Wordpress(wp-users)

UPDATE wp_users SET user_pass =md5( '123456') WHERE user_login = 'admin';

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Joomla(jos_users)

UPDATE jos_users SET password='21232f297a57a5a743894a0e4a801fc3' WHERE username='admin';

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PHPBB(phpbb_users)

UPDATE phpbb_users SET user_password = MD5('abcd1234') WHERE username = 'phpbb_admin';