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<h2><b>ProFTPD module <code>mod_auth</code></b></h2>
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<hr><br>
This module is contained in the <code>mod_auth.c</code> file for
ProFTPD 1.3.<i>x</i>, and is compiled by default.
<h2>Directives</h2>
<ul>
<li><a href="#AllowChrootSymlinks">AllowChrootSymlinks</a>
<li><a href="#AnonRequirePassword">AnonRequirePassword</a>
<li><a href="#AuthAliasOnly">AuthAliasOnly</a>
<li><a href="#AuthUsingAlias">AuthUsingAlias</a>
<li><a href="#CreateHome">CreateHome</a>
<li><a href="#DefaultRoot">DefaultRoot</a>
<li><a href="#MaxLoginAttempts">MaxLoginAttempts</a>
<li><a href="#RequireValidShell">RequireValidShell</a>
<li><a href="#RewriteHome">RewriteHome</a>
<li><a href="#RootLogin">RootLogin</a>
<li><a href="#RootRevoke">RootRevoke</a>
<li><a href="#TimeoutLogin">TimeoutLogin</a>
<li><a href="#TimeoutSession">TimeoutSession</a>
<li><a href="#UseFtpUsers">UseFtpUsers</a>
<li><a href="#UserAlias">UserAlias</a>
<li><a href="#UserPassword">UserPassword</a>
</ul>
<hr>
<h2><a name="AllowChrootSymlinks">AllowChrootSymlinks</a></h2>
<strong>Syntax:</strong> AllowChrootSymlinks <em>on|off</em><br>
<strong>Default:</strong> AllowChrootSymlinks on<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_auth<br>
<strong>Compatibility:</strong> 1.3.5rc1 and later
<p>
The <code>AllowChrootSymlinks</code> directive configures whether
<code>proftpd</code> will follow a symlink to the destination directory
when performing a <code>chroot(2)</code> call. This applies both to
<a href="#DefaultRoot"><code>DefaultRoot</code></a> directives <b>and</b> to
<code><Anonymous></code> sections.
<p>
<b>Security note</b>: If you permit your users the ability to remove
directories which might be FTP users' home directories (<i>or</i>
<code><Anonymous></code> directories) and create symlinks, then you
<b>should</b> use:
<pre>
AllowChrootSymlinks off
</pre>
This includes sites which are hosting providers, <i>i.e.</i> which allow
users to run their untrusted webapps (<i>e.g.</i> PHP, Perl, Ruby, Python,
<i>etc</i> apps) on the servers.
<p>
<hr>
<h2><a name="AnonRequirePassword">AnonRequirePassword</a></h2>
<strong>Syntax:</strong> AnonRequirePassword <em>off|on</em><br>
<strong>Default:</strong> AnonRequirePassword off<br>
<strong>Context:</strong> <code><Anonymous></code><br>
<strong>Module:</strong> mod_auth<br>
<strong>Compatibility:</strong> 0.99.0 and later
<p>
Normally, anonymous FTP logins do not require the client to authenticate
themselves using <em>real</em> passwords; instead, anonymous FTP logins are
expected to provide their email address as the password. Using
<code>AnonRequirePassword on</code>, however, will <i>require</i> a real
password for that login. The provided password will be matched against the
<code><Anonymous></code> user's password.
<p>
This functionality, in conjunction with the <code>AuthUsingAlias</code>
directive, can be used to create "guest" accounts, which function exactly as
normal anonymous logins do, <b>but</b> which require a valid password on the
server's host system.
<p>
See also: <a href="#AuthUsingAlias"><code>AuthUsingAlias</code></a>, <a href="#UserAlias"><code>UserAlias</code></a>
<p>
<hr>
<h2><a name="AuthAliasOnly">AuthAliasOnly</a></h2>
<strong>Syntax:</strong> AuthAliasOnly <em>off|on</em><br>
<strong>Default:</strong> AuthAliasOnly off<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_auth<br>
<strong>Compatibility:</strong> 1.1.3 and later
<p>
The <code>AuthAliasOnly</code> directive restricts authentication to "aliased"
logins only, <i>i.e.</i> those usernames provided by clients which are "mapped"
to a <em>real</em> username by the <code>UserAlias</code> directive. Using
<code>AuthAliasOnly on</code> in a particular configuration context will
cause ProFTPD to completely ignore all <em>non-aliased</em> logins for the
entire context.
