Sunhillo SureLine before 9.1.5 contains an authentication bypass vulnerability that allows an unauthenticated remote attacker to impersonate any user with an active web session by forging a session cookie containing only a cleartext username with no random identifier or integrity protection. Attackers can guess default account names such as Admin or sftp_user and submit a forged username cookie to satisfy the login check in checkLogin (libwebcmn.so) and networkDiag.cgi, chaining into root command execution.