The remote host is missing an update to the system as announced in the referenced advisory FreeBSD-SA-05:02.sendfile.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-05:02.sendfile.asc

The sendfile(2) system call allows a server application (such as an HTTP or FTP server) to transmit the contents of a file over a network connection without first copying it to application memory. High performance servers such as Apache and ftpd use sendfile. If the file being transmitted is truncated after the transfer has started but before it completes, sendfile(2) will transfer the contents of more or less random portions of kernel memory in lieu of the missing part of the file.