<p>
See also: <a href="#AuthUsingAlias"><code>AuthUsingAlias</code></a>, <a href="#UserAlias"><code>UserAlias</code></a>
<p>
<hr>
<h2><a name="AuthUsingAlias">AuthUsingAlias</a></h2>
<strong>Syntax:</strong> AuthUsingAlias <em>off|on</em><br>
<strong>Default:</strong> AuthUsingAlias off<br>
<strong>Context:</strong> <code><Anonymous></code><br>
<strong>Module:</strong> mod_auth<br>
<strong>Compatibility:</strong> 1.2.0pre9 and later
<p>
The <code>AuthUsingAlias</code> directive disables the resolving of aliased usernames (via <code>UserAlias</code>) for authentication purposes. For example,
if you have aliased the username "anonymous" to the real user "ftp", the
password gets checked against the user "anonymous". When
<code>AuthUsingAlias</code> is <em>disabled</em>, the checked username would
be "ftp".
<p>
Here is an example of an <code><Anonymous></code> section where only
the aliased usernames are allowed to login:
<pre>
<Anonymous ~ftp>
AuthUsingAlias on
UserAlias anonymous nobody
UserAlias ftp nobody
# Make this a read-only anonymous login
<Limit WRITE>
DenyAll
</Limit>
</Anonymous>
</pre>
and here, by contrast, is an <code><Anonymous></code> section where
certain real users are allowed to login <i>using their own passwords</i> (even
though it will still be considered an <i>anonymous</i> login):
<pre>
<Anonymous ~ftp>
# Require real passwords for these logins
AnonRequirePassword on
AuthAliasOnly on
AuthUsingAlias on
# This is the list of authorized users; password checks will occur
# using their own respective passwords, not user "nobody".
UserAlias fred nobody
UserAlias jenn nobody
</Anonymous>
</pre>
<p>
See also: <a href="#AnonRequirePassword"><code>AnonRequirePassword</code></a>, <a href="#UserAlias"><code>UserAlias</code></a>
<p>
<hr>
<h2><a name="CreateHome">CreateHome</a></h2>
<strong>Syntax:</strong> CreateHome <em>off|on [mode] [skel path] [dirmode mode]</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_auth<br>
<strong>Compatibility:</strong> 1.2.8rc2 and later
<p>
The <code>CreateHome</code> directive configures the server to automatically
create a user's home directory, if that directory does not exist, during the
login process.
<p>
The <em>mode</em> parameter is used to configure the absolute mode of the home
directory created. If not specified, the mode will default to 700.
<p>
The optional <em>skel path</em> parameters can be used to configure an
<code>/etc/skel</code>-like directory containing account initialization files
and directories. The parameter must be the full path to the skeleton directory.
The directory must <b>not</b> be world-writeable. Files copied from this
directory into the new home directory will have ownership set to the UID and
GID of the logging-in user. Note that sockets and FIFOs in the skeleton
directory will <b>not</b> be copied; any setuid or setgid bits on files will be
removed from the copied files in the target home directory.
<p>
The optional <em>dirmode</em> parameter can be used to specify the mode for
intermediate directories that may need to be created in order to create the
target home directory. By default, the mode for such intermediate directories
will be 711. <b>Note</b>: using a mode that does not include the execute bit to
be enabled can cause havoc. <b><i>You have been warned.</i></b>
<p>
Examples:
<pre>
# Use the CreateHome default settings
CreateHome on
# Specify a skeleton directory
CreateHome on skel /etc/ftpd/skel
# No skeleton, but make sure that intermediate directories have 755
# permissions.
CreateHome on dirmode 755
# Skeleton directory, with 700 intermediate directories
CreateHome on skel /etc/ftpd/skel dirmode 700
</pre>
<p>
A fuller description of the <code>CreateHome</code> directive and its uses,
with more examples, can be read <a href="../howto/CreateHome.html">here</a>.
