CVE-2026-9771
HighCVSS 8.8Exploitation Probability (EPSS)
Low risk1th percentile - higher than 1% of all known CVEs
Summary
A vulnerability in the flash_copy() system call in Zephyr RTOS (with CONFIG_USERSPACE enabled) allows an unprivileged thread to pass forged pointers to flash device structures. Lack of device object validation (src_dev, dst_dev) before dereferencing enables arbitrary code execution in supervisor mode, leading to privilege escalation outside the userspace sandbox.
Risk Assessment
An attacker with userspace access can gain full kernel control, resulting in privilege escalation, denial of service, or information disclosure. The vulnerability threatens the integrity and confidentiality of the entire system.
Recommendation
Update Zephyr RTOS immediately to a version containing the fix that adds K_SYSCALL_DRIVER_FLASH validation for both devices in z_vrfy_flash_copy(). If updating is not possible, disable CONFIG_USERSPACE or restrict access to the flash_copy() call for unprivileged threads.
Original NVD description (English source)
The flash_copy() system call is verified by z_vrfy_flash_copy() in drivers/flash/flash_util.c. On builds with CONFIG_USERSPACE enabled, this handler is the kernel-side trust boundary for a user-mode caller. Prior to the fix it validated only the output buffer (K_SYSCALL_MEMORY_WRITE) and passed the two struct device * arguments, src_dev and dst_dev, directly into the implementation without any object validation — unlike every sibling flash syscall, which guards its device pointer with K_SYSCALL_DRIVER_FLASH. A user-mode thread fully controls the values of src_dev/dst_dev and the contents of its own address space. The implementation z_impl_flash_copy() dereferences these pointers and calls through their driver-API function tables (e.g. api->get_parameters(dst_dev), flash_read(src_dev, ...), flash_write(dst_dev, ...)). By supplying a pointer to a forged struct device whose api table contains attacker-chosen function pointers, an unprivileged thread can cause the kernel to call arbitrary code in supervisor mode; passing any arbitrary or invalid address otherwise yields a kernel crash or out-of-bounds read. The result is a local privilege escalation out of the userspace sandbox (with kernel denial-of-service and information disclosure as lesser outcomes). The fix adds K_SYSCALL_DRIVER_FLASH(src_dev, read) and K_SYSCALL_DRIVER_FLASH(dst_dev, write) to z_vrfy_flash_copy(), which verify each device is a registered flash-driver kernel object the calling thread is permitted to use before any dereference, closing the path completely.