See how yeahlink compares to other vendors in security performance
Yealink phones through 2019-08-04 do not properly check user roles in POST requests. Consequently, the default User account (with a password of user) can make admin requests via HTTP.
Yealink phones through 2019-08-04 have an issue with OpenVPN file upload. They execute tar as root to extract files, but do not validate the extraction directory. Creating a tar file with ../../../../ allows replacement of almost any file on a phone. This leads to password replacement and arbitrary code execution as root.