This indicates an attack attempt to exploit a remote File Inclusion vulnerability in Microsoft Rich TextBox.
The vulnerability, which is located in the "RICHTX32.OCX" ActiveX control, can be exploited through misuse of a vulnerable method "SaveFile". An attacker can exploit this by tricking an unsuspecting user into visiting a malicious webpage and can overwrite or create arbitrary file within the context of the application.
Microsoft Rich TextBox Control 6.0
System Compromise: Remote attackers can gain control of vulnerable systems.
Currently we are unaware of any vendor supplied patch or updates available for this issue.