4369 - Pentesting Erlang Port Mapper Daemon (epmd)

👉 Overview

👀 What ?

The Erlang Port Mapper Daemon (epmd) is a small name server included in Erlang/OTP and used by Erlang nodes to locate each other on a network. It maps symbolic node names to machine addresses, allowing distributed Erlang systems to communicate. In the context of cybersecurity, pentesting (penetration testing) epmd refers to the process of probing this server for vulnerabilities that can be exploited.

🧐 Why ?

The importance of pentesting epmd lies in its role as a potential entry point for attacks. An insecure epmd can be exploited by attackers to gain unauthorized access to a distributed Erlang system, causing serious security breaches. Therefore, it's important for cybersecurity professionals to understand how to pentest epmd, identify vulnerabilities, and propose solutions to secure it.

⛏️ How ?

Pentesting epmd involves several steps. First, you need to identify the target system running epmd. This can be done using network scanning tools like nmap. Once you've identified the target, you can proceed to probe it for vulnerabilities. This could involve testing for weak or default credentials, lack of encryption, or unauthenticated access. Finally, after identifying possible weaknesses, you should propose and implement solutions to secure the epmd.

⏳ When ?

Pentesting epmd should be carried out regularly as a part of an organization's overall cybersecurity strategy. It's particularly important when setting up a new distributed Erlang system or making significant changes to an existing one.

⚙️ Technical Explanations

Erlang Port Mapper Daemon (epmd) is a crucial component of the Erlang Open Telecom Platform (OTP) that functions as a name server for Erlang nodes, mapping symbolic node names to machine addresses. This mapping allows distributed Erlang systems on a network to locate and communicate with each other effectively.

When an Erlang node wants to connect with another node, it queries epmd to fetch the TCP port associated with the node's symbolic name. The node then uses this port information to establish a connection with the desired node.

Epmd maintains a local database containing (name, port) pairs. Each pair consists of a symbolic node name and a TCP port on which the corresponding Erlang node is listening. This database is the key resource that facilitates the connection between Erlang nodes in a distributed system.

Despite its important role, by default, epmd does not implement any form of authentication or encryption. This lack of security measures means any entity that can connect to the epmd can register or unregister node names or query the node list. Since epmd listens on all network interfaces by default, this poses a significant security risk.

In the cybersecurity context, penetration testing (pentesting) epmd involves probing this server for potential vulnerabilities. The pentesting process generally involves identifying the target system running epmd (using network scanning tools like nmap), probing the identified target for vulnerabilities (like weak or default credentials, lack of encryption, or unauthenticated access), and then proposing and implementing solutions to secure the epmd.

Regularly pentesting epmd and securing it is crucial for maintaining the security of a distributed Erlang system. This is particularly important when establishing a new distributed Erlang system or when making significant updates to an existing one. Ensuring that epmd is secure helps prevent unauthorized access and potential security breaches in the distributed Erlang system.

Here's an illustrative example of how to perform a basic pentest of an Erlang Port Mapper Daemon (epmd) using nmap.

1. Identify the target system: The first step in pentesting is to identify the target system running epmd. A network scanning tool like nmap can be used for this. The following command scans the network for hosts running epmd on the default port (4369):

   nmap -p 4369 <target-ip-range>
   
   

2. Probe for vulnerabilities: After identifying the target, we probe it for vulnerabilities. One common vulnerability is that epmd does not implement any form of authentication or encryption by default. To check this, you can try to register a node name with epmd using the following command:

   erl -name mynode@localhost
   
   

   If the node is registered without any form of authentication, this indicates a vulnerability.

3. Propose and implement solutions: After identifying possible weaknesses, you should propose and implement solutions to secure the epmd. One possible solution is to restrict access to the epmd to only trusted IP addresses. This can be done by modifying the epmd configuration file and adding a firewall rule:

   iptables -A INPUT -p tcp --dport 4369 -s <trusted-ip-address> -j ACCEPT
   iptables -A INPUT -p tcp --dport 4369 -j DROP
   
   

   This will only allow connections to epmd from the trusted IP address and drop all other connection attempts.

Remember, this is a simplified example for illustrative purposes and real-world pentesting involves additional steps and considerations.