CVE-2025-21746 is a vulnerability identified in the Linux kernel related to the handling of the Synaptics touchpad driver, specifically when enabling a pass-through port. The issue arises because an interrupt may occur before the psmouse driver binds to the pass-through port. The Synaptics sub-driver attempts to access the psmouse instance associated with the pass-through port to determine whether to forward only a single byte of response or the entire protocol packet. However, if the psmouse instance has not yet been attached to the port, this access attempt can cause the driver to crash. The root cause is a race condition between the interrupt and the binding of the psmouse driver to the port. The fix involves introducing open() and close() methods for the port and checking if the port is open before accessing the psmouse instance. Since psmouse calls serio_open() only after attaching the psmouse instance to the serio port, this prevents the crash by ensuring the driver only accesses the psmouse instance when it is properly initialized. This vulnerability is a stability and reliability issue rather than a direct code execution or privilege escalation flaw. It can lead to denial of service (DoS) conditions by crashing the input device driver, potentially affecting system usability and availability. There are no known exploits in the wild, and no CVSS score has been assigned yet. The affected versions are identified by specific commit hashes, indicating this is a recent kernel-level fix.

For European organizations, the primary impact of CVE-2025-21746 is a potential denial of service on systems running vulnerable Linux kernel versions with Synaptics touchpad drivers. This could disrupt user input devices, causing system instability or crashes, particularly on laptops and embedded devices using Synaptics hardware. Organizations relying on Linux-based endpoints, workstations, or servers with Synaptics touchpads may experience reduced productivity or operational interruptions. While this vulnerability does not directly lead to data breaches or privilege escalation, the resulting system crashes could be exploited in targeted denial of service attacks, especially in environments where continuous availability is critical. In sectors such as finance, healthcare, and critical infrastructure within Europe, such disruptions could have cascading effects on business continuity and service delivery. However, since no known exploits exist and the vulnerability requires a specific hardware and driver configuration, the overall risk is moderate but should not be ignored.

European organizations should prioritize updating their Linux kernel to the patched versions that include the fix for CVE-2025-21746. Specifically, kernel maintainers and system administrators should apply the patch that introduces open() and close() methods for the pass-through port and adds checks before accessing the psmouse instance. For environments where immediate patching is not feasible, organizations can mitigate risk by disabling the Synaptics pass-through port feature if it is not required, thereby avoiding the race condition. Additionally, monitoring system logs for driver crashes related to psmouse or Synaptics can help detect attempts to trigger this vulnerability. Organizations should also ensure robust endpoint protection and system monitoring to detect unusual input device behavior or system instability. Finally, maintaining an up-to-date inventory of hardware and kernel versions will help identify systems at risk and prioritize remediation efforts.