The dataconn function in ftpd.c in netkit ftpd (netkit-ftpd) 0.17, when certain modifications to support SSL have been introduced, calls fclose on an uninitialized file stream, which allows remote attackers to cause a denial of service (daemon crash) and possibly have unspecified other impact via some types of FTP over SSL protocol behavior, as demonstrated by breaking a passive FTP DATA connection in a way that triggers an error in the server's SSL_accept function. NOTE: the netkit ftp issue...

More... (http://nvd.nist.gov/nvd.cfm?cvename=CVE-2007-6263)