CVE-2025-40020: 
Linux Kernel vulnerability analysis and mitigation

CVE-2025-40020 was published on October 24, 2025, affecting the Linux kernel's PEAK-System CAN-USB FD driver. The vulnerability involves a shift-out-of-bounds issue in the can: peak_usb driver where a 32-bit shift operation is performed on what should be a 64-bit constant (NVD).

The vulnerability stems from an incorrect bit shifting operation in the Linux kernel's CAN-USB FD driver. The issue occurs when the driver performs a 32-bit shift operation instead of using a 64-bit constant, which is required for PC CAN FD interfaces. The fix involves explicitly using a 64-bit constant (1ULL) instead of a 32-bit value (1) to prevent overflow during shifting operations. The vulnerability has been assigned a CVSS v3.1 base score of 5.5 (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H) indicating moderate severity (Red Hat).

The vulnerability's impact is primarily limited to incorrect timestamp calculations and potential driver instability when using PEAK-System CAN-USB FD adapters. The issue affects system stability but does not compromise confidentiality or integrity of the system (Red Hat).

The vulnerability has been fixed in several Linux distributions. Ubuntu has marked it as medium priority and is working on updates for affected versions. Debian has fixed the issue in version 6.16.10-1 and later releases. Red Hat has deferred fixes for RHEL versions 7, 8, 9, and 10 (Ubuntu, Debian, Red Hat).