How Does Egress Filtering Prevent Cyberattacks?

Egress filtering is the practice of monitoring or restricting outgoing data, usually through the use of a firewall that stops packets that do not match particular security standards. The word “egress” means “outgoing,” and an egress router is one that allows packets to exit one network and enter another.

Egress filtering’s major goal is to prevent undesirable or harmful traffic (such as malware, illegal E-mail messages, or requests to Web sites) from leaving a network. A firewall, for example, might be used to prevent students on a university’s campus network from sending viruses or infringing content from any of the machines on the network. Egress filtering can also be utilized in allowing only particular servers or PCs on a company’s network to transfer data outside of it. This safeguard can help prevent employees from using company computers for personal correspondence or casual Web surfing.

Egress filtering is a network security strategy that uses a firewall to filter outgoing data before sending it to another network, preventing all illegal traffic from leaving.

Why Use Egress Filtering?

Outbound or Egress controls protect internal resources from gaining unauthorized access to potentially harmful endpoints on the Internet. Only trusted sites will be accessible through a properly protected VPC, lowering the possibility of your digital services engaging with any unsavory entities and preventing any infections that may have occurred within your servers from phoning home to their command-and-control locations.

Deep-dive into Egress Security & Filtering

Egress filtering limits the amount of data bound to an external entity that passes through the host network’s edge router on its way to its destination node. Before an outbound connection is allowed, a number of policies or filter rulesets must be evaluated; otherwise, a harmful host could be the subject of a request from one of your computers. By allowing only outbound communication over IPv6 from instances in your VPCs to the Internet, Egress-Only Internet Gateways prevent the Internet from creating an IPV6 connection with your instances.

The Egress-only Internet gateway forwards traffic from the subnet’s instances to other AWS services or the Internet, with a response sent back. A single-purpose Internet gateway is built using an amazon VPC console.

Egress filtering can be accomplished using a variety of approaches, including anti-spoofing filters that prevent traffic from leaving the network with faked source addresses, such as those generated by a distributed denial-of-service attack. Because certain services are typically reserved for internal networks and can be linked to exploitation, a filter for internal-only services is required. Filter services that are frequently connected with malicious actions or that should be limited to a small number of recognized hosts.

Egress traffic filtering can assist prevent data exfiltration from network assets because AWS VPCs have NAT gateways but have native AWS IP address limits. Nothing leaves the network without express permission, except those services defined in the egress traffic enforcement policy, thanks to a Deny-All outbound policy, packet filters, or firewall rule.

Through restrictive granular rules, the administrator can gain access to the network and systems. Limiting the addresses that can send data to the Internet by creating an IP spoofing policy that only allows source addresses from the IP network numbers assigned to pass through the firewall in the internal network.

Any network segments or VLANs that have no business connecting to the Internet servers should be disabled. Outbound connections should not be made to destinations listed in the DROP (Don’t route or peer) or BGP filter lists. Only outbound connections from the proxies are allowed via the firewall since the web proxy provides URL and content filtering for HTTP. Blocking routing protocols at the firewall is critical for firewalls that negotiate and exchange PPP over Ethernet.

Best Practices for Egress Filtering

Following are some of the best practices for Egress Filtering −

Use a proxy wherever possible

Your firewalls can only accept traffic from a few proxies rather than the full network if you use proxy breakpoints in the network. This reduces the amount of traffic that reaches the firewall and provides an additional layer of security for your outbound traffic.

Use firewall configuration auditing software

If the firewall isn’t set up for output filtering from the start, the rule set is most likely set up to allow unfiltered outbound traffic. However, because most firewalls have dozens or even tens of thousands of firewall rules, manually scanning them to see which ones are vulnerable is impractical. You can quickly discover risks within the firewall by utilizing a firewall ruleset parser against your firewall rule sets, such as rules enabling outbound at-risk traffic and open ports. Make a mental image of these dangers and assess the systems that utilize them.

Firewall Outbound Rules: Business Justification

Create a policy that states that all future outbound rules must be documented with business reasons, including why these rules were formed, who uses them, which apps and systems use them, and who owns the original business process. This is useful not only for audits but also for understanding your firewall rules, particularly when they enable packets to exit your network.

Examine the Security Zones

Your network most certainly has a DMZ zone, PCI zone, or other sensitive network parts that aren’t accessible directly. These are critical parts of your network, and data entry and exit firewalls require even more attention and control. Their firewalls must be audited on a regular basis and must follow the same logging, reviewing, and controlling protocols as your other firewalls that communicate with external networks.

Balance of security and convenience

Some businesses cannot take the burden of detecting and accepting valid traffic. This is a balance of convenience and security, just like anything else in security. While a default-allow policy is less likely to disrupt regular business operations, it is also less secure.

Egress filtering is difficult to implement, but it is well worth the effort. And it’s possible that it’ll grow more common in the future. Even if it is annoying at times, Egress filtering and even default denial are in the best interests of the organization’s security.