The remote host is missing an update to syslog-ng announced via advisory DSA 175-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%20175-1

Péter Höltzl discovered a problem in the way syslog-ng handles macro expansion. When a macro is expanded a static length buffer is used accompanied by a counter. However, when constant chharacters are appended, the counter is not updated properly, leading to incorrect boundary checking. An attacker may be able to use specially crafted log messages inserted via UDP which overflows the buffer. This problem has been fixed in version 1.5.15-1.1 for the current stable distribution (woody), in version 1.4.0rc3-3.2 for the old stable distribution (potato) and version 1.5.21-1 for the unstable distribution (sid). We recommend that you upgrade your syslog-ng package immediately.