Ubuntu Manpage: ftp-proxy.conf - configuration file for FTP-Proxy

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NAME

       ftp-proxy.conf - configuration file for FTP-Proxy

SYNOPSIS

       /etc/proxy-suite/ftp-proxy.conf

DESCRIPTION

This manual page documents the configuration file format of the ftp-proxy(8) program. FTP-Proxy is an
application level gateway between FTP clients and servers. Its main purpose is to secure servers against
attacks based on the FTP protocol.

The FTP-Proxy configuration file consists of option lines and comments. A line starting with a '#'
character is a comment. The general format of a option line is

[WhiteSpace] Name WhiteSpace Value [WhiteSpace]

It is recommended to use up to 24 characters for the name and no more than 1024 for the value, although
theoretically both can be up to 4096 in size. Lines can be continued if the last character is a
backslash. The whole file is not case sensitive.

CONTEXT
Option lines always have a context which may be global or user specific. A context is introduced by a
[name] line, where name is the FTP-login name or authuser if the UserAuthMagic feature is used. It is
allowed to use '*' wildcard character at the end of the context name [name*] i.e. [foo*] to match
multiple usernames beginning with "foo". The beginning of the file is implicitly the [-Global-] context
(the dashes allow a user context named [global] without conflict). It is legal to include an option more
than once; the last one will be the one used. Options in user contexts usually take precedence over the
equivalent global option.

Some of the options can be used in a user or the global context, while others make sense only in one of
them. See below.

VARIABLE SUBSTITUTION
Several options (see the individual discussion below for details) support a limited set of variable
substitution when evaluated. The following replacements will be performed:

%b build date of the ftp-proxy(8) program
%d current system date in the form YYYY/MM/DD
%h host name from gethostname(2)
%n network name from getdomainname(2)
%t current system time in the form HH:MM:SS
%v version of the ftp-proxy(8) program
%% a single percent sign

OPTIONS

ActiveMaxDataPort
Both user and global context. Defines the maximum local port number used when connecting to the
client's data port. The latter is either the same as the client's control port or the one given
in the most recent PORT command. If either minimum or maximum value is not given, the program
defaults to using port 20, the ftp-data port as per RFC 959, for the local end of the socket if
the proxy is running as root (user ID 0) or to use a random port. See also ActiveMinDataPort and
User options.

ActiveMinDataPort
Both user and global context. Defines the minimum local port number used when connecting to the
client's data port. See also ActiveMaxDataPort and User options.

AllowMagicUser
Global context only. Defines a flag that when set to yes, true, or on allows the USER name to be
optionally interpreted as user[@host[:port]] where host overrides the DestinationAddress and port
the DestinationPort directive below. It should only be activated with "trusted" users, like in an
outgoing FTP proxy scenario. See also the UserMagicChar and ForceMagicUser options.

AllowTransProxy
Global context only. Defines a flag that when set to yes, true, or on allows one to use the proxy
as transparent proxy for outgoing ftp. To get it working you also have to redirect client
requests on a gateway or firewall host (i.e. via ipchains) to the ftp-proxy. It should only be
activated with "trusted" users, like in an outgoing FTP proxy scenario. You can combine this with
the AllowMagicUser option.

DenyMessage
Global context only. Defines the name of a file which prevents any successful login if it exists,
even if it is empty. The file contents will be sent to the client, each line prefixed with '421-'
and with variable substitution applied. The whole file is followed by a line starting with '421 '
followed by the DenyString below. After sending the connection is closed. If no such file
exists, the deny mechanism is not triggered altogether. See also DenyString option.

DenyString
Global context only. Defines a string that will be displayed to clients, prefixed with '421 ' and
variable substitution applied, if and only if a DenyMessage file exists. The default is 'Service
not available'. See also DenyMessage option.

DestinationAddress
Both user and global context. Defines where to redirect incoming FTP traffic. Can be given as
either dotted decimal IP address or as DNS host name. Please note that the global section must
always contain this option as a basic sanity check.

DestinationMaxPort
Both user and global context. Defines the maximum local port number to be used when opening a
connection to the FTP server. Valid both for control and for data connections. Defaults to not
binding prior to connecting and listening, so that the system selects an arbitrary ephemeral port.
See also DestinationMinPort option.

