Linux Server Security, Second Edition

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

362

|

Chapter 11: Securing File Services

Anonymous FTP, though, will probably remain with us for some time, so let’s dis-

cuss FTP security, both in general and with specific regard to my preferred FTP serv-

ers, ProFTPD and vsftpd.

Principles of FTP Security

With FTP, we have several major threat models. The first concerns anonymous

access: anonymous users shouldn’t be able to do anything but list and download

public files and maybe upload files to a single “incoming” directory. Needless to say,

we don’t want them to “escalate” their privileges to those of a more trusted user.

Another important FTP threat model involves local user accounts. If a local user logs

in via FTP to upload or download something to or from his home directory, we don’t

want that session hijacked or eavesdropped on by anybody else, or the user’s creden-

tials may be stolen and used with other services such as telnet, SSH, etc.

The third threat model worth considering involves confidentiality. At the very least,

login credentials must be protected from disclosure, as should any other sensitive

data that is transmitted.

Unfortunately, by its very design FTP fails miserably in addressing any but the first of

these threat models: a good FTP server package that is carefully configured can pro-

tect against privilege