From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-63903][MODERATE REGULAR] USB: serial: belkin_sa: validate interrupt status length Date: Sun, 19 Jul 2026 20:32:32 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-63903 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: 2 X-AL-KERNEL-ActionableScore-Lower: 1 X-AL-KERNEL-Commit: f1617539ab90e67da788959bfd314076f093a11a List-Id: CVE: CVE-2026-63903 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: USB: serial: belkin_sa: validate interrupt status length Commit: f1617539ab90e67da788959bfd314076f093a11a Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f1617539ab90e67da788959bfd314076f093a11a Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63903 Analysis date: Sun, 19 Jul 2026 20:32:32 -0400 ActionableScore: 2 ActionableScore lower bound: 1 Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: A malformed Belkin USB serial device can return a short interrupt packet that causes belkin_sa_read_int_callback to read status bytes beyond the completed URB data, resulting in a kernel out-of-bounds read with mainly physical DoS exposure. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-63903 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63903 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-2026-63903 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:L/I:N/A:H';CWE-125;CWE-130;*CWE-20;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.2';DESCR 'The Belkin USB serial interrupt callback can read beyond the completed interrupt packet because it parses status bytes at fixed offsets 2 and 3 without first checking urb actual_length. A malicious or malformed USB serial device can return a short successful interrupt transfer or advertise a short interrupt endpoint, causing an out of bounds or stale status byte read in kernel context. For the CVSS the PR:N is used because no authenticated user privileges on the target are required once the attacker can present the USB device to the system. The attack is physical rather than network reachable, so AV:P is used. Impact is mainly denial of service via kernel fault or corrupted status handling. Confidentiality is at most limited because this is an invalid read without a demonstrated data disclosure path, and integrity impact is not supported by the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) YES READ KASAN OOB USB INIT PRINTF-TTY SIMPLEFIX LINUS PACKET NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ActionableScoreLower=1 ## 1. ActionableScore * Conservative score: 1 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate / Low-like**:: ## 2. Signal breakdown Triggered signals: * Firmware-mediated or device-mediated external influence: +1 A malicious or malformed USB serial device can influence interrupt URB contents and actual_length. * Weak memory safety issue: +0 to +1 The bug is a read-only out-of-bounds or stale status-byte read. It is not an OOB write, UAF, double free, type confusion, or controlled overwrite. * Reliable kernel crash / strong DoS: +0 conservative, +1 paranoid KASAN reports slab-out-of-bounds read. On production kernels this may only read stale adjacent data or corrupt status handling, but a crash is plausible in hardened/debug configurations or unlucky layouts. * Confidentiality impact plausible: +0 conservative, +1 paranoid A one-byte invalid kernel read exists, but there is no demonstrated disclosure path back to the attacker. Limited confidentiality concern is only a paranoid interpretation. Subtracted signals: * Physical-only or rare hardware-only condition: -2 Triggering requires presenting a malicious or malformed Belkin-compatible USB serial device or equivalent USB emulation. This is not remotely network reachable. No signals awarded: * No local unprivileged trigger in the normal syscall sense. * No privilege escalation primitive. * No generic strong memory corruption. * No integrity impact. * No broad network or common packet-processing exposure. ## 3. Reachability analysis The realistic attacker is someone who can attach or emulate a malicious USB serial device. No authenticated local user privileges are needed once the attacker can present the device, but the attack vector is physical or USB-device-mediated rather than remote. Namespaces and containers do not materially lower the requirement, because the vulnerable path is driven by kernel USB interrupt completion handling. The path is reachable only when the belkin_sa USB serial driver binds to a compatible device, so exposure is hardware-dependent and not broadly default-triggerable on all systems. Call-site confidence: high. The affected callback and the exact invalid access condition are visible in the patch context and KASAN trace. ## 4. Severity interpretation This behaves more like ordinary Moderate or Low-like physical attack surface than an Important-class kernel vulnerability. The theoretical memory-safety issue is real because KASAN confirms a slab out-of-bounds read, but the primitive is read-only, very small, device-specific, and lacks a demonstrated data disclosure or privilege-escalation path. The paranoid score keeps manual-review sensitivity because kernel OOB reads can hide layout-dependent behavior, but the practical exploitability is constrained by physical USB reachability. ## 5. One-sentence report phrase A malformed Belkin USB serial device can return a short interrupt packet that causes belkin_sa_read_int_callback to read status bytes beyond the completed URB data, resulting in a kernel out-of-bounds read with mainly physical DoS exposure. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Manual review is recommended because this is a confirmed kernel out-of-bounds read, but it is not an Important candidate by default because the primitive is read-only, physical/device-mediated, and has no demonstrated LPE or disclosure path. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: USB: serial: belkin_sa: validate interrupt status length Commit: f1617539ab90e67da788959bfd314076f093a11a Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f1617539ab90e67da788959bfd314076f093a11a Commit description: The Belkin interrupt callback treats interrupt data as a four-byte status report and reads LSR/MSR fields at offsets 2 and 3. The interrupt-in buffer length is derived from endpoint wMaxPacketSize, and short interrupt transfers may complete successfully with a smaller actual_length. Check the completed interrupt packet length before parsing status fields so short interrupt endpoints and short successful packets are ignored instead of causing out-of-bounds or stale status-byte reads. KASAN report as below: BUG: KASAN: slab-out-of-bounds in belkin_sa_read_int_callback() Read of size 1 Call trace: belkin_sa_read_int_callback() (drivers/usb/serial/belkin_sa.c:202) __usb_hcd_giveback_urb() (drivers/usb/core/hcd.c:1630) dummy_timer() (?:?) Fixes: 1da177e ("Linux-2.6.12-rc2") Assisted-by: Codex:gpt-5.5 Signed-off-by: Zhang Cen Cc: stable@vger.kernel.org Signed-off-by: Johan Hovold Signed-off-by: Greg Kroah-Hartman Changed files: drivers/usb/serial/belkin_sa.c drivers/usb/core/hcd.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=f1617539ab90e67da788959bfd314076f093a11a ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-63903 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63903 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:N/I:N/A:L The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H 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: 1 Paranoid ActionableScore: 2 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).