The lreply function in wu-ftpd 2.6.0 and earlier does not properly cleanse an untrusted format string, which allows remote attackers to execute arbitrary commands via the SITE EXEC command.
https://exchange.xforce.ibmcloud.com/vulnerabilities/4773
http://www.securityfocus.com/bid/1387
http://www.redhat.com/support/errata/RHSA-2000-039.html
http://www.cert.org/advisories/CA-2000-13.html
http://www.calderasystems.com/support/security/advisories/CSSA-2000-020.0.txt
http://marc.info/?l=bugtraq&m=96299933720862&w=2
http://marc.info/?l=bugtraq&m=96179429114160&w=2
http://marc.info/?l=bugtraq&m=96171893218000&w=2
http://archives.neohapsis.com/archives/bugtraq/2000-07/0017.html
http://archives.neohapsis.com/archives/bugtraq/2000-06/0244.html