acFTP is an open-source FTP daemon for Windows platforms
(http://www.sourceforge.net/projects/acftp) that offers more functionality
than many proprietary servers (including the MS FTP service). The
authentication code of acFTP contains a flaw -- specifically, the server
treats users as logged in without a valid password. This results in
mis-representation of server activity in log files, and possibly privilege
elevation.

For example:

USER private
PASS #

This leads it to reject my password, but I can not log in with another set
of credentials, and my log activity appears as "private" instead of the
appropriate "-" or "***".

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