This indicates an attack attempt to exploit a code-execution vulnerability in Realnetworks Helix Server.
The vulnerability is caused by improper bounds checking in the
NTLM authentication function. By sending a specially crafted HTTP request, a remote attacker could execute arbitrary code on a vulnerable system.
RealNetworks Helix Server version 11.x, 12.x, and 13.x
System Compromise: Remote attackers can gain control of vulnerable systems.
Upgrade to the latest version, available from the vendor's web site: