source: http://www.securityfocus.com/bid/17641/info

Asterisk Recording Interface is prone to an information-disclosure vulnerability. This issue is due to a failure in the application to properly sanitize user-supplied input. 

An attacker can exploit this vulnerability to retrieve arbitrary MP3, WAV, and GSM files from the vulnerable system in the context of the application. Attackers may also exploit this issue to determine the existence of arbitrary files that don't have MP3, WAV, or GSM filename extensions.

Information gained by exploiting this issue may aid malicious users in further attacks.

http://www.example.com/recordings/misc/audio.php?recording=/var/spool/asterisk/voicemail/default/<mailbox>/INBOX/msg<messageid>.wav