The remote Debian host is missing a security-related update.
Matthew Nicholson discovered a buffer overflow in the SIP channel driver of Asterisk, an open source PBX and telephony toolkit, which could lead to the execution of arbitrary code.
Upgrade the asterisk packages. For the oldstable distribution (lenny), this problem has been fixed in version 184.108.40.206~dfsg-3+lenny2. For the stable distribution (squeeze), this problem has been fixed in version 220.127.116.11-2+squeeze1.