<p>
<hr>
<h2><a name="DefaultRoot">DefaultRoot</a></h2>
<strong>Syntax:</strong> DefaultRoot <em>path [group-expression]</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_auth<br>
<strong>Compatibility:</strong> 1.2.0rc1
<p>
The <code>DefaultRoot</code> directive is used to <code>chroot()</code> the
session process for the connecting client. A fuller explanation can be
found in the <a href="../howto/Chroot.html">Chroot</a> howto.
<p>
<hr>
<h2><a name="MaxLoginAttempts">MaxLoginAttempts</a></h2>
<strong>Syntax:</strong> MaxLoginAttempts <em>count</em><br>
<strong>Default:</strong> 3<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_auth<br>
<strong>Compatibility:</strong> 0.99.0 and later
<p>
The <code>MaxLoginAttempts</code> directive configures the maximum number of
times a client may attempt to authenticate to the server <i>on the same TCP
connection</i>. After the number of attempts exceeds the configured
<em>count</em>, the client is disconnected and an appropriate message is
logged.
<p>
<hr>
<h2><a name="RequireValidShell">RequireValidShell</a></h2>
<strong>Syntax:</strong> RequireValidShell <em>on|off</em><br>
<strong>Default:</strong> RequireValidShell on<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code>, <code><Anonymous></code><br>
<strong>Module:</strong> mod_auth<br>
<strong>Compatibility:</strong> 0.99.0 and later
<p>
The <code>RequireValidShell</code> directive configures the server, virtual
host or anonymous login to allow or deny logins which do not have a shell
listed in <code>/etc/shells</code>. By default, <code>proftpd</code>
<b>will not allow a login</b> unless the user's default shell is listed in
<code>/etc/shells</code>. If <code>/etc/shells</code> cannot be found, all
default shells are assumed to be valid.
<p>
<hr>
<h2><a name="RewriteHome">RewriteHome</a></h2>
<strong>Syntax:</strong> RewriteHome <em>on|off</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code>
<strong>Module:</strong> mod_auth<br>
<strong>Compatibility:</strong> 1.3.3rc1 and later
<p>
The <code>RewriteHome</code> directive can be used to support rewriting the
home directory for a user, based on regular expression rules. One such use
case is where some portion of the home directory is retrieved <i>e.g.</i>
from an LDAP directory, but you need to apply some custom prefix to the LDAP
attribute. <b>Note</b> that this feature requires that the
<code>mod_rewrite</code> module also be present in your <code>proftpd</code>
daemon.
<p>
To enable this feature, first you need to add the following to your
<code>proftpd.conf</code>:
<pre>
RewriteHome on
</pre>
Next, you need to configure the mod_rewrite rules for rewriting your home
directory; this feature depends on the <code>mod_rewrite</code> module for the
rewriting. The pseudo-command used by <code>mod_rewrite</code> for rewriting
home directories is "REWRITE_HOME". Thus would you use:
<pre>
<IfModule mod_rewrite.c>
RewriteEngine on
RewrlteLog /path/to/rewrite.log
RewriteCondition %m REWRITE_HOME
RewriteRule (.*) /my/new/prefix$1
</IfModule>
</pre>
<p>
<hr>
<h2><a name="RootLogin">RootLogin</a></h2>
<strong>Syntax:</strong> RootLogin <em>on|off</em><br>
<strong>Default:</strong> RootLogin off<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code>, <code><Anonymous></code><br>
<strong>Module:</strong> mod_auth<br>
<strong>Compatibility:</strong> 1.1.5 and later
<p>
Normally, <code>proftpd</code> does <b>not allow</b> root logins under any
circumstance. If a client attempts to login as root, using the correct
password, a special security message is logged:
<pre>
SECURITY VIOLATION: root login attempted.
</pre>
When <code>RootLogin on</code> is used, the root user may authenticate just as
any other user could (assuming no <i>other</i> access control measures deny
access); however the root login security message is still logged:
<pre>
ROOT FTP login successful.
</pre>
Obviously, extreme care should be taken when using this directive.
<p>
The use of <code>RootLogin</code> in the <code><Anonymous></code>
context is only valid when the <code>User</code>/<code>Group</code> defined
in the <code><Anonymous></code> section is set to 'root'.
