15.4 Security

Notice in the TFTP packets (Figure 15.1) that there is no provision for a username or password. This is a feature (i.e., "security hole") of TFTP. Since TFTP was designed for use during the bootstrap process it could be impossible to provide a username and password.

This feature of TFTP was used by many crackers to obtain copies of a Unix password file and then try to guess passwords. To prevent this type of access, most TFTP servers nowadays provide an option whereby only files in a specific directory (often /tftpboot on Unix systems) can be accessed. This directory then contains only the bootstrap files required by the diskless systems.

For additional security, the TFTP server on a Unix system normally sets its user ID and group ID to values that should not be assigned to any real user . This allows access only to files that have world-read or world-write permissions.