How firewalls protect against ransomware attacks

Updated: April 3, 2026
Author: Sophos

As attackers increasingly target exposed services, identities, and unmonitored network paths, the firewall becomes one of the few control points positioned to detect and disrupt activity early, before adversaries reach high‑value systems. This guide explains how modern firewalls help prevent cyberattacks, the gaps they close, and how organizations should configure them for maximum ransomware resilience.

How can firewalls help secure networks against ransomware?

Cyber threats don’t keep office hours, and neither should your defenses. With most ransomware attacks beginning outside normal business hours, businesses need protection that does not rely on someone being at their desk to respond.

Ransomware remains one of the most disruptive threats facing organizations today. The Sophos State of Ransomware 2025 report found that the average ransom demand dropped below $2 million in 2024 to $1.3 million in 2025.

To defend against ransomware, organizations need to harden their networks, inspect traffic thoroughly and be prepared to detect and respond to intrusions. 

How ransomware attacks work and how to respond

Understanding how attackers operate is the first step toward stopping them. A typical ransomware attack begins with initial access through vulnerable web applications or misconfigured or unpatched edge devices, then progresses through:

• Persistence
• Lateral movement
• Discovery of valuable systems
• Encryption and data exfiltration

Attackers exploit implicit trust in remote access tools and unpatched vulnerabilities to move deeper into the environment. Once inside, they quietly explore the network, looking for paths to sensitive data. The longer they remain undetected, the higher the cost of recovery.
Even organizations with regular patch cycles face zero-day exposure windows. Attackers rapidly weaponize newly disclosed vulnerabilities, creating repeated opportunities for compromise.
As ransomware attacks become more pervasive, organizations need to step up their defenses and dramatically reduce their risk by following best practices:

1. Deploy a hardened firewall: Deploy a Sophos Firewall, then apply hardening guidelines for firmware updates, service access, authentication, access rules, protections, and notifications.
2. Reduce your attack surface: Opportunistic exploitation is ongoing, not one‑and‑done. Consolidate devices, patch firmware, secure services. Identify and remove end-of-life (EOL) or unsupported devices that no longer receive security updates, as they create persistent entry points for attackers. Enforce strong authentication and replace VPNs with zero-trust network access (ZTNA) policies.
3. Inspect and protect all traffic: Decrypt and inspect encrypted flows, enable IPS and zero‑day protection, and deploy robust email security with user training.
4. Detect and respond quickly: Attackers exploit the vulnerability window — the time between when a vulnerability is exposed (including zero-day and unpatched known flaws) and when it is remediated. Segment networks, leverage integrated network detection and response (NDR), extended detection and response (XDR), and/or managed detection and response (MDR) solutions, and automate incident response through synchronized security.

Why firewalls matter in ransomware defense

Network layer controls play a critical role in stopping attackers early in the attack chain. Modern firewalls provide visibility, inspection, and segmentation that limit attackers’ ability to gain traction, even if they compromise a user account or endpoint. Firewalls with IPS, geo-blocking, and strict access control policies reduce openings and disrupt automated scanning and exploitation. Firewalls help secure networks against ransomware by:

1. Strengthening the network perimeter

Most ransomware attacks still begin at the edge through exposed services, weak credentials, and unpatched or unsupported systems. 

A firewall serves as the first line of defense against ransomware, inspecting traffic, blocking malicious connections, and enforcing security policies. Sophos Firewall provides this protection while also integrating with other defenses to create a unified security ecosystem.

Key firewall capabilities:

• Blocks malicious traffic, phishing payloads, and command-and-control (C2) communications.
• Performs deep TLS inspection to uncover threats in encrypted traffic.
• Prevents lateral movement through Active Threat Response and coordinating firewalls, endpoints, switches, and access points to isolate compromised devices.
• Offers automated hardening, applying best-practice configurations for authentication and intrusion prevention.

Explore more firewall features

2. Reducing your attack surface

Once attackers gain a foothold, their success depends on how much freedom your network architecture gives them. 

An effective ransomware defense starts with limiting the exposure of critical systems and services.

• Consolidate network infrastructure: Multiple gateways and VPNs increase the attack surface. Reduce the number of public‑facing devices and upgrade to a firewall that integrates remote access and, ideally, ZTNA. 
• Replace remote‑access VPN with ZTNA: ZTNA eliminates the implicit trust of legacy VPNs by verifying user identity and device health before granting access. It micro‑segments applications and automatically cuts off compromised devices.
  