<p>
<hr>
<h2><a name="RootRevoke">RootRevoke</a></h2>
<strong>Syntax:</strong> RootRevoke <em>on|off|UseNonCompliantActiveTransfers</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code>, <code><Anonymous></code><br>
<strong>Module:</strong> mod_auth<br>
<strong>Compatibility:</strong> 1.2.9rc1 and later
<p>
The <code>RootRevoke</code> directive causes all root privileges to be dropped
once a user is authenticated. This will also cause active data transfers
(<i>e.g.</i> via the <code>PORT</code>/<code>EPRT</code> FTP commands) to be
disabled <i>if the server is listening on a port less than 1024</i>. Note that
this only affects <i>active</i> data transfers; passive transfers will not be
blocked.
<p>
The reason for rejecting active data transfers in these cases is because of
a requirement in RFC 959 (which defines the File Transfer Protocol) that for
active data transfers, the data connection <b>must</b> have a source port of
<em>L</em>-1, where <em>L</em> is the control connection port (see RFC 959, Section 3.2 "Establishing Data Connections"). Thus if the FTP server listens on
port 21, then a client requesting an active data transfer from that server
will have a data connection whose source port (on the server) is port 20
(<em>L</em> = 21, <em>L</em>-1 = 20).
<p>
Even though passive data transfers are highly preferable, many FTP clients
may still require/expect to be able to do an active data transfer. One
question, though, is how many FTP clients actually <i>check</i> that the
source port of the active data transfer connection is actually <em>L</em>-1.
Or how many networking appliances along the way (<i>i.e.</i> firewalls, NATs,
routers, <i>etc</i>) enforce this restriction as well.
<p>
If not for that requirement, then with "RootRevoke on" in the
<code>proftpd.conf</code>, <code>proftpd</code> would not be <i>required</i>
to use root privileges for binding to a privileged port like port 20.
<p>
Thus the <code>RootRevoke</code> directive also accepts (as of <code>proftpd-1.3.5rc1</code>) a parameter of "UseNonCompliantActiveTransfers", <i>e.g.</i>:
<pre>
# Drop root privs, but allow active data tranfers (only use a non-standard
# source port for the active data connection).
RootRevoke UseNonCompliantActiveTranfers
</pre>
With this configuration, <code>proftpd</code> will drop root privileges,
<i>but</i> would <b>not</b> reject <code>PORT</code>/<code>EPRT</code>
commands at all. Instead, the active data transfers would be allowed as per
normal, except that <code>proftpd</code> would not try to bind to the
<em>L</em>-1 port for those active transfers.
<p>
This <code>RootRevoke</code> parameter is valuable because it helps in
getting <code>proftpd</code> to drop root privileges for sessions more often,
which is a <b>far more secure configuration</b>. Exploits such as the
"Roaring Beast" attack would not be possible in a session where root privileges
have been dropped completely.
<p>
<hr>
<h2><a name="TimeoutLogin">TimeoutLogin</a></h2>
<strong>Syntax:</strong> TimeoutLogin <em>seconds</em><br>
<strong>Default:</strong> 300 seconds<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_auth<br>
<strong>Compatibility:</strong> 0.99.0 and later
<p>
The <code>TimeoutLogin</code> directive configures the maximum number of
<em>seconds</em> a client is allowed to spend authenticating, <i>i.e.</i>
from the time when the client connects to the time when the client has
successfully authenticated. The login timer is <b>not</b> reset when a client
transmits data, and is only removed once a client has transmitted an
acceptable combination of <code>USER</code>/<code>PASS</code> commands.
The maximum allowed <em>seconds</em> value is 65535 (108 minutes).
