Protecting Your Network: How To Secure Perimeter Devices From Ransomware

By Ankit Sharma

As enterprises invest in sophisticated endpoint detection and response tools, threat actors have pivoted toward perimeter devices — firewalls, VPN appliances, and load balancers — to gain initial access. These devices are often unmonitored, running outdated firmware, and are rarely subjected to regular patch cycles. Once compromised, they provide attackers with a foothold into the internal network, bypassing traditional security controls and enabling rapid deployment of ransomware payloads.

Why Perimeter Devices Are a Prime Target

Perimeter devices are designed to control traffic entering and leaving a network. Because of their privileged position, they handle massive volumes of sensitive data and maintain high levels of trust inside corporate environments.

Unfortunately, many of these devices run proprietary operating systems with limited logging and visibility. Default credentials, weak configurations, and unpatched vulnerabilities further expose them to exploitation. Unlike endpoints, these devices are seldom covered by traditional EDR tools.

In 2024, vulnerabilities like CVE-2024-21887 in Ivanti Connect Secure VPN and Fortinet’s FortiOS flaws were widely exploited by ransomware operators. Attackers used these vulnerabilities to drop webshells and backdoors, often maintaining persistence for weeks before detonating ransomware.

Initial Access: Exploiting the Edge

Threat actors target perimeter devices for one clear reason: initial access. Compromising an exposed VPN or firewall can grant access without triggering endpoint defenses. Once inside, attackers move laterally to find domain controllers, file shares, and backup systems.

Advanced groups such as LockBit, ALPHV (BlackCat), and Cl0p have been observed exploiting zero-day vulnerabilities or known-but-unpatched flaws in perimeter infrastructure. In some cases, they’ve chained vulnerabilities to achieve code execution, escalate privileges, and disable logging functions.

A 2024 joint advisory by CISA, the FBI, and international partners warned that many ransomware affiliates are actively scanning for vulnerable perimeter devices and leveraging automated tools to exploit them.

Techniques Used to Persist and Evade Detection

After exploiting perimeter devices, ransomware actors deploy various methods to persist and avoid detection:

  • Webshells and Reverse Proxies: Webshells enable remote control of compromised devices. Reverse proxies allow rerouting of traffic, making forensic analysis difficult.
  • Firmware Tampering: In rare but advanced cases, attackers modify firmware to reinstall malware upon reboot.
  • Disabling Logs: Attackers often delete or disable log files to hinder detection and incident response.
  • Traffic Tunneling: By using encrypted tunnels, attackers blend their traffic with legitimate remote access activity.

Impact of Perimeter-Based Attacks

The fallout from compromised perimeter devices is substantial. Once inside, ransomware actors can:

  • Exfiltrate sensitive data before encryption
  • Delete backups to prevent recovery
  • Drop ransomware payloads across multiple systems
  • Disrupt business continuity and services

In October 2024, multiple ransomware operators orchestrated attacks through unpatched SonicWall devices. The incident led to a security team's nightmare as they all scrambled to patch up before being compromised.

How to Secure Perimeter Devices from Ransomware

Organisations must treat perimeter devices as critical assets deserving of the same protection as endpoints and servers.

Regular Patching and Vulnerability Management

Track and patch all perimeter device vulnerabilities using feeds like CISA’s KEV catalog. Use automated tools to scan for outdated firmware and software.

Implement Zero Trust Principles

Don’t assume perimeter devices are infallible. Segment networks, enforce strict identity-based access controls, and restrict east-west traffic.

Enable Logging and Monitoring

Many devices allow integration with SIEMs or syslog servers. Enable logging and set alerts for anomalous behavior like configuration changes or unknown IP access.

Harden Configurations

Disable unused services, enforce strong passwords, and apply vendor-recommended hardening guidelines. Avoid exposing management interfaces to the internet.

Use Network Detection and Response (NDR)

While EDR is great for endpoints, NDR helps detect lateral movement, beaconing, and exfiltration from the network layer.

Simulate Attacks and Test Defenses

Red team exercises or penetration tests focusing on perimeter devices can reveal gaps in visibility and response.

Moving Beyond Reactive Defenses

Ransomware groups move fast. Once a zero-day is disclosed, exploitation can begin within hours. Relying solely on patching is no longer sufficient.

Security teams need to proactively monitor the attack surface, especially exposed services and remote access solutions. Dark web monitoring can reveal chatter about new exploits, while threat intelligence feeds provide indicators of compromise tied to perimeter device exploitation.

Perimeter security is no longer just about firewalls — it’s about visibility, hardening, and rapid response. Ransomware gangs are capitalising on neglected edge devices to bypass sophisticated endpoint defenses. Protecting your network starts with securing its borders.

By treating perimeter devices as first-class citizens in the security architecture, enterprises can deny ransomware actors their favorite point of entry and build resilience against tomorrow’s threats.

(The author is the Senior Director and Head - Solutions Engineering, Cyble)

Disclaimer: The opinions, beliefs, and views expressed by the various authors and forum participants on this website are personal and do not reflect the opinions, beliefs, and views of ABP Network Pvt. Ltd.

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