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Can Firewalls Be Hacked? Yes, Here’s 6 Vulnerabilities


Can Firewalls Be Hacked?

Yes, Here’s 6 Vulnerabilities

Like all security tools, firewalls can be hacked. That’s what happened to the social media platform X in January 2023, when it was still Twitter. Hackers exploited an API vulnerability that had been exposed since June the previous year. This gave them access to the platform’s security system and allowed them to leak sensitive information on millions of users.

This breach occurred because the organization’s firewalls were not configured to examine API traffic with enough scrutiny. This failure in firewall protection led to the leak of more than 200 million names, email addresses, and usernames, along with other information, putting victims at risk of identity theft.

Firewalls are your organization’s first line of defense against malware and data breaches. They inspect all traffic traveling into and out of your network, looking for signs of cyber attacks and blocking malicious activity when they find it. This makes them an important part of every organization’s cybersecurity strategy.

Effective firewall management and configuration is vital for preventing cybercrime. Read on to find out how you can protect your organization from attacks that exploit firewall vulnerabilities you may not be aware of.

Understanding the 4 Types of Firewalls

The first thing every executive and IT leader should know is that there are four basic types of firewalls. Each category offers a different level of protection, with simpler solutions costing less than more advanced ones. Most organizations need to use some combination of these four firewall types to protect sensitive data effectively.

Keep in mind that buying more advanced firewalls is not always the answer. Optimal firewall management usually means deploying the right type of firewall for its particular use case. 

Ideally, these should be implemented alongside multi-layered network security solutions that include network detection and response, endpoint security, and security information and event management (SIEM) technology.

1. Packet Filtering Firewalls

These are the oldest and most basic types of firewalls. They operate at the network layer, checking individual data packets for their source IP address and destination IP. They also verify the connection protocol, as well as the source port and destination port against predefined rules. The firewall drops packets that fail to meet these standards, protecting the network from potentially harmful threats.

Packet filtering firewalls are among the fastest and cheapest types of firewalls available. Since they can not inspect the contents of data packets, they offer minimal functionality. They also can’t keep track of established connections or enforce rules that rely on knowledge of network connection states. This is why they are considered stateless firewalls.

2. Stateful Inspection Firewalls

These firewalls also perform packet inspection, but they ingest more information about the traffic they inspect and compare that information against a list of established connections and network states

Stateful inspection firewalls work by creating a table that contains the IP and port data for traffic sources and destinations, and dynamically check whether data packets are part of a verified active connection.

This approach allows stateful inspection firewalls to deny data packets that do not belong to a verified connection. However, the process of checking data packets against the state table consumes system resources and slows down traffic. This makes stateful inspection firewalls vulnerable to Distributed Denial-of-Service (DDoS) attacks.

3. Application Layer Gateways

These firewalls operate at the application layer, inspecting and managing traffic based on specific applications or protocols, providing deep packet inspection and content filtering. They are also known as proxy firewalls because they can be implemented at the application layer through a proxy device.

In practice, this means that an external client trying to access your system has to send a request to the proxy firewall first. The firewall verifies the authenticity of the request and forwards it to an internal server. They can also work the other way around, providing internal users with access to external resources (like public web pages) without exposing the identity or location of the internal device used.

4. Next-Generation Firewalls (NGFW)

Next-generation firewalls combine traditional firewall functions with advanced features such as intrusion prevention, antivirus, and application awareness. They contextualize data packet flows and enrich them with additional data, providing comprehensive security against a wide range of threats.

Instead of relying exclusively on IP addresses and port information, NGFWs can perform identity-based monitoring of individual users, applications, and assets. For example, a properly configured NGFW can follow a single user’s network traffic across multiple devices and operating systems, providing an activity timeline even if the user switches between a desktop computer running Microsoft Windows and an Amazon AWS instance controlling routers and iOT devices.

How Do These Firewalls Function?

Each type of firewall has a unique set of functions that serve to improve the organization’s security posture and prevent hackers from carrying out malicious cyber attacks. Optimizing your firewall fleet means deploying the right type of solution for each particular use case throughout your network. Some of the most valuable functions that firewalls perform include:

Traffic Control

They regulate incoming and outgoing traffic, ensuring that only legitimate and authorized data flows through the network. This is especially helpful in cases where large volumes of automated traffic can slow down routine operations and disrupt operations.

For example, many modern firewalls include rules designed to deny bot traffic. Some non-human traffic is harmless, like the search engine crawlers that determine your website’s ranking against certain keyword searches. 

However, the vast majority of bot traffic is either unnecessary or malicious. Firewalls can help you keep your infrastructure costs down by filtering out connection attempts from automated sources you don’t trust.

Protection Against Cyber Threats

Firewalls act as a shield against various cyber threats, including phishing attacks, malware and ransomware attacks. Since they are your first line of defense, any malicious activity that targets your organization will have to bypass your firewall first.

