A recent post on Bugtraq has revealed a serious flaw in the core design of the freely-available personal firewall ZoneAlarm running on MS Windows. Thanks to the Win32 ShellExecute function in Windows, ZoneAlarm could theoretically be tweaked into opening an unsecured Internet connection and leaking information into web servers anywhere.
By introducing a Trojan into a user computer, hackers could theoretically force an Internet connection bypassing the security of the freeware firewall, provided of course that the affected user, just idly clicked on the product's pop ups without reading them. Of course, for the attack to be successful in the first place, malware would have to be introduced. But this can often be as simple as sending an infected attachment.
Although the attack has yet to be deployed in the wild, it could potentially be used to easily bypass the supposed security of the freeware version of ZoneAlarm and leave millions of users data exposed to anyone who wants it.
ZoneLabs points out that the bug was only tested on version 3.1 of ZoneAlarm (it is now up to 3.7); but in principle even this is subject to the same vuln.
Because this is an error at core programming level a patch would be hard to find for the freeware version of ZoneAlarm. If you pay for ZoneAlarm Pro ('Limited Time Offer! Only $39.95!") and tweak a few program properties, Hey Presto! the holes are filled.
The best advice for avoiding this bug is to keep your eyes peeled for malware. Also, look out for prompts from the freely distributed ZoneAlarm, and follow the guidance of ZoneLabs "to update all security products to the latest releases whenever updates become available". In the interim, ZoneLabs is currently hard at work resolving this bug and hardening security in the freeware version. ®