From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-63897][MODERATE REGULAR] USB: serial: mct_u232: fix missing interrupt-in transfer sanity check Date: Sun, 19 Jul 2026 18:18:43 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-63897 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: 1 X-AL-KERNEL-ActionableScore-Lower: 0 X-AL-KERNEL-Commit: 82b48d70bced1ec8e5f676d1fd5eccc7a44dc418 List-Id: CVE: CVE-2026-63897 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: USB: serial: mct_u232: fix missing interrupt-in transfer sanity check Commit: 82b48d70bced1ec8e5f676d1fd5eccc7a44dc418 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=82b48d70bced1ec8e5f676d1fd5eccc7a44dc418 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63897 Analysis date: Sun, 19 Jul 2026 18:18:43 -0400 ActionableScore: 1 ActionableScore lower bound: 0 Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: A missing interrupt-in length check in the USB serial mct_u232 driver may allow a malicious or faulty physical USB device to expose stale or uninitialized slab data to user space, causing a limited confidentiality impact without evidence of integrity impact, DoS, or privilege escalation. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-63897 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63897 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-63897 MODERATE CHECK WITH IMPACT FROM ORIG NN MODERATE 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:N';*CWE-200;*CWE-457;*CWE-20;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.6';DESCR 'A missing length check in the USB serial mct_u232 interrupt-in callback can make the driver parse data 0 and data 1 even when the device returned fewer than 2 bytes. A malicious or faulty MCT_U232 compatible USB device can trigger this by sending a short interrupt-in packet, causing stale or uninitialized slab data from the URB buffer to be interpreted and potentially exposed to user space. For the CVSS the PR:N is selected because no local account on the victim is required when the attacker can attach or control the USB device. The attack is not network reachable and is best modeled as physical device access. Impact is primarily confidentiality loss, with no supported evidence of integrity impact, kernel crash, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1) YES USB INIT PRINTF-TTY SIMPLEFIX LEAK IMPROVEONLY LINUS PACKET NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScoreLower=0 ActionableScore=1 ## 1. ActionableScore * Conservative score: 0 * Paranoid score: 1 * Final recommended bucket: **Ordinary Moderate / Low-like**:: ## 2. Signal breakdown Triggered signals: * Firmware-mediated external influence: +1 A malicious or faulty USB device can influence interrupt-in transfer length and return a short packet. * Confidentiality impact plausible: +1 The commit explicitly says stale or uninitialised slab data may be parsed and leaked to user space. Subtracted signals: * Physical-only or rare hardware-only condition: -2 The attacker needs physical access to attach or control a compatible USB serial device, or control of equivalent USB device emulation. Not triggered: * Remote reachable: +0 No network path is involved. * Local unprivileged trigger: +0 The trigger is not a normal local syscall-only path. It depends on USB device behavior. * Generic memory corruption: +0 This is an uninitialized or stale read/info leak, not UAF, OOB write, double free, or type confusion. * Privilege escalation plausible: +0 No overwrite, object replacement, callback control, refcount abuse, or other LPE primitive is shown. * Reliable kernel crash / strong DoS: +0 The patch addresses information exposure, not a demonstrated crash. ## 3. Reachability analysis The bug can be triggered by a malicious or malfunctioning MCT_U232-compatible USB serial device returning an interrupt-in packet shorter than 2 bytes. No local user account is required if the attacker can physically attach or emulate the USB device, but this is not remotely reachable over the network. Namespaces and containers do not materially lower the requirement because the relevant input comes from USB hardware behavior, not a namespaced userspace API. The affected driver is hardware-specific and only relevant when such a USB serial device is present and bound to this driver. Call-site confidence: high. The callback and the missing `urb->actual_length < 2` check are present in the provided patch. ## 4. Severity interpretation This behaves like a low-end information disclosure issue rather than an Important-class vulnerability. The theoretical concern is exposure of stale or uninitialized slab bytes to user space, but the patch does not show memory corruption, attacker-controlled overwrite, privilege escalation, or a crash primitive. The realistic impact is limited by physical USB-device access and by the small amount of status data parsed from the interrupt packet. ## 5. One-sentence report phrase A missing interrupt-in length check in the USB serial mct_u232 driver may allow a malicious or faulty physical USB device to expose stale or uninitialized slab data to user space, causing a limited confidentiality impact without evidence of integrity impact, DoS, or privilege escalation. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Manual review is reasonable because the issue involves possible kernel slab information exposure. It does not look urgent or Important-class because exploitation requires physical or emulated USB-device access and no memory corruption or privilege-escalation primitive is shown. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: USB: serial: mct_u232: fix missing interrupt-in transfer sanity check Commit: 82b48d70bced1ec8e5f676d1fd5eccc7a44dc418 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=82b48d70bced1ec8e5f676d1fd5eccc7a44dc418 Commit description: Add the missing sanity check on the size of interrupt-in transfers to avoid parsing stale or uninitialised slab data (and leaking it to user space). Fixes: 1da177e ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Reviewed-by: Greg Kroah-Hartman Signed-off-by: Johan Hovold Signed-off-by: Greg Kroah-Hartman Changed files: drivers/usb/serial/mct_u232.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=82b48d70bced1ec8e5f676d1fd5eccc7a44dc418 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-63897 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63897 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:L/I:N/A:N The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N The Best / paranoid CVSS score: 4.6 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: 0 Paranoid ActionableScore: 1 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).