  Sophos Firewall includes integrated ZTNA, providing a single gateway for remote access. 
• Patch and update firmware: Unpatched vulnerabilities were the leading cause of ransomware attacks in 2024. Schedule regular firmware updates during maintenance windows to keep systems current and leverage high-availability (HA) deployments to minimize disruption. At the same time, ensure automatic hotfixes are enabled (the default setting), so critical security fixes can be applied over the air as soon as they are released, without requiring downtime.
• Secure by Design: Choose network devices designed for security. Recommended features include no default internet access, granular access controls, multi‑factor authentication (MFA), and hardened portals.
  Sophos Firewall is engineered to be secure by design and features proactive monitoring and automatic hotfixes.
• Minimize exposed services: Reduce or eliminate services exposed to the internet. Review NAT and firewall rules to ensure remote‑access services are not accidentally exposed.
  
  Sophos recommends disabling user portal access on the WAN, using ZTNA for remote administration, and avoiding direct NAT access for Internet of Things (IoT) devices.
• Strong authentication: Enforce strong passwords and MFA across all accounts. Block repeated failed login attempts and use CAPTCHAs to prevent brute‑force attacks. Role‑based access controls limit exposure if credentials are compromised.
  
  Ransomware actors exploit stolen credentials and weak identity controls. Sophos Identity Threat Detection and Response (ITDR) extends protection beyond devices to user accounts. Sophos ITDR monitors logins, detects privilege abuse, and correlates identity events with network and endpoint activity.
  
  Learn more about Sophos ITDR
  
  Tip: By linking/integrating ITDR with MDR and Firewall telemetry, organizations can automatically detect and isolate identity-driven attacks.
• Micro‑segment the network: Create small network zones or VLANs and connect them through a firewall to apply anti‑malware and intrusion‑prevention inspection between segments. Micro‑segmentation limits lateral movement and allows early detection of intruders.

3. Inspecting and protecting network traffic

Much of today’s network traffic is encrypted, and attackers hide within it. Sophos’ whitepaper “Best practices for securing your network from ransomware” notes that more than 90% of network traffic is encrypted, creating a blind spot for traditional security tools. Organizations must inspect this traffic without sacrificing performance. 

• Decrypt and inspect encrypted traffic: Organizations should decrypt and inspect encrypted traffic to uncover threats hidden in TLS sessions.
  
  How Sophos helps: Sophos Firewall’s Xstream TLS engine automatically determines which flows require decryption and enforces strong encryption policies without degrading performance while maintaining visibility into encrypted traffic and securing access to management, user, and VPN portals with modern cryptographic protections.
• Enable intrusion prevention (IPS): Apply IPS on all traffic flows, not just internet‑bound connections. Many organizations neglect IPS, leaving unpatched systems vulnerable. Sophos Firewall includes next‑generation IPS and streaming deep packet inspection powered by machine learning analysis.
• Use zero‑day threat protection: Traditional signature‑based scanning cannot detect bespoke ransomware. Leverage AI‑powered threat scanning and real‑time sandboxing to identify unknown malware.
  
  How Sophos helps: Sophos Firewall integrates AI and machine learning technologies trained on millions of samples and performs real‑time cloud sandbox analysis.
• Implement email security and user training: Phishing remains a prevalent entry point. Use email security solutions that filter malicious messages, rewrite URLs for time‑of‑click checks, and provide phishing‑awareness training for users.
  
  How Sophos helps: Sophos Email uses AI‑powered natural‑language processing to detect impersonation and rewrites URLs for time‑of‑click inspection.
• Near real-time web category alerting: This is especially valuable for education institutions and organizations that need rapid visibility into high-risk browsing behavior to support compliance and keep users safe online.
  
  How Sophos helps: Sophos Firewall v22 introduces near real-time alerting for restricted and inappropriate web categories, with notifications delivered as frequently as every five minutes.

4. Detecting and stopping threats inside the network

Given the sophistication of adversaries, assume that an attacker will eventually breach the perimeter. Rapid detection and automated response reduce dwell time and limit damage.

• Segment the network and monitor internal traffic: Use VLANs with managed switches and access points to create granular security zones, and route traffic between segments through the firewall for inspection and policy enforcement.
  
  How Sophos helps: Sophos recommends micro‑segmenting applications with ZTNA to prevent ransomware propagation.
• Identify adversaries quickly: 88% of ransomware attacks occur outside regular business hours, making 24/7 monitoring essential. Choose a security stack that shares threat intelligence across products and can automatically isolate compromised hosts.
  
  How Sophos helps: Sophos Firewall also employs advanced intrusion prevention, AI-based zero-day detection, and deep packet inspection to identify and block emerging ransomware campaigns in real time.
• Automate response: Speed is critical once an attacker breaches the perimeter. When a threat is detected, the firewall and endpoints should automatically detect and contain it.
  
