CVE-2025-21783 is a vulnerability identified in the Linux kernel's GPIO (General Purpose Input/Output) subsystem, specifically within the gpiolib component. The issue arises in the function gpiochip_get_ngpios(), which is responsible for retrieving the number of GPIO lines managed by a GPIO chip. This function uses chip_*() macros to print diagnostic or error messages. However, these macros depend on the gpiodev structure being initialized and set. When gpiochip_get_ngpios() is invoked via the bgpio_init() function, gpiodev is not initialized, leading to a NULL pointer dereference when the chip_*() macros attempt to access it. This results in a kernel crash, causing a denial of service (DoS) condition. The fix replaces the chip_*() macros with dev_*() macros, which do not rely on gpiodev being initialized, thereby preventing the NULL pointer dereference and subsequent crash. This vulnerability is a logic error in error handling paths rather than a direct memory corruption or privilege escalation flaw. There are no known exploits in the wild at the time of publication, and no CVSS score has been assigned yet. The affected versions are identified by specific commit hashes, indicating the vulnerability is present in certain Linux kernel builds prior to the patch. The vulnerability affects the Linux kernel broadly, which is widely used in servers, desktops, embedded systems, and IoT devices worldwide.

For European organizations, the impact of CVE-2025-21783 primarily involves potential system instability and denial of service due to kernel crashes triggered by the vulnerability. Systems running vulnerable Linux kernel versions that utilize GPIO chips, particularly in embedded or industrial environments, could experience unexpected reboots or downtime. This can disrupt critical infrastructure, manufacturing processes, telecommunications equipment, or IoT deployments common in sectors such as automotive, energy, and healthcare. While the vulnerability does not directly lead to privilege escalation or data breaches, the resulting availability impact can affect operational continuity and service reliability. Organizations relying on Linux-based devices with GPIO interfaces should be aware that attackers or faulty software could trigger the crash, leading to service interruptions. The lack of known exploits reduces immediate risk, but the widespread use of Linux in Europe means that unpatched systems remain vulnerable to accidental or malicious triggering of this issue.

European organizations should take the following specific mitigation steps: 1) Identify all Linux systems running kernel versions that include the vulnerable gpiochip_get_ngpios() implementation, focusing on devices with GPIO hardware interfaces. 2) Apply the official Linux kernel patches that replace chip_*() macros with dev_*() macros in the gpiochip_get_ngpios() function as soon as they are available from trusted sources or distributions. 3) For embedded or IoT devices where kernel updates are challenging, consider isolating vulnerable devices from critical network segments to reduce the risk of remote triggering. 4) Implement monitoring for kernel crashes and system reboots that could indicate exploitation attempts or accidental triggering of this vulnerability. 5) Engage with hardware and software vendors to ensure timely firmware and kernel updates are provided and deployed. 6) Test patches in staging environments to verify stability before production deployment, especially in industrial control or critical infrastructure contexts. 7) Maintain robust incident response plans to quickly address any denial of service incidents related to this vulnerability.