3632 - Pentesting distcc

👉 Overview

👀 What ?

Pentesting distcc, or Distributed C Compiler, involves the process of testing the security of a network or system that utilizes distcc. Distcc is a program designed to distribute compilations of C, C++, Objective C, or Objective C++ code across multiple machines in a network.

🧐 Why ?

Pentesting distcc is crucial because misconfigurations or security vulnerabilities in distcc can allow unauthorized access to a system, leading to potential data breaches or system damage. Understanding how to properly test distcc's security can help identify and patch vulnerabilities, protecting the system and the data it holds.

⛏️ How ?

To carry out a pentest on distcc, one must first identify the nodes in the network running distcc. Scanning tools like Nmap can be used for this purpose. Once identified, the tester can attempt to exploit known vulnerabilities or misconfigurations in the distcc setup. After the test, all found vulnerabilities should be properly patched and the system hardened to prevent future attacks.

⏳ When ?

Pentesting distcc should be done periodically and especially after any changes to the network or system configuration. It is also recommended to conduct a pentest after installing or updating distcc to ensure no new vulnerabilities have been introduced.

⚙️ Technical Explanations

Pentesting distcc involves a comprehensive analysis of the security measures implemented within a system utilizing the Distributed C Compiler (distcc). The process takes advantage of the inherent nature of distcc, which is its distribution of tasks across a network. This distributed nature, while beneficial for task efficiency, can introduce several vulnerabilities if not properly secured.

One of the most common vulnerabilities of distcc is its lack of authentication by default. This means that any individual with knowledge of the distcc server can connect to it and execute arbitrary commands. An attacker can exploit this vulnerability to gain unauthorized access to the system, which could lead to severe consequences such as data breaches or system damage.

The pentesting process begins with the identification of nodes in the network running distcc. This can be achieved using scanning tools like Nmap. Once these nodes are identified, the pentester can exploit known vulnerabilities or misconfigurations within the distcc setup. This may involve attempting to connect to the distcc server and execute commands, thereby testing the system's vulnerability to unauthorized access.

After the pentesting process, all discovered vulnerabilities should be appropriately addressed to harden the system against future attacks. This could include implementing an allow list of IP addresses that can access the distcc server, enabling authentication requirements for connecting to the server, and utilizing a firewall for additional protection.

An important point to note is that pentesting distcc should be done periodically, especially after any changes to the network or system configuration. It is also recommended to conduct a pentest after installing or updating distcc to ensure no new vulnerabilities have been introduced. This proactive approach of regular testing allows for the timely identification and resolution of security issues, thereby maintaining the integrity and security of the system.

Let's imagine a scenario where we are pentesting a system utilizing distcc. We begin by identifying nodes in the network running distcc using Nmap, a popular network scanning tool:

nmap -p 3632 [target IP range]

This command will scan the target IP range for port 3632, which is typically used by distcc. The output will list all IPs where port 3632 is open, indicating potential distcc servers.

Next, we attempt to connect to a detected distcc server using netcat (nc):

nc [distcc server IP] 3632

If we're able to connect, it means the server might not be properly secured. To verify, we can try executing a simple command:

echo "void main() { }" | nc [distcc server IP] 3632

If the server processes this arbitrary C code, it confirms the lack of authentication and command execution vulnerability.

After identifying these vulnerabilities, we need to address them. The sysadmin can implement an IP allow list for the distcc server. This is typically done in the distcc configuration file:

ALLOWED_HOSTS="[allow list IP range]"

Next, enable authentication on the distcc server. This can be done by setting up a distcc user and password, and configuring the server to require these credentials.

Finally, a firewall can be set up for additional protection. Using iptables, we can restrict access to port 3632:

iptables -A INPUT -p tcp --dport 3632 -j DROP
iptables -A INPUT -p tcp -s [allow list IP range] --dport 3632 -j ACCEPT

This blocks all incoming traffic to port 3632, except from IPs within the allow list.

Remember, pentesting distcc should be done periodically, especially after system changes or updates. This proactive approach helps maintain the system's security.