From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64540][MODERATE REGULAR] usbnet: gl620a: fix out-of-bounds read in genelink_rx_fixup() [ Upstream Date: Wed, 29 Jul 2026 01:06:45 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64540 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 3 X-AL-KERNEL-ActionableScore-Lower: 2 X-AL-KERNEL-Commit: 255d03551f94c7bdd86c7d9181a70b21917d829f List-Id: CVE: CVE-2026-64540 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: usbnet: gl620a: fix out-of-bounds read in genelink_rx_fixup() [ Upstream Commit: 255d03551f94c7bdd86c7d9181a70b21917d829f Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=255d03551f94c7bdd86c7d9181a70b21917d829f Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64540 Analysis date: Wed, 29 Jul 2026 01:06:45 -0400 ActionableScore: 3 ActionableScore lower bound: 2 Actionable bucket: Borderline manual review recommended / Actionable Moderate at minimum Manual review required: YES Summary: A malicious GeneLink GL620A USB network device can send malformed aggregated RX frames that make genelink_rx_fixup read past the received URB buffer and leak adjacent kernel heap data through the network stack. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64540 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64540 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 REGULAR 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-2026-64540 MODERATE CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L';CWE-125;CWE-126;*CWE-200;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N';BEST CVSS score: '5.2';DESCR 'A kernel heap information leak exists in the usbnet GeneLink (GL620A) receive path because genelink_rx_fixup can trust a device supplied packet length without checking that the claimed packet bytes are present in the received URB buffer. A malicious USB GeneLink device can send a short aggregated RX frame with a header that claims more data than was actually received, causing skb_put_data to copy past the end of the receive buffer and pass adjacent slab contents up the network stack. For the CVSS the PR:N is used because the attacker does not need a user account or privileges on the victim when the malicious USB device can supply RX frames to an active interface. The issue is not Internet network reachable and requires physical or local device level access to attach or control the USB network device. Impact is primarily confidentiality loss through kernel heap disclosure, with possible limited availability impact in the paranoid score, but no direct integrity impact or proven privilege escalation primitive is shown by this read only bug.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Actionable Moderate at minimum (with actual score 3) MAYBE READ KASAN OOB USB LEAK NETWORK SKB HARDWARE LINUS PACKET DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 ActionableScoreLower=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 3 * Final recommended bucket: **Borderline manual review recommended / Actionable Moderate at minimum** ## 2. Signal breakdown * Firmware-mediated external influence: +1 A malicious or controlled GL620A USB network device supplies the malformed RX frame contents. * Local or physical no-privilege trigger: +1 No user account on the victim is required once the malicious USB network interface is attached and active. * Confidentiality impact plausible: +1 The bug copies bytes past the received buffer and can pass adjacent kernel slab contents up the network stack. * Physical-only or rare hardware-only condition: -2 The attacker needs physical or equivalent device-level control of a specific USB GeneLink GL620A-style device path. * Rare and device-specific subsystem: -1 in the conservative view This is not a broad networking core path. It is limited to a specific legacy usbnet driver. * Paranoid adjustment: +1 Repeated attacker-controlled OOB reads from kernel heap via RX traffic justify manual review even though the primitive is read-only and physical-device scoped. ## 3. Reachability analysis The bug is triggered by a malicious GeneLink GL620A USB network device sending a short aggregated RX frame with a device-supplied packet length larger than the actual received data. It is not Internet network reachable and does not require a local Linux user account, but it does require physical access or an equivalent ability to emulate or control the USB device. Namespaces and containers do not materially lower the requirement because the vulnerable path is below userspace isolation, in the usbnet RX softirq. The path is only relevant when the affected USB network interface is present and active, so exposure is narrow compared with common TCP/IP or netfilter paths. ## 4. Severity interpretation This behaves like an actionable Moderate information disclosure issue, not an Important-class memory corruption bug. The demonstrated primitive is an out-of-bounds read and kernel heap disclosure, not an OOB write, UAF reclaim, type confusion, callback control, or privilege escalation primitive. The realistic impact is confidentiality loss from adjacent slab data exposure, with only limited paranoid availability concern. Because the primitive is attacker-controlled kernel heap disclosure, it should not be auto-closed without review despite the physical-device reachability constraint. ## 5. One-sentence report phrase A malicious GeneLink GL620A USB network device can send malformed aggregated RX frames that make genelink_rx_fixup read past the received URB buffer and leak adjacent kernel heap data through the network stack. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is a concrete attacker-controlled kernel heap out-of-bounds read and information leak, even though reachability is limited to physical or device-level access rather than remote network exposure. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: usbnet: gl620a: fix out-of-bounds read in genelink_rx_fixup() [ Upstream Commit: 255d03551f94c7bdd86c7d9181a70b21917d829f Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=255d03551f94c7bdd86c7d9181a70b21917d829f Changed files: drivers/net/usb/gl620a.c mm/kasan/shadow.c include/linux/skbuff.h drivers/net/usb/usbnet.c kernel/workqueue.c kernel/softirq.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=255d03551f94c7bdd86c7d9181a70b21917d829f ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64540 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64540 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:N/S:U/C:H/I:N/A:N The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L The Best / paranoid CVSS score: 5.2 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: 2 Paranoid ActionableScore: 3 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 REGULAR 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).