From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-80586][IMPORTANT] mptcp: options: reset DSS fields in case of unexpected size Date: Wed, 26 Aug 2026 12:24:36 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-80586 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 6 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: 15e35fdad7a5576bf3f1c8d688877aeb5d1b506b List-Id: CVE: CVE-2026-80586 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: mptcp: options: reset DSS fields in case of unexpected size Commit: 15e35fdad7a5576bf3f1c8d688877aeb5d1b506b Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=15e35fdad7a5576bf3f1c8d688877aeb5d1b506b Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80586 Analysis date: Wed, 26 Aug 2026 12:24:36 -0400 ActionableScore: 6 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A remote MPTCP peer can send a malformed DSS option with an unexpected size that leaves stale parsed DSS fields for a following DSS or MPC with data, potentially causing MPTCP receive state inconsistency or uninitialized data access. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80586 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80586 The original announcement does not normally provide a security severity estimate, CVSS assessment, or enough information to determine whether the reported kernel bug represents a practically relevant security issue. This report was generated by AL-KERNEL, an AI-assisted Linux kernel vulnerability analysis system developed by Alexander Larkin. It combines an autonomous classifier with LLM-assisted technical analysis and a separate ActionableScore mechanism. The purpose of this report is to prioritize Linux kernel CVEs before manual review, identify cases that require prompt investigation, and support automatic closure of issues that are unlikely to have meaningful security impact. Published priority for this report: IMPORTANT Manual review required: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-80586 IMPORTANT CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';*CWE-457;*CWE-20;CWE-665;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '8.6';DESCR 'A remotely supplied malformed MPTCP DSS option with an unexpected size can be ignored after partially updating parsed option fields. A following DSS option or MPC with data may then be processed with stale or inconsistent flags such as use_map use_ack dsn64 ack64 or data_fin, which can lead to protocol state inconsistency or access to uninitialized data. For the CVSS the PR:N is selected because a peer only needs network reachability to an MPTCP endpoint and does not need a local account on the target. The issue is network reachable over MPTCP but exposure depends on whether MPTCP is enabled and reachable by untrusted peers. Impact is at least remote denial of service or connection state corruption, and worst case may allow limited confidentiality or integrity impact due to uninitialized data use. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) YES REMOTE SIMPLEFIX NETWORK LINUS KPANIC NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 6 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Remote reachable / network-triggerable: +2. A remote MPTCP peer can send a malformed DSS option with an unexpected size. * Memory corruption, weak/indirect corruption candidate: +1. The patch prevents stale partially written parser fields and possible uninitialized data access, but it does not show UAF, OOB write, arbitrary write, or controlled object reuse. * Availability impact realistic: +1. Malformed network input can create inconsistent MPTCP receive-path state and may plausibly cause connection or kernel-side failure. * Common networking receive/parser path: +1. This is in MPTCP TCP option parsing on the receive path. Paranoid additional signal: * Integrity impact plausible: +1. Stale DSS flags such as use_map, use_ack, dsn64, ack64, and data_fin may affect how later MPTCP options or data are interpreted, so limited protocol-state integrity impact is defensible. Not awarded: * No strong generic memory corruption +2. The patch does not demonstrate UAF, double free, OOB write, heap overwrite, arbitrary write, or type confusion. * No privilege escalation +2. There is no supported LPE primitive. * No strong confidentiality impact in the conservative score. Uninitialized data access is mentioned, but no concrete disclosure path is shown. * No admin privilege penalty. The trigger is from a remote peer, not a local privileged control interface. ## 3. Reachability analysis The likely trigger is a remote peer that can establish or interact with an MPTCP connection and send malformed DSS options. No local user account on the target is required for the network-triggered interpretation. Exposure depends on whether MPTCP is enabled and reachable by untrusted peers. It is not as broadly exposed as ordinary TCP parsing on every host, but it is still a network protocol receive path rather than a privileged local-only API. Namespaces and containers are not central to triggering because the relevant input is peer-supplied network traffic. Call-site confidence: medium. The patch shows the parser state reset at the malformed DSS size check, and the commit describes the follow-on DSS or MPC plus Data case, but the full downstream use of every stale field is not included. ## 4. Severity interpretation This is not an ordinary low-risk validation cleanup because the malformed input is remote and affects MPTCP option parser state. It is best treated as Actionable Moderate, with a Strong Important candidate flag for manual review if downstream analysis confirms kernel crash, disclosure, or stronger state corruption. The theoretical concern is stale parser state and uninitialized data use. The realistic evidence from the patch supports remote protocol-state inconsistency and possible DoS, but not proven arbitrary memory corruption or privilege escalation. ## 5. One-sentence report phrase A remote MPTCP peer can send a malformed DSS option with an unexpected size that leaves stale parsed DSS fields for a following DSS or MPC with data, potentially causing MPTCP receive state inconsistency or uninitialized data access. