Threats

Security threat assessment is essentially seen by many network administrators and security experts as the primary tool for safeguarding their networks and resources from malicious external attacks. To combat any malicious data packets sent from external sources, they turn to firewalls with tried-and-true monitoring techniques. Yet, security professionals realized that outbound packet filtering is equally as necessary. As a result, they opt for egress filtering to ensure optimal safety and protection.

According to the Allied Market Research report, in 2020, the global firewall-based security market size was US$ 3.48 billion and will reach US$ 24.34 billion by 2030. Egress filtering techniques will account for a large share of this market. Egress filtering is poised to become the newest trend in the market.

This article will walk you through everything you need to know about egress filtering, its application, and some top tips for achieving success.

What is Egress Filtering?

Egress filtering restricts and monitors outgoing data by configuring the firewall before transmitting the data packets to another network. In other words, it filters all data packets leaving your network. Professionals leverage egress filtering techniques in firewalls, Intrusion Prevention Systems (IPS), and packet monitoring systems. 

Effective egress filtering is difficult to enforce, but it is worth the effort. Various industries use this filtering technique to adhere to policy requirements. The best network section where we can implement the egress filter technique is on the network's edge. Every outbound data traffic should pass through the firewall implementing the egress filtering process.

Processes associated with egress filtering

Egress filtering has two main processes. These are:

• Monitoring: It helps record and supervise all outgoing data packets.

• Setting policies and controlling data outflow: Proper configuration and control measure in the egress filter determines which data is authorized to go out and which should be blocked.

Applications of egress filtering

Egress filtering is essential for preventing outbound connections with unsafe and shunned hosts. It might not solve the enterprise's holistic security needs, but in specialized aspects, it can help:

• Block unwanted services: Suppose an enterprise has a policy not to chat on Skype or any other online platform. Security administrators can set an egress filtering technique to block the ports and protocols required to run chatting services. Thus, users cannot use those services as the outgoing traffic gets blocked using the filtering technique.

• Disrupt malware functioning: Suppose your employee's internal machine got infected with malware. In that case, the egress filtering technique can deter the malware from connecting to the command-and-control owner or malware's command server. Again, if spyware tries to export any file to its malicious owner outside the network, the egress filter will stop it from sending it to the destination system.

• Stop machines from becoming malicious: Egress filtering is also an excellent technique to prevent an employee system from becoming a part of a botnet. Egress filtering will block particular types of traffic by preventing enterprise machines from being used as zombie machines for DDoS attacks, spamming, or malware hosting.

• More awareness: Enterprises often have private projects and source codes. Leakage of these projects and source code can lead to massive loss. Therefore, implementing the egress filtering technique will enable security and IT professionals to be alert about private projects going outside the network.

Egress filtering and penetration testing

When performing a penetration test, egress filtering is an important consideration. A penetration test aims to identify vulnerabilities that an attacker could exploit to gain unauthorized access to a network or system. Egress filtering can prevent an attacker from exfiltrating data or communicating with a command and control server once they have gained access to a network.

Penetration testers can use various techniques to test the effectiveness of egress filtering, such as attempting to send data out of the network or establishing a command and control channel to communicate with an external server. By testing the effectiveness of egress filtering, penetration testers can identify any weaknesses in the security controls and make recommendations for improvement.

Best practices while using Egress Firewall

• Use firewall configuration auditing software: Not all firewalls are set up for output filtering from the onset. It allows all outbound traffic without any filter. So, simply implementing the egress filter technique will be useless. Most enterprise-grade firewalls have dozens or thousands of rules and filters implemented. It often becomes confusing. Thus, it is a good practice to use firewall configuration auditing software to check whether the firewall is fit for egress filtering.

• Specific blocking of ports through egress filtering: The SANS Institute is known for its cybersecurity recommendations. It encourages companies to block outbound traffic that uses the following ports:

• Regularly assess or audit security zones: Most enterprise networks contain PCI, demilitarized zones, or other sensitive network zones that require enhanced security. Security engineers can implement egress filtering techniques in those zones and routinely audit those network systems and policies.

  • Trivial File Transfer Protocol (TFTP) - UDP port 69

  • NetBIOS/IP - TCP & UDP ports 137-139

  • MS RPC - TCP & UDP port 135

  • Simple Network Management Protocol (SNMP) - UDP ports 161-162

  • SMB/IP - TCP port 445

  • Internet Relay Chat (IRC) - TCP ports 6660-6669

  • Syslog - UDP port 514

4. Regularly assess or audit security zones: Most enterprise networks contain PCI, demilitarized zones, or other sensitive network zones that require enhanced security. Security engineers can implement egress filtering techniques in those zones and routinely audit those network systems and policies.

Final thoughts

Egress filtering is an important component of network security, and it should be considered during penetration testing to identify vulnerabilities and test the effectiveness of security measures.

Have questions? Contact the Packetlabs team today!