Hackers know this, which is why they spend a great deal of time and effort finding ways to bypass firewall protection. They can do this by exploiting technical vulnerabilities in your firewall devices or by hiding their activities in legitimate traffic. 

For example, many firewalls do not inspect authenticated connections from trusted users. If cybercriminals learn your login credentials and use your authenticated account to conduct an attack, your firewalls may not notice the malicious activity at all.

Network Segmentation

By defining access rules, firewalls can segment networks into zones with varying levels of trust, limiting lateral movement for attackers. This effectively isolates cybercriminals into the zone they originally infiltrated, and increases the chance they make a mistake and reveal themselves trying to access additional assets throughout your network.

Network segmentation is an important aspect of the Zero Trust framework. Firewalls can help reinforce the Zero Trust approach by inspecting traffic traveling between internal networks and dropping connections that fail to authenticate themselves.

Security Policy Enforcement

Firewalls enforce security policies, ensuring that organizations comply with their security standards and regulatory requirements. Security frameworks like NIST, ISO 27001/27002, and CIS specify policies and controls that organizations need to implement in order to achieve compliance.

Many of these frameworks stipulate firewall controls and features that require organizations to invest in optimizing their deployments. They also include foundational and organizational controls where firewalls play a supporting role, contributing to a stronger multi-layered cybersecurity strategy.

Intrusion Detection and Prevention

Advanced firewalls include intrusion detection and prevention capabilities, which can identify and block suspicious activities in real-time. This allows security teams to automate their response to some of the high-volume security events that would otherwise drag down performance. Automatically detecting and blocking known exploits frees IT staff to spend more time on high-impact strategic work that can boost the organization’s security posture.

Logging and Reporting

Firewalls generate logs and reports that assist in security analysis, incident response, and compliance reporting. These logs provide in-depth data on who accessed the organization’s IT assets, and when the connection occurred. They enable security teams to conduct forensic investigations into security incidents, driving security performance and generating valuable insights into the organization’s real-world security risk profile.

Organizations that want to implement SIEM technology must also connect their firewall devices to the platform and configure them to send log data to their SIEM for centralized analysis. This gives security teams visibility into the entire organization’s attack surface and enables them to adopt a Zero Trust approach to managing log traffic.

Common Vulnerabilities & Weaknesses Firewalls Share

Firewalls are crucial for network security, but they are not immune to vulnerabilities. Common weaknesses most firewall solutions share include:

Zero-day vulnerabilities

These are vulnerabilities in firewall software or hardware that are unknown to the vendor or the general public. Attackers can exploit them before patches or updates are available, making zero-day attacks highly effective. Highly advanced NGFW solutions can protect against zero-day attacks by inspecting behavioral data and using AI-enriched analysis to detect unknown threats.


Backdoors are secret entry points left by developers or attackers within a firewall’s code. These hidden access points can be exploited to bypass security measures. Security teams must continuously verify their firewall configurations to identify the signs of backdoor attacks. Robust and effective change management solutions help prevent backdoors from remaining hidden.

Header manipulation

Attackers may manipulate packet headers to trick firewalls into allowing unauthorized traffic or obscuring their malicious intent. There are multiple ways to manipulate the “Host” header in HTTP traffic to execute attacks. Security teams need to configure their firewalls and servers to validate incoming HTTP traffic and limit exposure to header vulnerabilities.

How Cyber Criminals Exploit These Vulnerabilities

Unauthorized Access

Exploiting a vulnerability can allow cybercriminals to penetrate a network firewall, gaining access to sensitive data, proprietary information, or critical systems. Once hackers gain unauthorized access to a network asset, only a well-segmented network operating on Zero Trust principles can reliably force them to reveal themselves. Otherwise, they will probably remain hidden until they launch an active attack.

Data Breaches

Once inside your network, attackers may exfiltrate sensitive information, including customer data, intellectual property, and financial records (like credit cards), leading to data breaches. These complex security incidents can lead to major business disruptions and reputational damage, as well as enormous recovery costs. 

Malware Distribution

Attackers may use compromised firewalls to distribute malware, ransomware, or malicious payloads to other devices within the network. This type of attack may focus on exploiting your systems and network assets, or it may target networks adjacent to your own – like your third-party vendors, affiliate partners, or customers.

Denial of Service (DDoS)

Exploited firewalls can be used in DDoS attacks, potentially disrupting network services and rendering them unavailable to users. This leads to expensive downtime and reputational damage. Some hackers try to extort their victims directly, demanding organizations pay money to stop the attack.

6 Techniques Used to Bypass Firewalls

1. Malware and Payload Delivery

Attackers use malicious software and payloads to exploit firewall vulnerabilities, allowing them to infiltrate networks or systems undetected. This often occurs due to unpatched security vulnerabilities in popular firewall operating systems. For example, in June 2023 Fortinet addressed a critical-severity FortiOS vulnerability with a security patch. One month later in July, there were still 300,000 Fortinet firewalls still using the unpatched operating system.

