The anatomy of a cyberattack: Breaking down zero-day threats

This blog, authored by Sherweb’s Cybersecurity Technical Fellow Roddy Bergeron, dissects zero-day threats and their real-world impact on businesses, providing IT providers with practical strategies for detection, mitigation and incident response when facing these invisible adversaries.

The most dangerous predators don’t announce their presence. They strike without warning, leaving chaos in their wake. In cybersecurity, we call these silent killers “zero-day threats”—vulnerabilities lurking in your systems that nobody knows about until it’s too late.

Think of zero-day exploits as digital quicksand. By the time you realize you’re in trouble, you’re already sinking. And in today’s interconnected world, understanding these threats isn’t just about technical prowess—it’s about survival.

When fiction mirrors reality: Zero-Day in the spotlight

The recent Netflix series “Zero Day” has thrust these cybersecurity nightmares into public consciousness. While Hollywood takes creative liberties, the show’s premise hits uncomfortably close to home. As cybersecurity professionals, we’ve seen how a single zero-day vulnerability can cascade into a crisis that makes fiction look tame.

The show’s global cyber catastrophe might seem far-fetched, but consider this: in 2023, the MOVEit Transfer zero-day vulnerability affected thousands of organizations worldwide, from government agencies to Fortune 500 companies. No dramatic music or movie stars needed, just real businesses, real data and real consequences.

The reality check: Recent zero-day nightmares

Let’s look at four recent zero-day incidents that kept security professionals awake at night:

The MOVEit mayhem (2023)

When the MOVEit Transfer vulnerability emerged, it wasn’t just another CVE number. It became a stark reminder of how interconnected our digital world really is:

• Thousands of organizations affected globally.
• Sensitive data exposed across multiple sectors.
• Cascading impact through supply chains.
• Estimated costs running into billions.

Operation triangulation: The silent iPhone stalker (2023)

These zero-day flaws were exploited in the wild to deliver NSO Group’s the notorious Pegasus spyware, this zero-click zero-day in iOS shattered the illusion of impenetrable Apple security. For MSPs, it was a stark reminder that even the most trusted devices can become silent backdoors into corporate networks:

• Required no user interaction to exploit.
• Affected supposedly “untouchable” Apple devices.
• Demonstrated the sophistication of modern attacks.
• Led to emergency patching for millions of devices.

The Citrix bleed crisis (2023)

CVE-2023-3519 showed how a single vulnerability in infrastructure software can threaten entire business operations:

• Impacted critical NetScaler systems.
• Allowed session hijacking.
• Affected thousands of internet-facing servers.
• Required emergency weekend patching for many MSPs.

The PaperCut pandemonium (2023)

A reminder that sometimes the most dangerous vulnerabilities hide in the most mundane places—like your office printer. The PaperCut vulnerability (CVE-2023-39143) was particularly insidious because:

• Affected common print management systems.
• Exploited by ransomware groups.
• Disrupted operations across education and healthcare.
• Demonstrated how everyday services can become attack vectors.

The anatomy of a zero-day attack

Let’s peel back the layers of these threats. Unlike the dramatic hacks you see on screen, real zero-day exploits are more like invisible burglars who found your house key before you even bought a lock.

The discovery phase

Picture this: somewhere in the vast digital landscape, someone discovers a flaw in widely used software. Maybe it’s a banking application, maybe it’s that PDF reader everyone uses. The finder has two choices: report it responsibly or sell it to the highest bidder. Unfortunately, these vulnerabilities often end up in the wrong hands.

The silent spread

Here’s where it gets interesting (and by interesting, I mean terrifying). Once attackers have a working exploit, they move like ghosts through your network. No alarms, no red flags, no suspicious activity logs—because how can you detect something nobody knows exists?

Recent data tells us that zero-day exploits can circulate in criminal forums for weeks or months before detection. That’s like having someone rummage through your house while you’re sitting in the living room, completely unaware.

The moment of truth

The worst part? Organizations often discover they’ve been compromised only after significant damage is done. By then, the attackers have already set up shop, exfiltrated data or worse, sold access to other criminal enterprises.

Beyond the headlines

Remember that MOVEit Transfer incident I mentioned? Let’s break down what actually happened:

• Day 0: Vulnerability discovered
• Day 1: Exploitation begins
• Day 7: Patch released
• Day 30+: Organizations still discovering they were affected

The kicker? Some companies didn’t even know they were using the vulnerable software because it was buried in their supply chain. That’s the thing about zero-day threats — they don’t just exploit technical vulnerabilities; they exploit our assumptions about security.