  How Sophos helps: Sophos Firewall’s Active Threat Response coordinates with endpoints, switches, and access points to isolate compromised devices. This synchronized response prevents lateral movement and cuts off malicious communications.
• Remote integrity monitoring: Sophos’ security teams continuously monitor telemetry, accelerating investigation and response if an attack targets the firewall itself. This capability strengthens a critical layer of defense as adversaries increasingly attempt to compromise security appliances.
  
  How Sophos helps: Sophos Firewall v22 integrates a Sophos XDR Linux sensor directly into the OS, enabling real-time monitoring of system integrity. The sensor detects unauthorized configuration changes, file tampering, suspicious process activity, and unexpected rule exports — blind spots traditionally invisible to firewalls. 
• Use network detection and response (NDR): NDR analyzes metadata from TLS‑encrypted traffic and DNS queries to detect anomalous patterns.
  
  How Sophos helps: Sophos Firewall v21.5 integrated NDR Essentials — an industry-first — which uses AI to analyze encrypted payloads without decryption. Detections are scored and returned to the firewall via the threat‑feed API, allowing administrators to set risk thresholds for alerts. This integration provides faster, deeper insights into active adversaries and reduces response time from days to minutes.
• Leverage MDR: For many organizations, relying solely on in‑house security teams is impractical. Sophos MDR provides 24/7 threat hunting and incident response delivered by experts. The whitepaper “Best practices for securing your network from ransomware" recommends implementing MDR services to rapidly neutralize attacks that technology alone cannot stop.
  
  Tip: Sophos MDR provides continuous threat hunting and expert-led response to contain attacks before encryption begins.

Firewall hardening best practices

Steps to harden firewall configurations, which complement the general best practices above:

1. Limit device service access: Disable non‑essential services on the WAN interface, such as SSH or HTTPS admin portals. Manage devices through Sophos Central.
2. Use strong passwords, MFA and role‑based access: Enforce MFA, strong passwords, and role‑based access controls.
3. Minimize access to internal systems: Audit NAT and firewall rules to ensure no unnecessary WAN‑to‑LAN access and avoid exposing IoT devices directly.
4. Enable appropriate protection: Apply IPS inspection to incoming untrusted traffic, enable DoS/DDoS protections, and block traffic from regions where you do not conduct business.
5. Enable alerts and notifications: Configure email or SNMP notifications for system events and ensure logs are sent to Sophos Central or your SIEM.
6. Keep firmware up to date: Regularly update firewall firmware and automate hotfixes to minimize disruption.

Why Sophos?
Because “Secure by Design” firewall hardening matters

Firewalls are built to protect your network, but they must also be protected.
Attackers aren’t just targeting users or endpoints anymore. They increasingly probe network infrastructure for weak points, and a misconfigured or unmaintained firewall can create a direct path to unauthorized access, ransomware deployment, or full‑scale network compromise.

That’s why Secure by Design principles are so important. A firewall should reduce risk from the moment it’s deployed, not rely on extensive manual hardening or after‑the‑fact tuning to be safe.

What's in a Secure by Design firewall

Next‑generation firewalls move beyond performance specs and feature lists. The real indicator of long-term protection is how the product is architected, updated, and continuously validated.

Key security foundations include:

• No default internet exposure for administrative services: Preventing external access to management interfaces dramatically reduces the attack surface.
• Hardened system architecture with strict access controls: Built‑in least privilege and compartmentalized services limit what an attacker can reach if something goes wrong.
• Automatic security updates and rapid patching capabilities: Firewalls must be able to receive and apply critical fixes quickly to shrink the window of exposure.
• Proactive monitoring and integrity checks: Early detection of tampering or abnormal behavior is essential to stopping attacks before they escalate.
• Ongoing configuration validation against best practices: Continuous assessment helps ensure strong security hygiene over time — especially in dynamic environments.

A properly hardened Secure by Design firewall strengthens your overall security posture and ensures that the device protecting your network doesn’t become a risk itself.

Recognition and innovation

Sophos Firewall has received independent recognition for its effectiveness. In G2’s Spring 2025, Fall 2025, Winter 2026, and Spring 2026 reports, Sophos Firewall was ranked the #1 overall firewall.

In June 2025, we launched NDR Essentials integrated with Sophos Firewall. This industry‑first integration offloads AI‑driven traffic analysis to the cloud, allowing detection of malicious encrypted payloads without TLS decryption. By scoring detections and feeding them back to the firewall’s threat feed, the system enables administrators to set alert thresholds and view detections in the Control Center. As a result, organizations gain quicker, deeper insights into active adversaries and can shut them down in minutes.

Related resources

Blog: Sophos Firewall ranked the #1 overall
Sophos Firewall Free Trial and Demo
Whitepaper: Securing your network from ransomware
Blog: 5 ways your firewall can keep ransomware out
Blog: Firewall hardening best practices
Blog: Secure by Design principles
Sophos recognition

Related security topic: What is a firewall?