DestinationMinPort
Both user and global context. Defines the minimum local port number to be used when opening a
connection to the FTP server. See also DestinationMaxPort option.

DestinationPort
Both user and global context. Defines the FTP server's control port where the proxy itself will
connect. This option can either be given as a numeric value or as the service name retrieved by
getservbyname(3) and defaults to port 21, the ftp port as per RFC 959.

DestinationTransferMode
Both user and global context. Defines the FTP transfer mode to be used from the proxy to the
server. Legal values are active, passive, or client. The latter means to follow the mode the
client is using. The default value is client.

FailResetsPasv
Global context only. Defines the action that is taken when a data transfer command is failed on
the server side. If the option is set to yes, true, or on the client data transfer socket will be
closed and the transfer mode set to the default (active-ftp).
If this flag is set to no, false, or off (which is also the default) the socket can be reused for
the next data transfer command in passive mode. This options is a workaround for Netscape (4.x)
clients, that sends a second data transfer command if the first is failed, while the user clicks
on a symbolic link pointing to a directory.
Note, that this behavior may break the RFC definitions.

ForceMagicUser
Global context only. Same as AllowMagicUser, but makes the host and port portion mandatory.

ForkLimit
Global context only. Limits the number of incoming client connections per minute in daemon mode -
it defaults to 40 connections per minute.

Group Global context only. Defines the UNIX style group ID which is set by the process before it serves
clients. Default is to keep the current real group ID.

LDAPAuthDN
Global context only. Defines a different base distinguished name that is used when accessing an
LDAP directory for user authentication purposes. It defaults to the value of LDAPBaseDN. See also
LDAPAuthPWAttr, LDAPAuthPWType, LDAPAuthOKFlag, UserAuthType, LDAPBindDN options.

LDAPAuthOKFlag
Global context only. Defines an attribute and its value as attr=value string, i.e.
userEnabled=yes, that will be checked while user authentication in the directory tree specified
using LDAPAuthDN or LDAPBaseDN. Defaults to an empty string - no flag check used.

LDAPAuthPWAttr
Global context only. Defines the LDAP password attribute name used for user authentication.
A common used attribute name is userPassword. Defaults to an empty string - password
authentication disabled. See also LDAPAuthPWType option.

LDAPAuthPWType
Global context only. Defines the LDAP password type / format and a minimal allowed password
length expected as value for attribute name specified using LDAPAuthPWAttr.

Valid values are plain, crypt, {crypt} followed by one number 0-9, i.e. {crypt}7, plain9 or
plain.

If no minimum length specified the default minimum length of 5 characters is used.

A password type {crypt} means, the password value in the LDAP directory is prefixed by the {crypt}
scheme specification. Other password schemes, i.e. MD5, are not supported at the moment.
Crypted passwords are only available, if the proxy is compiled with crypt support - see also
--with-crypt compile time option in configure script.

If the password (without scheme prefix) stored in LDAP directory is * or ! the account is
disabled and the authentication fails.

Defaults to plain (equivalent to plain5). See also the LDAPAuthOKFlag.

LDAPBaseDN
Global context only. Defines the base distinguished name that is used when accessing an LDAP
directory, i.e. the root of the tree containing the FTP-Proxy entries. Defaults to an empty
string. If UserAuthMagic is used, the authuser is used as user name for authentication and user
profiles, otherwise the normal ftp-user name. See also LDAPIdentifier, LDAPObjectClass,
LDAPServer, UserAuthMagic options.

LDAPBindDN
Defines the distinguished name that is used to (simple) bind the directory service. Defaults to an
empty string (anonymous bind). It is allowed to include one %s in this string, that will be
replaced with the FTP username or authuser if UserAuthMagic is used. See also UserAuthMagic,
LDAPAuthDN, LDAPBindPW options.

LDAPBindPW
Defines the credential (password) that is used to (simple) bind the directory service using
distinguished name given in the LDAPBindDN option. Defaults to an empty string (anonymous bind).