The business impact: Beyond the technical

For MSPs, zero-day threats aren’t just technical challenges, they’re business earthquakes waiting to happen:

Financial tremors

• Professional liability claims can skyrocket.
• Cyber insurance premiums often increase post-incident.
• Emergency response costs can strain resources.
• Client compensation and remediation expenses.

Reputation aftershocks

• Client trust takes years to build, minutes to break.
• Market perception can affect future growth.
• Industry standing among peers.
• Partner relationship strain.

Compliance cascade

• Regulatory reporting obligations.
• Documentation requirements.
• Audit trail maintenance.
• Legal exposure management.

The human element: What they don’t tell you

Let’s talk about something we often overlook, the emotional toll of being the last line of defense:

Weight of responsibility

• Being the bearer of bad news to clients.
• Making high-stakes decisions under pressure.
• Balancing transparency with panic prevention.
• Managing team burnout during crisis response.

Professional pride

• Successfully preventing major breaches.
• Building resilient systems that withstand attacks.
• Earning client trust through competence.
• Growing stronger from each challenge.

Building your zero-day defense

Now for the part you’ve been waiting for:  how to better protect yourself and your clients. While we can’t prevent zero-day vulnerabilities from existing, we can make attackers work a lot harder to exploit them.

1. Assume the worst

Remember that old saying about paranoia and survival? In cybersecurity, it’s not paranoia if they’re really out to get you. And they are. Some practical steps:

• Segment your networks like you’re planning for a zombie apocalypse.
• Monitor traffic patterns like a suspicious parent checking their teenager’s phone.
• Question everything! Especially those “trusted” applications.
• Use the principle of least privilege access.

2. Layer your defenses

If you’re only running antivirus and a firewall, you might as well be defending yourself with a paper shield. Modern defense requires:

• Behavioral analytics (because normal users don’t usually download the entire customer database at 3 AM).
• Zero-trust architecture (trust no one, verify everything).
• Continuous monitoring (because attackers don’t take coffee breaks).

3. Train like you fight

Your employees are either your strongest defense or your biggest vulnerability. Make security training:

• Relevant (use real examples, not theoretical scenarios).
• Engaging (yes, you can make security fun—I’ve seen it happen)
• Continuous (one annual training session is like having one annual shower).

Quick response guide: When zero-day becomes ground zero

When a zero-day announcement hits, here’s your tactical playbook:

First 15 minutes

1. Assess scope and potential impact
2. Identify affected systems and clients
3. Initiate internal communication protocols
4. Begin documentation process

First hour

1. Establish command structure
2. Deploy monitoring for exploitation attempts
3. Prepare client communication drafts
4. Begin mitigation planning

First four hours

1. Implement temporary mitigations
2. Send initial client notifications
3. Coordinate with vendors
4. Plan resource allocation

Communication templates

• Initial Alert: “We are actively monitoring the [vulnerability name] situation…”
• Status Update: “Our team has implemented initial safeguards…”
• Resolution Notice: “Patches have been tested and deployment is scheduled…”

The evolution of zero-day threats

The landscape is changing faster than ever. We’re seeing:

• AI-powered exploit development.
• Supply chain attacks becoming more sophisticated.
• Zero-day vulnerabilities being weaponized faster than ever.

But here’s the silver lining: we’re getting better at detection and response. New technologies like machine learning are helping us spot anomalous behavior before it becomes a breach.

Taking action: Your next steps

1. Audit your current security posture (be honest, how many “temporary” fixes are still in place?).
2. Implement continuous monitoring (because “set it and forget it” is for slow cookers, not security).
3. Develop an incident response plan (and please, test it before you need it).

Final thoughts

Zero-day threats aren’t going away. But neither are we. Understanding that these threats aren’t just technical problems, they’re business challenges that test our expertise, resilience and leadership is a start. But with proper preparation, clear protocols and a dash of healthy paranoia, we can turn these crises into opportunities to demonstrate our value and protect our clients.

Ready to strengthen your zero-day defenses? Don’t wait for a zero-day exploit to expose your vulnerabilities. Contact Sherweb today for a security assessment that goes beyond the basics. Because in cybersecurity, tomorrow might be zero day.