The remote host is missing an update to the system as announced in the referenced advisory FreeBSD-SA-06:21.gzip.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-06:21.gzip.asc
gzip is a file compression utility. Multiple programming errors have been found in gzip which can be triggered when gzip is decompressing files. These errors include insufficient bounds checks in buffer use, a NULL pointer dereference, and a potential infinite loop.