<p>
See also: <a href="mod_core.html#TimeoutIdle"><code>TimeoutIdle</code></a>,
<a href="mod_xfer.html#TimeoutNoTransfer"><code>TimeoutNoTransfer</code></a>,
<a href="mod_xfer.html#TimeoutStalled"><code>TimeoutStalled</code></a>
<p>
<hr>
<h2><a name="TimeoutSession">TimeoutSession</a></h2>
<strong>Syntax:</strong> TimeoutSessions <em>seconds</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code>, <code><Anonymous></code><br>
<strong>Module:</strong> mod_auth<br>
<strong>Compatibility:</strong> 1.2.6rc1 and later
<p>
The <code>TimeoutSession</code> directive sets the maximum number of
<em>seconds</em> a control connection between the proftpd server and client
can exist, after the client has successfully authenticated. If the
<em>seconds</em> argument is set to zero, sessions are allowed to last
indefinitely; this is the default. There is no maxium value for the
<em>seconds</em> parameter.
<p>
<hr>
<h2><a name="UseFtpUsers">UseFtpUsers</a></h2>
<strong>Syntax:</strong> UseFtpUsers <em>on|off</em><br>
<strong>Default:</strong> UseFtpUsers on<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code>, <code><Anonymous></code><br>
<strong>Module:</strong> mod_auth<br>
<strong>Compatibility:</strong> 0.99.0 and later
<p>
Legacy FTP servers generally check a special authorization file (typically
<code>/etc/ftpusers</code>) when a client attempts to authenticate.
<b>If</b> the user's name is <i>found</i> in this file, FTP access is
<i>denied</i>. For compatibility of behavior, <code>proftpd</code> defaults to
checking this same file during authentication. This behavior can be suppressed
using the <code>UseFtpUsers</code> directive, <i>e.g.</i>:
<pre>
# Do not check /etc/ftpusers
UseFtpUsers off
</pre>
<p>
<hr>
<h2><a name="UserAlias">UserAlias</a></h2>
<strong>Syntax:</strong> UserAlias <em>alias real-user</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code>, <code><Anonymous></code><br>
<strong>Module:</strong> mod_auth<br>
<strong>Compatibility:</strong> 0.99.0 and later
<p>
ProFTPD requires a real username (<i>i.e.</i> known via
<code>/etc/passwd</code>, <code>AuthUserFile</code>, LDAP, SQL, RADIUS,
<i>etc</i>) when authenticating a client. There <i>are</i>, however, times
when an additional <em>alias</em> is required <i>but</i> is undesirable to
provide an additional login accounts.
<p>
The <code>UserAlias</code> directive provides a mechanism to do just this.
A typical and common example of <code>UserAlias</code> is for
<code><Anonymous></code> configuration sections. It is conventional for
the server to use user "ftp" as the primary authentication user; it is common
practice to allow users to login using the name "anonymous". This is achieved
by using the following in the config file:
<pre>
<Anonymous ~ftp>
...
UserAlias anonymous ftp
...
</Anonymous>
</pre>
<p>
<hr>
<h2><a name="UserPassword">UserPassword</a></h2>
<strong>Syntax:</strong> UserPassword <em>user encrypted-password</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code>, <code><Anonymous></code><br>
<strong>Module:</strong> mod_auth<br>
<strong>Compatibility:</strong> 0.99.0pl5 and later
<p>
The <code>UserPassword</code> directive creates a password for a particular
<em>user</em>; this configured password will <i>override</i> the user's normal
password in <code>/etc/passwd</code> (or whichever auth module handles that
user). <b>Note</b> that the <em>user</em> configured is a real user, and
<b>not</b> a <code>UserAlias</code>.
<p>
The <em>encrypted-password</em> parameter is a string which has been passed
through the standard Unix <code>crypt(3)</code> function. <b>Do not use a
cleartext password</b>. To obtain this <em>encrypted-password</em> value,
you can use the <a href="../utils/ftpasswd.html"><code>ftpasswd</code></a>
script's <code>--hash</code> option, <i>e.g.</i>:
<pre>
# ftpasswd --hash
Password:
Re-type password:
ftpasswd: $1$EsnXxyD6$tsO2YwTAT/Tl5u1NYPHIw1
</pre>
<p>
Example configuration:
<pre>
# Override user bob's password with a hash version of "password"
UserPassword bob $1$EsnXxyD6$tsO2YwTAT/Tl5u1NYPHIw1
</pre>
<p>
<hr>
<h2><a name="Installation">Installation</a></h2>
The <code>mod_auth</code> module is compiled by default.
<p>
<hr>
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