The remote host is missing an update to libphp-phpmailer announced via advisory DSA 1315-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201315-1

Thor Larholm discovered that libphp-phpmailer, an email transfer class for PHP, performs insufficient input validition if configured to use Sendmail. This allows the execution of arbitrary shell commands. The oldstable distribution (sarge) doesn't include libphp-phpmailer. For the stable distribution (etch) this problem has been fixed in version 1.73-2etch1. For the unstable distribution (sid) this problem has been fixed in version 1.73-4. We recommend that you upgrade your libphp-phpmailer package.