This indicates an attack attempt against a Heap Overflow vulnerability in RealNetworks RealPlayer.
The vulnerability is caused by an error when the vulnerable software handles a malformed mp4 file. It allows a remote attacker to execute arbitrary code or crash vulnerable systems via a crafted "mp4" file.
RealPlayer 188.8.131.52 and prior
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.