The remote Debian host is missing a security-related update.
Several vulnerabilities were discovered in Asterisk, a PBX and telephony toolkit. - CVE-2012-2947 The IAX2 channel driver allows remote attackers to cause a denial of service (daemon crash) by placing a call on hold (when a certain mohinterpret setting is enabled). - CVE-2012-2948 The Skinny channel driver allows remote authenticated users to cause a denial of service (NULL pointer dereference and daemon crash) by closing a connection in off-hook mode. In addition, it was discovered that Asterisk does not set the alwaysauthreject option by default in the SIP channel driver. This allows remote attackers to observe a difference in response behavior and check for the presence of account names. (CVE-2011-2666 ) System administrators concerned by this user enumerating vulnerability should enable the alwaysauthreject option in the configuration. We do not plan to change the default setting in the stable version (Asterisk 1.6) in order to preserve backwards compatibility.
Upgrade the asterisk packages. For the stable distribution (squeeze), this problem has been fixed in version 1:220.127.116.11-2+squeeze6.