From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-63996][MODERATE 7.0] ethtool: cmis: require exact CDB reply length [ Upstream Date: Sun, 19 Jul 2026 16:24:16 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-63996 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 6 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: 2f818cc98fd2c63a08239cb48995f6c3bfe9d9b3 List-Id: CVE: CVE-2026-63996 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: ethtool: cmis: require exact CDB reply length [ Upstream Commit: 2f818cc98fd2c63a08239cb48995f6c3bfe9d9b3 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2f818cc98fd2c63a08239cb48995f6c3bfe9d9b3 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63996 Analysis date: Sun, 19 Jul 2026 16:24:16 -0400 ActionableScore: 6 ActionableScore lower bound: 3 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A malicious or faulty CMIS SFP module can report an overlong CDB reply length, causing ethtool CMIS reply handling to process data beyond the expected buffer and potentially trigger kernel OOB writes, with realistic impact ranging from host DoS to worst-case kernel memory corruption. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-63996 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63996 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: MODERATE 7.0 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-2026-63996 MODERATE CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H';*CWE-787;*CWE-20;CWE-1284;Other CVSS 'AV:P/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H';BEST CVSS score: '6.6';DESCR 'CMIS CDB reply handling in ethtool can trust a reply length reported by an attached SFP module and process a payload longer than the buffer allocated for the expected reply. A malicious or faulty module can return an overlong rpl_len for a fixed layout CDB response, which can lead to an OOB write in kernel memory and may cause a crash or potentially stronger memory corruption impact. For the CVSS the PR:N is used for the paranoid score because the attacker model is a malicious attached module or supply-chain device that does not need a local account on the host, although a host ethtool or management query may be needed to exercise the path. The issue is not network reachable. Impact is at least denial of service and worst case may include confidentiality and integrity impact due to the OOB write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5) YES WRITE OOB IMPROVEONLY LINUS KPANIC KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 6 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Firmware-mediated external influence: +1. The attacker-controlled input is the CMIS CDB reply from a malicious or faulty SFP module. * Memory corruption, strong corruption primitive: +2. The commit explicitly says an overlong `rpl_len` can lead to OOB writes. * Privileged kernel/device-management memory corruption path: +1. The corruption occurs in trusted kernel device-management code handling transceiver firmware/module data. * Reliable kernel crash / strong DoS: +1. Kernel OOB writes can realistically crash the host. * Physical-only or rare hardware-only condition: -2. Practical triggering requires a malicious, compromised, or faulty physical SFP/CMIS module. Paranoid added signals: * Weak LPE concern: +1. OOB write in kernel memory can theoretically become more than DoS, although no controlled target or exploit chain is shown. * Confidentiality impact plausible: +1. In the worst case, kernel memory corruption could affect confidentiality. * Integrity impact plausible: +1. In the worst case, kernel memory corruption could affect integrity. Call-site confidence: high. The commit identifies affected callers and explains that `page_data->length` is derived from `rpl_exp_len`, while `rpl->hdr.rpl_len` is module supplied. ## 3. Reachability analysis The bug is not network reachable. The realistic attacker model is a malicious, compromised, counterfeit, or faulty SFP/CMIS module returning an overlong CDB reply. A host-side ethtool or management query is likely needed to exercise the path, but the attacker does not necessarily need a local account on the host if the malicious device is already attached. Namespaces and containers do not materially improve reachability because the primary influence is firmware or hardware mediated rather than a normal local userspace API. This is not a default Internet-exposed path. It is most relevant in data-center or networking environments using CMIS-capable pluggable modules. ## 4. Severity interpretation This is stronger than an ordinary Moderate because the patch explicitly addresses kernel OOB writes, not just a warning or validation cleanup. Realistic exploitation is constrained by physical or supply-chain access to an SFP module and by the need for the host to query the module. The practical impact may often be DoS, but the memory-corruption primitive is serious enough to avoid auto-closure. The conservative view is borderline due to physical-only reachability. The paranoid view is Actionable Moderate because an attacker-controlled device can influence a kernel OOB write in a trusted device-management path. ## 5. One-sentence report phrase A malicious or faulty CMIS SFP module can report an overlong CDB reply length, causing ethtool CMIS reply handling to process data beyond the expected buffer and potentially trigger kernel OOB writes, with realistic impact ranging from host DoS to worst-case kernel memory corruption. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the patch explicitly fixes an OOB write condition in kernel memory. Even though exploitation is constrained by malicious or faulty physical hardware, this class should be manually reviewed and should not be auto-closed. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ethtool: cmis: require exact CDB reply length [ Upstream Commit: 2f818cc98fd2c63a08239cb48995f6c3bfe9d9b3 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2f818cc98fd2c63a08239cb48995f6c3bfe9d9b3 Changed files: net/ethtool/cmis_cdb.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=2f818cc98fd2c63a08239cb48995f6c3bfe9d9b3 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-63996 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63996 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:P/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 6.6 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: 3 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: MODERATE KPANIC detected for this report: YES Published priority for this report (same as in Subject): MODERATE 7.0 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).