LDAPIdentifier
Global context only. Defines the identification attribute for the access to the LDAP directory.
This can be thought of as the primary key and defaults to the string CN which is short for "Common
Name." See also LDAPBaseDN, LDAPObjectClass, LDAPServer options.

LDAPObjectClass
Global context only. Defines the LDAP object class which holds the entries for the FTP-Proxy
access control. It is assumed that the possible user specific config options exist as attributes
within a record of this type. There is no default, but a value of FTPProxyUser is recommended.
See also LDAPBaseDN, LDAPIdentifier, LDAPServer options.

LDAPServer
Global context only. This is the main option for using an LDAP directory for retrieving user
specific values. If given, it denotes the server (and possible port separated by a colon) where
FTP-Proxy will ask for the attributes. The program will bind as the anonymous user and try to
retrieve the values from the tree rooted at LDAPBaseDN, having an object class of LDAPObjectClass
and identified by the LDAPIdentifier. If the server cannot be reached, the program aborts. If
the user cannot be found, the program falls back to the configuration file, but will query only
the global values and not the user specific ones. See also LDAPBaseDN, LDAPBindDN,
LDAPIdentifier, LDAPObjectClass options.

LDAPVersion
Global context only. Use this option to set the LDAP API version, the proxy should set: 2 or 3.
Use 0 to skip explicit version setting and use library defaults. Defaults is version 3 if
supported by the library or 2 if not.
Note: OpenLDAP 2.x library defaults to version 2 bind, but the OpenLDAP server refuses LDAPv2 bind
by default.

Listen Global context only. Defines the address where the proxy itself opens the listening port. The
default is 0.0.0.0 which instructs the server to bind to any address. See also Port option.

LogDestination
Global context only. Defines the destination of the logging information the program wishes to
emit. If the value starts with a slash (/) it will be interpreted as an absolute path. This file
will be created and kept open during the lifetime of the process. The signal SIGUSR1 can be sent
to the (daemon) process in order to rotate this log file.

A second way to provide logging is via a pipe and is employed when the first character of the
option is a pipe symbol (|). In this case the rest of the value is interpreted as the name of a
UNIX command which is invoked and receives logging information on its standard input.

The third way is to use the syslog(3) service which is assumed for all other values. The option
value is interpreted as the syslog facility while the severity is defined by the various messages
themselves.

LogLevel
Global context only. Defines the maximal level of logged messages. The levels are, in order of
decreasing importance: FLT, ERR, WRN, INF, DBG
The default level is INF. A LogLevel set to WRN causes, that only messages with levels FLT, ERR,
WRN will be logged.

MaxClients
Global context only. Defines the maximum number of clients the proxy will allow concurrently.
The valid range for this option is 1 to 512, with a default of 64. See also MaxClientsMessage,
MaxClientsString options.

MaxClientsMessage
Global context only. Defines the name of a file that is displayed to clients if their maximum
number defined with MaxClients has been exceeded. If no such file exists only the MaxClientsString
is displayed, else both the file and the string are transmitted. After transmission the
connection is terminated in any case. When sending the file, each line is prefixed with '421-'
and variable substitution is applied to it. See also MaxClients, MaxClientsString options.

MaxClientsString
Global context only. Defines a string that will be displayed to clients, prefixed with '421 ' and
variable substitution applied, if the maximum client number has been exceeded. The default is
'Service not available' . See also MaxClients, MaxClientsMessage options.

MaxRecvBufSize
Global context only. Defines the maximum number of bytes read from socket at once while data
transfers. Default is to read all data as reported by the kernel.
It may be useful to set a limit (i.e. to 8192), if your proxy machine uses two interfaces of
different speed, i.e. the clients are accessing the proxy via a high-speed interface (i.e. Fast-
Ethernet) and the proxy is accessing servers using a slower one (i.e. modem, ISDN link) and your
ftp-clients aborts the data transfers because of a timeout.

PassiveMaxDataPort
Both user and global context. Defines the maximum local port number used when listening for the
client's data connection. This is the port number transmitted to the client in a 227 response to
the PASV command. If either minimum or maximum value is not given, the program defaults to let
the system choose an arbitrary ephemeral port. See also PassiveMinDataPort option.

PassiveMinDataPort
Both user and global context. Defines the minimum local port number used when listening for the
client's data connection. See also PassiveMaxDataPort option.

