A firewall is used by Anti Virus Support to prevent unwanted access to network services. It is geared to the address of the communication partners ( ie, “who is allowed to access what “). As a rule, can not prevent the exploitation of a vulnerability in the Network Service.
When utilizing the backward path, it cannot protect against access to vulnerabilities, if the communication partner can access the vulnerable areas of the program. Therefore, programs that are intended for network access, must be kept up to date to close known vulnerabilities. Some firewalls provide filters that limit the remote access to the used network service by, for example, the filtering of vulnerable ActiveX objects from web pages.
The browser can then no longer access embedded Web page objects, which also means that it can not be attacked via these objects. Alternatively, this behavior can also be reached through the configuration of the browser.