Just a week following the release of MS05-021, proof of concept exploit code was published by FrSIRT, the French Security Incident Response Team. This demonstrates code that could serve as a basis for the development of a Remote Code Execution Exploit.

This code clearly means that if anyone failed to apply the fix by now, must do so immediately. See references for details.

References

Critical and Moderate Exchange Updates

Microsoft Exchange Server Remote Code Execution Exploit (MS05-021)