Overview
CVE-2025-40263 addresses a vulnerability in the Linux kernel’s cros_ec_keyb driver. The flaw stems from a potential invalid memory access that can occur under specific conditions related to the initialization and event handling within the driver. Specifically, if cros_ec_keyb_register_matrix() isn’t called (due to the buttons_switches_only configuration) during the cros_ec_keyb_probe() function, the ckdev->idev pointer remains NULL. This leads to a crash when the cros_ec_keyb_process() function receives an EC_MKBP_EVENT_KEY_MATRIX event in the cros_ec_keyb_work() function.
Technical Details
The vulnerability manifests as an attempt to read from an unreadable memory address. The core issue lies in the fact that the cros_ec_keyb_work() function processes key matrix events without properly checking if the input device (ckdev->idev) has been initialized. The call trace reveals the sequence of events leading to the crash:
input_eventcros_ec_keyb_workblocking_notifier_call_chainec_irq_thread
The root cause is that even if the driver doesn’t intend to initialize the input device, the kernel might still receive malformed EC_MKBP_EVENT_KEY_MATRIX events, triggering the faulty memory access.
CVSS Analysis
Currently, a CVSS score is not available (N/A) for CVE-2025-40263. This is likely due to the specific conditions required to trigger the vulnerability. Further analysis is needed to determine the precise impact and exploitability. However, the ability to cause a kernel crash suggests a potential denial-of-service (DoS) condition. We will update this section when further information is available.
Possible Impact
The most likely impact of CVE-2025-40263 is a kernel crash, resulting in a denial-of-service (DoS). An attacker potentially could trigger this vulnerability by sending specially crafted input events to the cros_ec_keyb driver. This is especially concerning for systems where the `cros_ec_keyb` driver is active, even if it’s not fully initialized, such as embedded systems or laptops relying on this driver for keyboard functionality. While a full compromise of the system is not immediately evident, the crash can interrupt critical processes and require a reboot to recover.
Mitigation or Patch Steps
The vulnerability has been addressed in the Linux kernel. The fix involves ensuring that the cros_ec_keyb_process() function properly checks if ckdev->idev is NULL before attempting to access it. Users are strongly advised to update their Linux kernel to a version containing the fix. The specific commits addressing the vulnerability are listed in the References section below.
To mitigate the issue before patching, users might consider disabling the cros_ec_keyb driver if it’s not essential for their system. However, this might impact keyboard functionality on ChromeOS or similar devices that rely on this driver.
