Securing ejabberd
Firewall Settings
You need to take the following TCP ports in mind when configuring your firewall:
| Port | Description |
|---|---|
| 5222 | Standard port for Jabber/XMPP client connections, plain or STARTTLS. |
| 5223 | Standard port for Jabber client connections using the old SSL method. |
| 5269 | Standard port for Jabber/XMPP server connections. |
| 4369 | EPMD (see epmd) listens for Erlang node name requests. |
| port range | Used for connections between Erlang nodes. This range is configurable (see epmd). |
epmd
epmd (Erlang Port Mapper Daemon)
is a small name server included in Erlang/OTP and used by Erlang
programs when establishing distributed Erlang communications. ejabberd
needs epmd to use ejabberdctl and also when clustering ejabberd
nodes. This small program is automatically started by Erlang, and is
never stopped. If ejabberd is stopped, and there aren't any other
Erlang programs running in the system, you can safely stop epmd if you
want.
ejabberd runs inside an Erlang node. To communicate with ejabberd,
the script ejabberdctl starts a new Erlang node and connects to the
Erlang node that holds ejabberd. In order for this communication to
work, epmd must be running and listening for name requests in the port
4369. You should block the port 4369 in the firewall in such a way that
only the programs in your machine can access it, or configure the option
ERL_EPMD_ADDRESS in the file ejabberdctl.cfg.
If you build a cluster of several ejabberd instances, each ejabberd
instance is called an ejabberd node. Those ejabberd nodes use a
special Erlang communication method to build the cluster, and EPMD is
again needed listening in the port 4369. So, if you plan to build a
cluster of ejabberd nodes you must open the port 4369 for the machines
involved in the cluster. Remember to block the port so Internet doesn't
have access to it.
Once an Erlang node solved the node name of another Erlang node using
EPMD and port 4369, the nodes communicate directly. The ports used in
this case by default are random, but can be configured in the file
ejabberdctl.cfg. The Erlang command-line parameter used internally is,
for example:
erl ... -kernel inet_dist_listen_min 4370 inet_dist_listen_max 4375
It is also possible to configure in ejabberdctl.cfg the network
interface where the Erlang node will listen and accept connections. The
Erlang command-line parameter used internally is, for example:
erl ... -kernel inet_dist_use_interface "{127,0,0,1}"
Erlang Cookie
The Erlang cookie is a string with numbers and letters. An Erlang node
reads the cookie at startup from the command-line parameter
-setcookie. If not indicated, the cookie is read from the file
$HOME/.erlang.cookie.
If this file does not exist, it is created
immediately with a random cookie in the user $HOME path.
This means the user running ejabberd must have a $HOME,
and have write access to that path.
So, when you create a new account in your system for running ejabberd,
either allow it to have a $HOME,
or set as $HOME a path where ejabberd will have write access.
Depending on your setup, examples could be:
adduser --home /usr/local/var/lib/ejabberd ejabberd
or
adduser --home /var/lib/ejabberd ejabberd
Two Erlang nodes communicate only if they have the same cookie. Setting a cookie on the Erlang node allows you to structure your Erlang network and define which nodes are allowed to connect to which.
Thanks to Erlang cookies, you can prevent access to the Erlang node by mistake, for example when there are several Erlang nodes running different programs in the same machine.
Setting a secret cookie is a simple method to difficult unauthorized access to your Erlang node. However, the cookie system is not ultimately effective to prevent unauthorized access or intrusion to an Erlang node. The communication between Erlang nodes are not encrypted, so the cookie could be read sniffing the traffic on the network. The recommended way to secure the Erlang node is to block the port 4369.
Erlang Node Name
An Erlang node may have a node name. The name can be short (if indicated
with the command-line parameter -sname) or long (if indicated with the
parameter -name). Starting an Erlang node with -sname limits the
communication between Erlang nodes to the LAN.
Using the option -sname instead of -name is a simple method to
difficult unauthorized access to your Erlang node. However, it is not
ultimately effective to prevent access to the Erlang node, because it
may be possible to fake the fact that you are on another network using a
modified version of Erlang epmd. The recommended way to secure the
Erlang node is to block the port 4369.
Securing Sensitive Files
ejabberd stores sensitive data in the file system either in plain text
or binary files. The file system permissions should be set to only allow
the proper user to read, write and execute those files and directories.
ejabberd configuration file: /etc/ejabberd/ejabberd.yml: Contains the JID of administrators and passwords of external
components. The backup files probably contain also this information,
so it is preferable to secure the whole /etc/ejabberd/ directory.
ejabberd service log: /var/log/ejabberd/ejabberd.log: Contains IP addresses of clients. If the loglevel is set to 5, it
contains whole conversations and passwords. If a logrotate system is
used, there may be several log files with similar information, so it
is preferable to secure the whole /var/log/ejabberd/ directory.
Mnesia database spool files in /var/lib/ejabberd/: The files store binary data, but some parts are still readable. The
files are generated by Mnesia and their permissions cannot be set
directly, so it is preferable to secure the whole
/var/lib/ejabberd/ directory.
Erlang cookie file: /var/lib/ejabberd/.erlang.cookie: See section Erlang Cookie.
