How Do Attackers Try to Bypass Firewalls?

Attacks attempt to bypass firewalls by exploiting weaknesses in their design or configuration. Everything from an outdated security policy to a misconfigured or unmonitored port could create an opportunity that an attacker could exploit to breach a firewall. Understanding the common strategies attackers use allows security engineers to strengthen their systems and mitigate threats.

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Firewall Overview

A firewall is an external security layer that monitors incoming and outgoing traffic. Security admins configure firewalls to have specific rules, with only traffic that meets the specifications outlined in these rules being able to move through the barrier. On a large scale, a firewall acts as an external barrier between untrusted or unverified traffic and authorized traffic.

Over time, firewalls expanded to implement other characteristics that improved their threat detection capabilities. For example, next-generation firewalls (NGFWs) also use strategies like malware detection, URL filtering, and application-layer inspection. Some NGFWs even use AI-first strategies to perform contextual threat detection, like detecting unexpected user behavior.

Despite their greater range of technologies, NGFWs, like the original firewalls, still rely on careful configuration by security admins. If the rules that a firewall abides by are misconfigured or don’t accurately cover a certain attack vector, then they may let the threat slip through the gaps.

How Attackers Bypass Firewalls

Attackers focus on finding and exploiting any gaps that security admins leave in firewalls. While not every single attack is due to a misconfiguration, the vast majority stem from small human errors that create an opportunity that hackers then exploit.

Firewalls aren’t inherently flawed, meaning that there aren’t always errors that lead to their compromise. It’s only when firewalls are paired with incorrect or ineffective management that they begin to be the root of potential problems. Considering how common firewalls are, groups of attackers have cultivated a variety of strategies to pinpoint errors and exploit them.

Here are some of the most common strategies and circumstances that allow attackers to bypass firewalls:

Insider Threats: An insider threat is when someone internal to your organization purposefully compromises your security to enable an external attack to occur. Intentional insider threats are rare, although they do happen. Unintentional threats, like someone’s account being hacked, are becoming more common. If someone with a high level of internal privilege gains access, they can disable or reconfigure your firewalls to make an attack easier.
Software Vulnerabilities: Software vulnerabilities in firewalls or any connected systems are much more common than many businesses realize. CISA maintains a public catalog of Known Exploited Vulnerabilities (KEVs), including those that affect firewall products. There’s a major difference between vendors with strong product integrity and those that must continually receive patching due to having critical flaws. Additionally, actively scanning for vulnerabilities in your own firewalls will help identify any potential issues before malicious groups find them.
Lax Firewall Updates: Firewalls receive updates that share information about new threat signatures, improve firmware, or simply issue configuration changes to help better detect and mitigate malicious traffic. These updates typically contain important information that helps firewalls function better. If an organization has routinely skipped updates, its firewalls may be outdated or may even include known vulnerabilities.
Incorrectly Configured Rules: Misconfigurations within firewalls are one of the most common reasons that malicious groups are able to bypass them. Broad policies or even a singular, overly permissive rule can create major issues in a firewall. When groups identify these issues, they can target them to exploit your firewall and bypass its security configurations.
Malware: More traditional firewall solutions focus on detecting potentially malicious behavior at the traffic level. What’s included within the traffic is less important to these systems, creating the potential for malware to bypass the perimeter without raising any red flags. Adaptive malware may even transform its signatures in real time, bypassing inspection and flying under the radar.
DDoS Attacks: DDoS attacks occur when a massive quantity of bot traffic inundates a network, and are another common attack vector to overwhelm firewalls. If a firewall has too much traffic to contend with, it’s unable to effectively inspect data packets in transit. Overloading firewalls with bot traffic can give attackers enough of a window to launch their own smaller attack, slipping it through while the firewall is occupied.
Application-Level Attacks: Application-level attacks focus on Layer 7 of the OSI, completely bypassing a firewall, which operates on network traffic. After moving around the firewall, any malicious payloads that have entered the system can then begin to propagate, potentially even manipulating firewall configurations to make further attacks easier.
Unsecured Remote Access: Remote access attacks occur when malicious groups gain access to authenticated company systems, like a remote employee’s computer. From this authorized device, they can then directly access internal systems, removing the need to bypass the firewall entirely.
Inadequate Inspection Tools: Modern firewalls have a range of additional tools, like DNS filtering and threat detection, that allow them to pinpoint more evasive attack strategies. If a firewall is outdated or doesn’t have these capabilities, it will be much easier to bypass.