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the issue is network reachable in an MPTCP receive parser and involves stale parser state plus possible uninitialized data access, so it should not be auto-closed without checking downstream field usage and crash or disclosure potential. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: mptcp: options: reset DSS fields in case of unexpected size Commit: 15e35fdad7a5576bf3f1c8d688877aeb5d1b506b Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=15e35fdad7a5576bf3f1c8d688877aeb5d1b506b Commit description: A remote peer could send a malformed DSS with a wrong size, followed by another DSS or MPC + Data. In this case, the first suboption will be ignored, but leaving some fields written, which could lead to inconsistency or access uninitialized data. Explicitly reset the fields that could have been modified in case of unexpected size. Link: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260728-net-mptcp-misc-fixes-7-2-rc6-v1-0-f7e2d229159d%40kernel.org?part=1 Fixes: 648ef4b ("mptcp: Implement MPTCP receive path") Cc: stable@vger.kernel.org Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260803-net-mptcp-misc-fixes-7-2-rc6-v2-1-b8f496d71664@kernel.org Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: net/mptcp/options.c Diff excerpt: Not included in this email. See the upstream URL for the full patch. Full patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=15e35fdad7a5576bf3f1c8d688877aeb5d1b506b ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80586 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80586 The original CVE announcement normally does not include a security-level estimate. In particular, it may not contain a CVSS assessment, an impact level, or enough information to determine whether the reported bug is a practically relevant security issue. One purpose of this parallel CVE list is to provide that missing technical and prioritization information. The original goal of the AL-KERNEL project was to prioritize Linux kernel CVE analysis automatically before manual review. The system can also help identify non-security issues that may be suitable for automatic closure. This report was generated by AL-KERNEL, an AI-assisted Linux kernel vulnerability analysis system developed by Alexander Larkin. The first analysis stage combines an autonomous classifier with additional LLM-based analysis. The autonomous classifier runs locally on a CPU and is based on a backpropagation neural network. Together, these mechanisms produce a technical vulnerability description, identify likely weakness types, estimate CVSS severity, and provide input for ActionableScore. Two CVSS estimates are retained because incomplete kernel vulnerability information often permits more than one defensible interpretation: Conservative CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 8.6 The conservative vector represents a lower-impact interpretation. The Best/paranoid vector intentionally represents a plausible upper-bound interpretation and should not automatically be treated as demonstrated real-world impact. CVSS may also need to be adjusted for a particular Linux deployment, because actual reachability, privileges, enabled kernel configuration, hardware, namespaces, exposed device nodes, and other environmental conditions can differ significantly between systems. A separate ActionableScore mechanism evaluates practical remediation urgency. Its analysis may include reachability, attack prerequisites, subsystem exposure, memory-corruption characteristics, denial-of-service reliability, and possible confidentiality, integrity, or privilege-escalation impact. Conservative ActionableScore: 5 Paranoid ActionableScore: 6 The final base severity is taken directly from the second tab-separated field of the AL-KERNEL classification result. ActionableScore does not replace or independently override that final AL-KERNEL decision, and if ActionableScore adjusted impact level of ALKERNEL, then you would see self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7. For an AL-KERNEL result of MODERATE, this report uses the following additional presentation split: ActionableScore below 5 -> MODERATE REGULAR ActionableScore 5 or more -> MODERATE 7.0 The distinction between MODERATE REGULAR and MODERATE 7.0 makes it possible to identify Moderate issues that should receive manual analysis and fixes before lower-priority MODERATE REGULAR issues. In many cases, MODERATE REGULAR fixes may wait for a later rebase or routine update. There is one override in which MODERATE REGULAR becomes MODERATE 7.0 even when the ActionableScore is below 5. When the AL-KERNEL result contains the KPANIC flag, a MODERATE result is always presented as MODERATE 7.0. The KPANIC flag selected with few regexps without usage of AI at all, so it helps to detect cases when Kernel Crash happens and similar (to filter False-Negative results from the LLM usage). KPANIC indicates that a reliable kernel crash, kernel panic, or similarly serious kernel availability impact was identified by the classification workflow. AL-KERNEL base severity for this report: IMPORTANT KPANIC detected for this report: YES Published priority for this report (same as in Subject): IMPORTANT These results are intended to support engineering triage. They are machine-generated estimates, and cases marked for manual review should be validated by a human security engineer before final disposition. For more info read docs linked from here: https://kernelcve.org/ (and you can submit you own patch there to generate such a report for non-existant CVE-id yet). Note that in many cases this AI tool selects higher severity, than real is (means you can expect Importants instead of Moderate 7.0 or Moderates 7.0 instead of regular Moderates). If you see such cases, please use reply email interface to add additional manual analyses info to this particular CVE. And please, please, let me know when you see Lows instead of Importants or Important instead of Low (because particular for such cases I need to tune this AI tool to make it better for this one and next similar). My contact email for such notifications is alexanjelausa@gmail.com (and both send reply to CVE record itself too and see "reply" button below for howto reply).