PidFile
Global context only. Defines the name of a process ID file where FTP-Proxy will store its process
ID if running as daemon. The file contents will be an ASCII string with a trailing newline. On
many operating systems such PID files will be located in the /var/run directory.

Port Global context only. Defines the listening port where the FTP-Proxy offers its service. The port
can be given as a number or as a string suitable for retrieval by the getservbyname(3) function.
It defaults to port 21, the ftp port as per RFC 959. See also Listen option.

PortResetsPasv
Global context only. Defines the action that is taken when a PORT command is received while a
passive port is open for listening. If the option is set to yes, true, or on, (which is also the
default) the socket will be closed and the passive mode will be terminated (set to active-ftp).
Setting the option to no, false, or off does not cancel the listen. This flag seems necessary
because the RFC is not really clear enough about the correct handling.

SameAddress
Both user and global context. Defines a boolean value which determines if the proxy is allowed to
be included in so-called third party server to server transfers. In this situation the client
first sends a PASV command to one server, then a PORT command with the response code to the second
server, and then initiates the transfer with mutual transfer commands on the two servers.
Specifying this option as no, false, or off allows FTP-Proxy to take part in such a transfer,
while saying yes, true, or on (the default) will enforce that transfers can only take place
to/from the client itself.

ServerRoot
Defines the directory into which the FTP-Proxy performs a chroot(2) in order to increase its
security level. See also the User and Group options.

Note, that you have to copy needed libraries, configuration files, etc into this directory first!

ServerType
Global context only. Defines the mode in which the FTP-Proxy is running if no command line switch
(-d/-i) has been provided. The option value can either be inetd in which case the proxy expects
the client to be available at standard input and output, or it can be standalone which means the
process will become a daemon, open the listening port and fork child processes for all future
connections. The child processes themselves will behave exactly as if they were started from
inetd.

SockBindRand
Global context only. Defines a flag that when set to yes, true, or on , causes the proxy to use a
random port in the specified range via DestinationMinPort/MaxPort, ActiveMinPort/MaxDataPort,
PassiveMinDataPort/MaxDataPort instead of increment the port number inside of this range. See also
DestinationMinPort, DestinationMaxPort, PassiveMinDataPort, PassiveMaxDataPort, ActiveMinPort,
ActiveMaxPort options.

TCPWrapper
Global context only. Defines a boolean value which is evaluated by the FTP-Proxy running as a
standalone daemon only. Saying yes, true, or on activate the TCP Wrapper library, whereas no,
false, or off (the default) disable the function. See also TCPWrapperName option.

TCPWrapperName
Global context only. Use given name for TCP-Wrapper checks instead of the program name (argv[0]).
See also TCPWrapper option.

TimeOut
Both user and global context. Defines the time in seconds after which a client is assumed to be
disconnected. If no activity is detected from the client after this time, the connection is
closed and the process terminates. Default value is 900 seconds.

TranslatedAddress
Global context only. Defines an IP address the server will use in 227 replies to PASV commands
instead of its own address. Usually the address where the client connected to is taken, but this
may not be appropriate in situations where an NAT (Network Address Translation) device is located
in the way from the client to the proxy. In this situation the response can be changed to include
the input address of the NAT device.

The value for this option can be given as a DNS host name, as a dotted decimal IP address, or as a
file name. The latter is assumed when the name starts with a slash. The file is opened and
scanned for the desired address. Blank lines or lines starting with '#' are ignored. Reading the
address from a file may be useful for environments with masquerading and dynamic PPP connections.

User Global context only. Defines the UNIX style user ID which is given to the process before it
serves clients. Default is to keep the current real user ID.

If the proxy does not run as a privileged user (root, user ID 0), it has no permission to bind a
socket to port < 1024 or to preform a chroot(2) call. See also ActiveMinDataPort,
ActiveMaxDataPort, ServerRoot options.

UserMagicChar or UseMagicChar
Global context only. Defines the character to use as separator between user and host[:port] in the
target setting of AllowMagicUser Default is the '@' character. This allows you to use E-Mail
addresses as usernames for login to the ftp server (i.e. me@mydomain%ftp.server:21 if you set it
to %).

