The remote host is vulnerable to a buffer overflow.
The remote host appears to be running a version of Apache, an open source web server. This version of Apache is vulnerable to a flaw in the 'htdigest' utilility. Specifically, a long user-supplied realm will cause an overflow and execution of arbitrary code. This issue is not considered a local flaw, as the program is not run setuid. An attacker exploiting this flaw would need to find a vulnerable Apache Web server that was making a call to 'htdigest' via a CGI script.
Upgrade or patch according to vendor recommendations.