Firewall Breach: How Interlock and Others Turned March into a Cybersecurity Minefield

It was an ordinary Tuesday when the alarms started blaring inside a Fortune 500’s security operations center. Within hours, network engineers realized their Cisco firewall - the very shield meant to keep attackers out - had itself become the entry point. By the end of March 2026, this scenario played out across the globe, as threat actors weaponized a record-breaking 31 high-impact vulnerabilities, unleashing a storm of ransomware and cyber-espionage with chilling precision.

Fast Facts

• 31 high-impact vulnerabilities were actively exploited in March 2026, with 29 rated “Very Critical.”
• A zero-day flaw (CVE-2026-20131) in Cisco Secure Firewall Management Center was abused by the Interlock ransomware group for over a month before a patch was released.
• Microsoft and Apple accounted for nearly a third of exploited bugs, highlighting attackers’ preference for widely used platforms.
• At least nine vulnerabilities enabled remote code execution, affecting products from Google, Apple, Microsoft, and others.
• Old vulnerabilities, including a 9-year-old Hikvision bug, remain under active exploitation, underscoring the risk of unpatched legacy systems.

According to intelligence from Recorded Future’s Insikt Group, March 2026 marked a new high-water mark for cyberattacks exploiting software flaws. The most notorious was a zero-day in Cisco’s Secure Firewall Management Center (FMC), which the Interlock ransomware gang leveraged to gain root access on enterprise firewalls. The vulnerability, rooted in insecure deserialization of Java byte streams, allowed attackers to remotely execute arbitrary code - no authentication required. Interlock’s attack chain was textbook: send a crafted HTTP request, fetch a malicious ELF payload, and deploy a cocktail of custom remote access tools to move laterally, escalate privileges, and lay the groundwork for ransomware deployment.

But Cisco was hardly alone. Vendors as diverse as Microsoft, Apple, Google, ConnectWise, and Citrix found their products in the crosshairs. Apple users were hit by sophisticated exploit chains like DarkSword and Coruna, which combined browser and kernel-level exploits to deliver spyware and data-stealing malware. Meanwhile, nine vulnerabilities enabled remote code execution in widely used platforms, amplifying the threat to organizations everywhere.

Public proof-of-concept exploits for 10 of the bugs turbocharged their weaponization, allowing not just elite hackers but also less sophisticated crimeware groups to join the fray. Tools like Nuclei templates enabled defenders to quickly scan for exposure, but attackers often had a month or more head start - especially in the case of Cisco’s zero-day, which was actively abused before most organizations even knew they were at risk.

Perhaps most troubling, old vulnerabilities refused to die. A 2017 Hikvision flaw continued to provide a backdoor for attackers, a stark reminder that yesterday’s bugs can be tomorrow’s breach if left unpatched. Security experts caution that risk management must be guided by real-world exploitation, not just theoretical severity scores, and that defenders need to prioritize based on live threat intelligence and asset visibility.

As March’s carnage shows, the vulnerability arms race is accelerating. Whether it’s a shiny new zero-day or a forgotten flaw from years past, attackers are finding - and exploiting - cracks everywhere. For defenders, the lesson is clear: vigilance, rapid patching, and intelligence-driven risk assessment aren’t just best practices - they’re survival skills in an era where the next breach may already be underway.

WIKICROOK

• Zero: A zero-day vulnerability is a hidden security flaw unknown to the software maker, with no fix available, making it highly valuable and dangerous to attackers.
• Remote Code Execution (RCE): Remote Code Execution (RCE) is when an attacker runs their own code on a victim’s system, often leading to full control or compromise of that system.
• Deserialization: Deserialization converts data into usable program objects. If not done securely, it can let attackers inject harmful instructions into applications.
• Proof: A Proof-of-Concept (PoC) is a demonstration showing that a cybersecurity vulnerability can be exploited, helping to validate and assess real risks.
• Persistence: Persistence involves techniques used by malware to survive reboots and stay hidden on systems, often by mimicking legitimate processes or updates.