According to sudo.ws, sudo versions prior to 1.8.28 are affected due to potential bypass of Runas user restrictions. Please refer to https://www.sudo.ws/alerts/minus_1_uid.html for the detailed.
This was already fixed in buildroot master yesterday: https://git.buildroot.net/buildroot/commit/?id=4a96d627491dbf1ae622053068176ec27d3cdf60