Password guessing games with Check Point firewall

Two security flaws

Security researchers have discovered two potentially serious flaws with Check Point's flagship FireWall-1 firewall which give rise to both username guessing and sniffing issues.

First, affected versions permit attackers to determine if a firewall username is valid without having to know the associated password. This enabling crackers to guess valid usernames using a dictionary attack.

The guessing rate is limited mostly by the firewall CPU rather than by the Internet link speed, according to security testing specialists NTA Monitor, which discovered the problem. In effect, this means that companies using a hi-spec firewall server increase the speed at which an attacker can guess passwords, NTA
warns.

In addition, NTA Monitor discovered that VPN usernames are passed in the clear without encryption, allowing anyone who is able to sniff network traffic between VPN clients and the firewall to observe usernames in transit. The flaws exploit the Internet Key Exchange (IKE) encryption scheme and affect all Check Point FireWall-1 systems of 4.0 or above.

Roy Hills, Technical Director, NTA Monitor, said that the flaws leave a back door to enterprises "wide open to hackers".

"The biggest problem is that it is not necessary to send a password to obtain a reply from the Firewall. Given that both users and system administrators often chose weak passwords, it is likely that any attacker will be able to guess at least one password and thus gain access to the VPN - and from there most configurations easily allow full access to the company's resources."

Hills expressed surprise at discovering the flaw. He notes that it is standard security practice in many other authentication mechanisms, including Unix logon, to wait until both username and password are supplied before, if either is incorrect, sending a generic error message.

If certificates, rather than shared secrets, are used for IKE authentication, then neither problem occurs. However, NTA Monitor found that in practice the majority of users use shared secret authentication rather than certificates because they are easier to configure and better understood by both sysadmins and users.

Check Point has not responded to our request for comment at time of writing. ®

External Links

|NTA Monitor's alert which contains detailed technical descriptions of the problem

Sponsored: Designing and building an open ITOA architecture