Authentication is not required to exploit this vulnerability.
The specific flaw exists within the NRouter service while transporting malformed e-mails. The vulnerable code copies data from the ATTACH:CID and Content-ID headers within an e-mail into a fixed length stack buffer. By providing a large enough file name, this buffer can overflow leading to arbitrary code execution under the context of the SYSTEM user.
Disclosure Timeline:
2008-08-26 - Vulnerability reported to vendor
2011-02-07 - Coordinated public release of advisory