The remote host is missing an update to asterisk announced via advisory DSA 2367-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%202367-1

Several vulnerabilities have been discovered in Asterisk, an Open Source PBX and telephony toolkit: CVE-2011-4597 Ben Williams discovered that it was possible to enumerate SIP user names in some configurations. Please see the upstream advisory for details: http://downloads.asterisk.org/pub/security/AST-2011-013.html This update only modifies the sample sip.conf configuration file. Please see README.Debian for more information on how to update your installation. CVE-2011-4598 Kristijan Vrban discovered that Asterisk can be crashed with malformed SIP packets if the automon feature is enabled. For the oldstable distribution (lenny), this problem has been fixed in version 1:1.4.21.2~dfsg-3+lenny6. For the stable distribution (squeeze), this problem has been fixed in version 1:1.6.2.9-2+squeeze4. For the unstable distribution (sid), this problem has been fixed in version 1:1.8.8.0~dfsg-1. We recommend that you upgrade your asterisk packages.