The remote host is missing an update to the system as announced in the referenced advisory FreeBSD-SA-08:03.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-08:03.sendfile.asc
The sendfile(2) system call allows a server application (such as a 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 the Apache HTTP Server and ftpd use sendfile. When a process opens a file (and other file system objects, such as directories), it specifies access flags indicating its intent to read, write, or perform other operations. These flags are checked against file system permissions, and then stored in the resulting file descriptor to validate future operations against. The sendfile(2) system call does not check the file descriptor access flags before sending data from a file.