The remote host is missing an update to wzdftpd announced via advisory DSA 1006-1. kcope discovered that the wzdftpd FTP server lacks input sanitising for the SITE command, which may lead to the execution of arbitrary shell commands. The old stable distribution (woody) does not contain wzdftpd packages.
For the stable distribution (sarge) this problem has been fixed in version 0.5.2-1.1sarge1. For the unstable distribution (sid) this problem has been fixed in version 0.5.5-1. We recommend that you upgrade your wzdftpd package. https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201006-1