A vulnerability in the Linux kernel's libertas wifi driver caused a warning due to submitting a USB request block (URB) while it was still active. This issue occurred because the function usb_tx_block() did not ensure that a previous transmission had completed before submitting a new URB, potentially leading to a warning 'URB submitted while active'. The problem was fixed by enforcing serialization with usb_kill_urb() before submitting a new request.