From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-63995][MODERATE 7.0] ethtool: cmis: validate start_cmd_payload_size from module [ Upstream Date: Sun, 19 Jul 2026 18:27:15 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-63995 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: 63112b4515469d00008452d9cfe3fb3bf1aa2df3 List-Id: CVE: CVE-2026-63995 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: ethtool: cmis: validate start_cmd_payload_size from module [ Upstream Commit: 63112b4515469d00008452d9cfe3fb3bf1aa2df3 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=63112b4515469d00008452d9cfe3fb3bf1aa2df3 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63995 Analysis date: Sun, 19 Jul 2026 18:27:15 -0400 ActionableScore: 5 ActionableScore lower bound: 3 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A malicious or corrupted CMIS module can report an oversized firmware start payload size, causing the ethtool CMIS firmware update path to use it as a memcpy length and potentially perform an OOB write into a fixed-size kernel buffer. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-63995 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63995 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-2026-63995 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-805;Other CVSS 'AV:P/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H';BEST CVSS score: '6.6';DESCR 'A kernel out-of-bounds write can occur in the ethtool CMIS firmware update path because start_cmd_payload_size is read from the module CDB reply and later used as a memcpy length for a fixed size vendor_data buffer. A malicious or corrupted CMIS module can report an oversized value and cause memory corruption during the firmware-update start command. For the CVSS the PR:N is used for the paranoid score because the attacker does not need an OS account when the attack is modeled as a malicious physical module, but UI:R is kept because a firmware update operation normally has to be started by an administrator or management service. The issue is not network reachable in the usual IP sense and requires physical or supply-chain access to the module. Impact is at least denial of service via kernel memory corruption and in worst case may allow confidentiality or integrity impact due to an OOB write in kernel memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) YES WRITE OOB LINUS DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: **3** * Paranoid score: **5** * Final recommended bucket: **Actionable Moderate at minimum** ## 2. Signal breakdown **Triggered signals:** * **Firmware-mediated external influence: +1** The malformed value comes from the CMIS module CDB reply, so the attacker model is a malicious or corrupted optical module rather than ordinary network input. * **Memory corruption, strong corruption primitive: +2** The commit explicitly states that `start_cmd_payload_size` is used as a `memcpy` byte count and can cause an OOB write into a fixed-size kernel buffer. * **Privileged kernel/device-management memory corruption path: +1** The bug is in ethtool CMIS firmware update handling, a trusted device-management path using firmware/module-provided metadata. * **Availability impact realistic: +1** Kernel OOB writes can realistically lead to crash or corrupted kernel state. * **Weak LPE concern in paranoid score: +1** Because this is an OOB write in kernel memory, limited privilege-escalation concern is defensible, but there is no demonstrated arbitrary write, reclaim, or controlled target. **Subtracting signals:** * **Physical-only or rare hardware-only condition: -2** Practical exploitation requires a malicious or corrupted CMIS module, or supply-chain/control over module firmware behavior. * **Corruption primitive constrained or no attacker-controlled target: -1 in paranoid reasoning** The overwrite target appears to be a fixed CMIS CDB payload buffer, not an arbitrary kernel address. ## 3. Reachability analysis The issue is not remotely reachable over normal IP networking. The realistic attacker is a malicious or corrupted CMIS module that returns an oversized `start_cmd_payload_size`. Triggering the vulnerable path normally also requires a firmware update operation to be initiated through ethtool or a management service, which is typically privileged. Namespaces and containers do not substantially lower reachability unless a container or service is explicitly delegated access to the relevant netdevice and firmware-update operation. The path is not a default packet-processing path. It is reachable only on systems with CMIS-capable modules and CMIS firmware update support in use. Call-site confidence: **high**, because the commit directly states the value is later used as the `memcpy` byte count in `cmis_fw_update_start_download()` and identifies the fixed destination size. ## 4. Severity interpretation This is stronger than an ordinary Moderate because the patch fixes an explicitly described kernel OOB write. However, it is not a strong Important candidate by default because exploitation is hardware-mediated, requires a malicious or corrupted module, and likely requires an administrator or management workflow to start firmware update. Conservatively, this behaves like a constrained device-management memory corruption issue. Paranoid handling should keep it as **Actionable Moderate at minimum** because kernel OOB writes can sometimes become more serious than DoS, even when target control is not demonstrated. ## 5. One-sentence report phrase A malicious or corrupted CMIS module can report an oversized firmware start payload size, causing the ethtool CMIS firmware update path to use it as a memcpy length and potentially perform an OOB write into a fixed-size kernel buffer. ## 6. Manual review recommendation **MANUAL CHECK REQUIRED** Manual review is required because the patch explicitly describes a kernel OOB write. The main open question is exploitability depth: the primitive is constrained and hardware-mediated, but kernel memory corruption should not be auto-closed without checking the adjacent buffer layout and whether attacker-controlled firmware data can influence the overwrite contents. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ethtool: cmis: validate start_cmd_payload_size from module [ Upstream Commit: 63112b4515469d00008452d9cfe3fb3bf1aa2df3 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=63112b4515469d00008452d9cfe3fb3bf1aa2df3 Changed files: net/ethtool/cmis_fw_update.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=63112b4515469d00008452d9cfe3fb3bf1aa2df3 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-63995 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63995 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: 5 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: NO 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).