kernel.org Cc: Greg Kroah-Hartman Subject: CVE-2026-80587: mptcp: avoid combining some incoming suboptions Date: Wed, 26 Aug 2026 16:38:23 +0200 Message-ID: <2026082616-CVE-2026-80587-425e@gregkh> X-Mailer: git-send-email 2.55.0 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=5767; i=gregkh@linuxfoundation.org; h=from:subject:message-id; bh=J6uiRRF/angdNI32Xp71bK232xtBWxu6whoX7DtNSuE=; b=owGbwMvMwCRo6H6F97bub03G02pJDFl9v2RSbT5cOiT+UpBtovUku8Pi6nJ+K/db1Fcq6S3VK A3PvlLYEcvCIMjEICumyPJlG8/R/RWHFL0MbU/DzGFlAhnCwMUpABPxvcswV8ZhV4JPbsGHJ35R tUdmCPakdIRdZZjvXlh/+O1mi8gDFXuyYh6cq83mk4wFAA== 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: mptcp: avoid combining some incoming suboptions Some MPTCP suboptions are mutually exclusive according to the RFC8684, but also because in different places, the code doesn't expect some combinations to be present. That's specially true for suboptions that would be present twice, but with different attributes. The new restrictions are the same as the ones applied on the output side, with mptcp_write_options. The same rules can be reused with a small fix: an MP_FASTCLOSE can be used with a DSS when the sender picks this option [1], which is not the case on Linux. Here are the rules: Which options can be used together? X: mutually exclusive O: often used together C: can be used together in some cases P: could be used together but we prefer not to (optimisations) | Opt: | MPC | MPJ | DSS | ADD | RM | PRIO | FAIL | FC | |------|------|------|------|------|------|------|------|------| | MPC |------|------|------|------|------|------|------|------| | MPJ | X |------|------|------|------|------|------|------| | DSS | X | X |------|------|------|------|------|------| | ADD | X | X | P |------|------|------|------|------| | RM | C | C | C | P |------|------|------|------| | PRIO | X | C | C | C | C |------|------|------| | FAIL | X | X | C | X | X | X |------|------| | FC | X | X | P | X | X | X | X |------| | RST | X | X | X | X | X | X | O | O | |------|------|------|------|------|------|------|------|------| The only difference is with the 'P': another stack could send and ADD_ADDR with other suboptions (DSS, RM_ADDR), and this should be allowed. A few points of attention: - In theory, an MP_CAPABLE could be used with a RM_ADDR, but there is no reason to add it with a SYN. Note that even with a 4th ACK, it doesn't seem to be useful, except when IDs are known in advance via another channel. Better not to break that. - Now, combining both an MP_CAPABLE and an MP_JOIN will no longer result to a reject of the two options, but only the second suboption is ignored. That seems OK to do that for this unexpected error. At least now all inconsistent combinations are handled the same way. This could change later in next. This also means the explicit checks for having both MPC + MPJ in subflow.c will now be unreachable. That's fine, they will be removed in a follow-up patch. - In case of conflicting combinations, the extra suboption(s) is/are ignored: having such combinations either means the remote peer is buggy, or is evil. The simplest action is then taken in this case: stop processing the current suboption. - In mp_opt->suboptions, there is also a bit reserved to the checksum, which can be used in an MP_CAPABLE and a DSS. Each time a DSS option can be used in parallel with another option, the checksum can be set, so the verification is combined into a new OPTIONS_MPTCP_DSS macro. - An MP_CAPABLE ACK can carry a Data-Level Length, and an optional Checksum: they are the same as the ones found in a DSS, because a DSS cannot be used in parallel to an MP_CAPABLE. Similarly, even if there is room, a DSS cannot be used with an MP_JOIN. The Linux kernel CVE team has assigned CVE-2026-80587 to this issue. Affected and fixed versions =========================== Issue introduced in 5.6 with commit eda7acddf8080bb2d022a8d4b8b2345eb80c63ec and fixed in 6.6.153 with commit dc1d8d3eb345c616fbe922a010fa391c72c54d52 Issue introduced in 5.6 with commit eda7acddf8080bb2d022a8d4b8b2345eb80c63ec and fixed in 6.12.105 with commit 099bfcbd0c16ae9b50aba2a1bea033e63f895da7 Issue introduced in 5.6 with commit eda7acddf8080bb2d022a8d4b8b2345eb80c63ec and fixed in 6.18.46 with commit a04dcc784959e4702048785d87e0d029bd2fbdcb Issue introduced in 5.6 with commit eda7acddf8080bb2d022a8d4b8b2345eb80c63ec and fixed in 7.1.10 with commit 6bab907292155513af397a12ccb488acbfc30d79 Issue introduced in 5.6 with commit eda7acddf8080bb2d022a8d4b8b2345eb80c63ec and fixed in 7.2 with commit b6ee361524641f57b2e2363f7737f20e17f67827 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-2026-80587 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/mptcp/options.c net/mptcp/protocol.h 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/dc1d8d3eb345c616fbe922a010fa391c72c54d52 https://git.kernel.org/stable/c/099bfcbd0c16ae9b50aba2a1bea033e63f895da7 https://git.kernel.org/stable/c/a04dcc784959e4702048785d87e0d029bd2fbdcb https://git.kernel.org/stable/c/6bab907292155513af397a12ccb488acbfc30d79 https://git.kernel.org/stable/c/b6ee361524641f57b2e2363f7737f20e17f67827