The remote host is missing an update to the system as announced in the referenced advisory FreeBSD-SA-05:18.zlib.asc
Upgrade your system to the appropriate stable release or security branch dated after the correction date https://secure1.securityspace.com/smysecure/catid.html?in=FreeBSD-SA-05:18.zlib.asc
zlib is a compression library used by numerous applications to provide data compression/decompression routines. A fixed-size buffer is used in the decompression of data streams. Due to erronous analysis performed when zlib was written, this buffer, which was belived to be sufficiently large to handle any possible input stream, is in fact too small.