2. Phishing Attacks

Phishing involves tricking individuals into divulging sensitive information or executing malicious actions. Attackers use deceptive emails or websites that may bypass firewall filters. If they gain access to privileged user account credentials, they may be able to bypass firewall policies entirely, or even reconfigure firewalls themselves.

3. Social Engineering Tactics

Cybercriminals manipulate human psychology to deceive individuals into disclosing confidential information, effectively bypassing technical security measures like firewalls. This is typically done through social media, email, or by telephone. Attackers may impersonate authority figures both inside and outside the organization and demand access to sensitive assets without going through the appropriate security checks.

4. Deep Packet Inspection Evasion

Attackers employ techniques to disguise malicious traffic, making it appear benign to firewalls using deep packet inspection, allowing it to pass through undetected. Some open-source tools like SymTCP can achieve this by running symbolic executions on the server’s TCP implementation, scanning the resulting execution paths, and sending malicious data through any handling discrepancies identified.

5. VPNs and Remote Access

Attackers may use Virtual Private Networks (VPNs) and remote access methods to circumvent firewall restrictions and gain unauthorized entry into networks. This is particularly easy in cases where simple geo restrictions block traffic from IP addresses associated with certain countries or regions. Attackers may also use more sophisticated versions of this technique to access exposed services that don’t require authentication, like certain containerized servers.

6. Intrusion Prevention Systems (IPS) Bypass

Sophisticated attackers attempt to evade IPS systems by crafting traffic patterns or attacks that go undetected, enabling them to compromise network security. For example, they may use technologies to decode remote access tool executable files hidden inside certificate files, allowing them to reassemble the malicious file after it passes through the IPS.

Protecting Against Firewall Vulnerabilities

Multi-factor Authentication (MFA)

MFA adds an extra layer of security by requiring users to provide multiple forms of identification, such as a password and a one-time code sent to their mobile device, before they gain access. This prevents attackers from accessing sensitive network assets immediately after stealing privileged login credentials. Knowing an account holder’s password and username is not enough.

Two-factor Authentication (2FA)

2FA is a subset of MFA that involves using two authentication factors, typically something the user knows (password) and something the user has (a mobile device or security token), to verify identity and enhance firewall security. Other versions use biometrics like fingerprint scanning to authenticate the user.

Intrusion Prevention Systems (IPS)

IPS solutions work alongside firewalls to actively monitor network traffic for suspicious activity and known attack patterns, helping to block or mitigate threats before they can breach the network. These systems significantly reduce the amount of manual effort that goes into detecting and blocking known malicious attack techniques.

Web Application Firewalls (WAF)

WAFs are specialized firewalls designed to protect web applications from a wide range of threats, including SQL injection, cross-site scripting (XSS), and other web-based attacks. Since these firewalls focus specifically on HTTP traffic, they are a type of application level gateway designed specifically for web applications that interact with users on the public internet.

Antivirus Software and Anti-malware Tools

Deploying up-to-date antivirus and anti-malware software on endpoints, servers, and Wi-Fi network routers helps detect and remove malicious software, reducing the risk of firewall compromise. In order to work effectively, these tools must be configured to detect and mitigate the latest threats alongside the organization’s other security tools and firewalls. Automated solutions can help terminate unauthorized processes before attackers get a chance to deliver malicious payloads.

Regular Updates and Patch Management

Keeping firewalls and all associated software up-to-date with the latest security patches and firmware updates is essential for addressing known vulnerabilities and ensuring optimal security. Security teams should know when configuration changes are taking place, and be equipped to respond quickly when unauthorized changes take place.

Implementing a comprehensive visibility and change management platform like AlgoSec makes this possible. With AlgoSec, you can simulate the effects of network configuration changes and proactively defend against sophisticated threats before attackers have a chance to strike.

Monitoring Network Traffic for Anomalies

Continuous monitoring of network traffic helps identify unusual patterns or behaviors that may indicate a security incident. Anomalies can trigger alerts for further investigation and response. Network detection and response solutions grant visibility into network activities that would otherwise go unnoticed, potentially giving security personnel early warning when unannounced changes or suspicious behaviors take place.

Streamline Your Firewall Security With AlgoSec

Organizations continue to face increasingly sophisticated cyber threats, including attacks that capitalize on misconfigured firewalls – or manipulate firewall configurations directly. Firewall management software has become a valuable tool for maintaining a robust network security posture and ensuring regulatory compliance.

AlgoSec plays a vital role enhancing firewall security by automating policy analysis, optimizing rule sets, streamlining change management, and providing real-time monitoring and visibility. Find out how to make the most of your firewall deployment and detect unauthorized changes to firewall configurations with our help.

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