Often the algorithms to create those default passwords are weak. There are several instances of such algorithms having been reversed, allowing to crack such a default password with very few tries. Default passwords should not be trusted.
see for example those threads: https://hashcat.net/forum/thread-6170.html https://hashcat.net/forum/thread-4463.html
or this very detailed article documenting the reversing of one specific router: https://deadcode.me/blog/2016/07/01/UPC-...rsing.html
see for example those threads: https://hashcat.net/forum/thread-6170.html https://hashcat.net/forum/thread-4463.html
or this very detailed article documenting the reversing of one specific router: https://deadcode.me/blog/2016/07/01/UPC-...rsing.html