The remote host is vulnerable to multiple attack vectors.
According to its banner, the remote host is running a version of phpBB that fails to sanitize user-supplied input. The details of several of these flaws is unknown; however, it is known that one of the vulnerabilities is an HTML injection flaw. This can enable an attacker to cause arbitrary HTML and script code to be executed in a user's browser within the context of the affected site.
Upgrade to version 2.0.22 or higher.