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 cookie file $HOME/.erlang.cookie. If this file does not exist, it is created immediately with a random cookie. 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.