phpIPAM version 1.5.1 contains a vulnerability where an attacker can bypass the IP block mechanism to brute force passwords for users by using the \'X-Forwarded-For\' header. The issue lies in the \'get_user_ip()\' function in \'class.Common.php\' at lines 1044 and 1045, where the presence of the \'X-Forwarded-For\' header is checked and used instead of \'REMOTE_ADDR\'. This vulnerability allows attackers to perform brute force attacks on user accounts, including the admin account. The issue is fixed in version 1.7.0.