The remote host is missing an update to php-json-ext announced via advisory DSA 1775-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201775-1

It was discovered that php-json-ext, a JSON serialiser for PHP, is prone to a denial of service attack, when receiving a malformed string via the json_decode function. For the oldstable distribution (etch), this problem has been fixed in version 1.2.1-3.2+etch1. The stable distribution (lenny) does not contain a separate php-json-ext package, but includes it in the php5 packages, which will be fixed soon. The testing distribution (squeeze) and the unstable distribution (sid) do not contain a separate php-json-ext package, but include it in the php5 packages. We recommend that you upgrade your php-json-ext packages.