Best Practices to Protect Firewalls from Being Bypassed

Many of the main attack vectors that groups use to bypass firewalls stem from poor configurations or oversights by network administrators. With that in mind, mitigating these threats often comes back to doing effective cybersecurity due diligence and making sure everything is configured effectively.

Here are some best practices businesses can follow to help protect their firewalls from common threats:

Audit Firewall Rules and Policies Regularly: Over time, especially when working in an enterprise environment with many security officers, permissions may drift and configurations might no longer align with modern standards. Performing regular audits will help identify places where your policy needs to be tightened, as well as affirm whether or not your firewall configurations are correct. Doing this frequently as a meticulous and central part of your due diligence process will help flag any errors before they cause a vulnerability.
Keep Firewalls Updated: As with any other form of cybersecurity technology, patching to the most recent public edition of a product will ensure that any known vulnerabilities are removed. With firewalls, the most recent update may deliver new and important security protections or simply update configurations to more closely match the industry standards that exist at that moment. Whenever an update is possible, your business should use it to keep your systems as protected as possible. It’s also worth regularly reviewing the CISA KEV Catalog and navigating to the Show Only Security Products view, which will display how different firewall products accumulate known exploited vulnerabilities over time. This can help when assessing the best vendor to opt for and decreasing risk.
Limit Administrative Access: Admin accounts, especially those with all-encompassing permissions, can be extremely dangerous if they fall into the wrong hands. Reducing the number of admin accounts, reducing permission spread, and auditing accounts to close any inactive ones is a good way to reduce the likelihood of an attacker gaining access to a highly-permissioned account.
Apply Traffic Filtering: Traffic filtering is the creation of a strict list of rules that all traffic must meet before being allowed to pass through. By creating highly specific rules, including only allowing specific IP addresses or port numbers to connect, businesses can radically limit the traffic that moves through their network. While this is a limitation on flexibility, it can be customized effectively to prevent malicious traffic.
Educate Staff: Human error, whether it’s falling for a phishing scam or leaving a configuration box unchecked, is the leading cause of breaches. Firewalls are an extremely effective tool that is capable of mounting impressive defenses, but can be useless when misconfigured. Educating staff on the importance of firewall configuration will go a long way toward keeping you safe.
Centralize Firewall Management: Your business is likely contending with numerous firewalls at the same time, deployed across your enterprise and its networks. Instead of managing these separately, a centralized firewall management strategy helps ensure you have a single point of oversight to quickly check and confirm permissions and configurations. Centralizing security management helps reduce risk across the spectrum, eliminating the possibility of forgotten firewalls existing in your network.

Prevent Firewall Evasion with Check Point Network Security and Check Point SASE

Despite being a powerful technology to prevent breaches, firewalls aren’t impenetrable. Especially considering the wide range of tactics that attackers can attempt to employ to bypass firewalls, businesses need to be more aware than ever about how to prevent modern invasion techniques. With these evolving threats, legacy security controls and manual systems aren’t enough to protect firewalls.

Check Point Network Security and Check Point Cloud Firewall deliver industry-leading threat prevention, stopping 99.9% of new malware and advanced attacks before they reach your environment. Powered by real-time AI threat intelligence, Check Point on-premises and cloud firewalls eliminate blind spots that attackers depend on to exploit, fortifying your attack perimeter from the outside in. After scoring #1 in the Miercom Enterprise & Hybrid Mesh Firewall Security report, Check Point is the go-to choice for unparalleled firewall protection.

For businesses that need consistent protection across enterprise environments, Check Point SASE extends its protection across remote users, branch offices, and cloud applications. With Check Point SASE, businesses can protect their users wherever they work, securing their devices without sacrificing performance.

Discover how Check Point’s Next Generation Firewalls protect your network and data from all threats or attacks with a demo.