UserAuthMagic
Global context only. This is an authentication extension like AllowMagicUser, allowing encoding of
additional username and password in the USER and PASS commands for authentication. Valid values
are @auth for ftpuser@authuser[@host:port] and ftppass@authpass or auth@ for
authuser@[ftpuser@host:port] and authpass@ftppass. See also LDAPBindDN, LDAPAuthType and
AllowMagicUser.

UserAuthType
Global context only. Defines the authentication mechanism the proxy should use. Currently "ldap"
is implemented to support simple LDAP authentication using FTP username and password from USER and
PASS commands or the special authuser and authpass encoded using UserAuthMagic. See also
LDAPBindDN, LDAPAuthDN, LDAPAuthPWAttr, LDAPAuthPWType, LDAPAuthOKFlag and UserAuthMagic options.

UserNameRule
Global context only. Defines a regular expression rule for validation of the user name (used for
profile-setup and authentication purposes). Defaults to:

^[[:alnum:]]+([%20@/\._-][[:alnum:]]+)*$

It checks, if the first character is alphanumeric, optionally followed by @/_-. or alphanumeric
characters and ending with an alphanumeric one.

This matches the usual cases inclusive E-Mail addresses and "domain/user" names.

If regex support is not available, above default rule is still used and the option ignored. See
also ValidCommands option for regex encoding description.

ValidCommands
Both user and global context. Defines the list of allowed FTP commands for the client. If this
option is not installed, there will be no restriction on the allowed commands. But if it is
given, then all commands not on this list will be denied. The list is space separated and may
consist of the following commands: USER, PASS, ACCT, CWD, CDUP, SMNT, QUIT, REIN, PORT, PASV,
TYPE, STRU, MODE, RETR, STOR, STOU, APPE, ALLO, REST, RNFR, RNTO, ABOR, DELE, RMD, MKD, PWD, LIST,
NLST, SITE, SYST, STAT, HELP, NOOP, SIZE, MDTM, MLFL, MAIL, MSND, MSOM, MSAM, MRSQ, MRCP, XCWD,
XMKD, XRMD, XPWD, XCUP, AUTH, APSV, EPRT, and EPSV.

Each command can be followed by an optional equals sign and POSIX 1003.2 Extended Regular
Expression (RE) that describes the valid argument(s) for the command. If the whole string is to
be matched, the pattern has to start with a caret (^) and end with a dollar ($). If no pattern
follows a command, its arguments are not checked. An example for a name would be the pattern
'^[a-zA-Z0-9]{1,512}$' for an argument that is mandatory and may consist of up to 512 letters or
digits only. A command that does not allow any arguments can also easily be represented:
'QUIT=^$' .

Please note that the regular expression is "pre-processed". This means that a pattern in the form
%xx will be interpreted as a hexadecimal constant and will be replaced by the value of that
constant. This looks a bit like HTML and helps to include characters that might not be handled as
expected, like %20 for space or %5c (equivalent to %5C) for backslash. The space is especially
important because it is the separator for the commands within the list itself.

Please note also that regular expression support must have been enabled with the --with-regex
switch during the configure compilation step of the whole package.

WelcomeMessage
Global context only. Defines the name of a file that will be displayed to all clients as the
first action when they open the control connection. Each line is prefixed with '220-' and
variable substitution is applied to it. If no such file exists it is silently ignored. See also
WelcomeString option.

WelcomeString
Global context only. Defines the string that is sent to the client in order to start login
negotiation. The string is prefixed with '220 ' and variable substitution is applied to it. If
this option is not given it defaults to the following string:
'%h FTP server (%v - %b) ready'.
See also WelcomeMessage option.

FILES

       /etc/proxy-suite/ftp-proxy.conf
       /usr/sbin/ftp-proxy

AUTHORS

       Jens-Gero Boehm <jens-gero.boehm@suse.de>
       Pieter Hollants <pieter.hollants@suse.de>
       Volker Wiegand <volker.wiegand@suse.de>
       Marius Tomaschewski <mt@suse.de>

COPYRIGHT

       The SuSE Proxy-Suite is released under the
       GNU General Public License (GPL).