When it comes to cybersecurity, few terms capture attention like “zero-day.” The phrase has become shorthand for critical vulnerabilities and high-stakes exploits, and in the past year alone, an estimated two million news stories have referenced them. Yet while zero-days are genuinely dangerous, they are actually less common than headlines suggest.
For manufacturers, the greater threat comes from something far less glamorous: the “N-day,” or known vulnerability. Unlike the zero-day, this flaw is one that is already public, already patched, yet remains open in production systems for weeks, months, or even years.
N-days are the workhorses of cybercrime, powering ransomware, data theft, and extortion on a global scale. With manufacturing being the most targeted sector for ransomware, the urgency to close this gap has never been greater.
A Flood of Advisories, But Not Enough Time to Patch
From January through October of this year, the Cybersecurity and Infrastructure Security Agency (CISA) has issued more than 500 Industrial Control Systems (ICS) Advisories. This amounts to over 50 per month, and sometimes the agency drops 20 or more in a single day. During this same period, CISA has added over 200 actively exploited flaws to its Known Exploited Vulnerabilities (KEV) Catalog.
This deluge is overwhelming for operators. The most mature programs will still struggle to keep pace with the constant influx of advisories, even when they affect critical systems where failure or downtime isn’t an option. Criminals know that security teams must continually balance operational uptime against exposure risk, and that gap between disclosure and remediation is exactly where N-day attacks thrive.
Zero-days require significant time and technical expertise to discover. But N-days are different: the exploit roadmap already exists, so attackers simply need to act. This makes them faster, cheaper, and far more efficient, which is why criminals overwhelmingly prefer them.
They also offer a near-guaranteed path to access. Once a vulnerability becomes public, adversaries know they have days, weeks, or months (and, sometimes, even years) to find and exploit unpatched systems. A global marketplace of access brokers and ransomware affiliates then turns that exposure into a fast, scalable business.
As soon as a CVE is published, criminals use automated scanners to sweep the Internet for unpatched systems. These tools, which are increasingly AI-assisted, fingerprint devices and return lists of vulnerable targets in mere hours. Sophisticated ransomware groups run dedicated infrastructure that constantly monitors vulnerability feeds and open-source data for fresh opportunities.
In the ransomware-as-a-service (RaaS) model, access is a commodity. Specialized actors known as Initial Access Brokers (IABs) exploit N-day flaws to gain footholds within organizational networks, often through VPNs, file-transfer systems (FTP), exposed remote gateways, and even firewalls.
Earlier this year, for example, the Cl0p and Qilin ransomware operations exploited known file-transfer and firewall flaws to infiltrate networks at scale. The brokers then sell that access to affiliates who handle encryption, extortion, and monetization. Once breached, a network becomes tradable inventory: administrative credentials, session data, and other system-access artifacts are circulated or auctioned on underground markets.
The same N-day can be reused multiple times (first for reconnaissance or data theft, then later for ransomware), giving known vulnerabilities a long shelf life.
Attackers have also learned to “chain” vulnerabilities to magnify impact. A single, low-risk flaw that would be deprioritized by defenders can become critical when combined with another bug or misconfiguration. Chaining lets adversaries pivot from an exposed public service into deeper-privileged systems, bypass limited compensating controls, or turn a one-off remote code execution into persistent access.
This dynamic can easily blindside defenders as a vulnerability that looked low-risk in isolation quickly becomes a high-value path to full compromise when paired with another exploit.
AI accelerates all of this. Automation and AI tools sold on the dark web assist in generating exploit scripts, summarize patch notes, and correlate CVE information with scan results, enabling attackers to find, chain, and weaponize N-days faster than defenders can schedule maintenance windows or validate fixes.
Operational Factors Behind N-Day Exploitation
Operational complexity remains the biggest enabler of N-day attacks. Even well-resourced manufacturers struggle with structural barriers that slow down patching.
Many plants still depend on legacy or unsupported equipment, where updating systems risks downtime or device failure, leaving teams little choice but to postpone indefinitely.
Industrial networks are deeply interdependent, so a single patch can trigger cascading compatibility issues across PLCs, HMIs, MES, and ERP systems, forcing lengthy testing cycles before deployment. Regulatory and safety standards add further friction through change-control requirements that demand extensive documentation and multi-tier approvals, turning quick fixes into weeks-long processes.
Patching also hinges on vendor timelines. Operators often rely on OEMs or integrators to validate and sign off on updates, creating long certification windows that attackers can exploit. Compounding the issue, many organizations still lack a unified, up-to-date asset inventory across IT and OT environments, leaving vulnerabilities undetected or unprioritized.
Even when visibility improves, lean security teams and competing production demands make it nearly impossible to keep pace with the torrent of advisories and updates. Together, these structural challenges create a persistent patching gap that adversaries are quick to monitor, exploit, and monetize.
How to Keep N-Days from Becoming the Next Breach
Managing N-day risk doesn’t require perfection, but it does demand discipline, visibility, and prioritization.
Focus on what’s exploited, not what’s hypothetical. With hundreds of advisories each year, prioritize vulnerabilities that are actively being exploited. Use the CISA KEV Catalog and sector-specific intelligence to identify which flaws matter most, and patch those first.
Response Plans. Develop, review, and practice cyberattack response plans and integrate cyber investigations into root-cause analysis for all events specific to your IT/OT environment.
Maintain a live asset inventory. You can’t secure what you can’t see. Keep a continuously updated inventory across IT, OT, and IIoT systems to target patches efficiently and avoid surprise exposures.
Define patch windows and testing protocols. Coordinate with production teams to set predictable patch windows. Test in staging or digital-twin environments to prevent downtime, but maintain a regular cadence of updates.
Segment networks and limit remote access. Even if a vulnerability persists, segmentation can prevent lateral movement. Limit IT/OT connectivity and enforce strict access controls for remote sessions.
Monitor for exploitation behavior. Use behavioral analytics and endpoint monitoring to detect exploitation patterns (such as scanning, privilege escalation, lateral movement) before attackers reach production assets.
Apply compensating controls for unpatchable systems. For legacy or unsupported equipment, apply strict network isolation, allow-listing, and hardened configurations. Consider using deception technology or intrusion detection at choke points to spot exploitation attempts early.
Accelerate vendor collaboration. Establish formal SLAs and communication channels with OEMs and integrators for faster patch validation. Where possible, participate in shared testing environments or industry ISACs to reduce duplication and shorten patch cycles.
For ransomware groups and other cybercriminals, N-day vulnerabilities are low-cost, high-yield entry points. Every known flaw left unpatched is an open invitation, and the longer that window stays open, the greater the risk.
While manufacturers can’t patch everything instantly, they can regain control by focusing where it matters most: prioritizing the highest-risk vulnerabilities, shortening patch cycles, and hardening critical systems.
By taking these steps, they can significantly reduce their risk of N-day attacks.
JP Castellanos is the Director of Threat Intelligence for Binary Defense (binarydefense.com).
