The remote host is vulnerable to a local flaw in the way that it creates temporary files.
The remote host is running a vulnerable version of Acme thttpd. It is reported that versions prior to 2.24 are prone to a local flaw where temporary files can be used by local users to escalate their privileges on the machine. Specifically, attackers can use the insecure temp files to overwrite critical web content or configuration files.
Upgrade to version 2.24 or higher.