Zero-Day Exploits Explained and How to Stay Protected

Many high-profile cyber incidents began with a vulnerability exploit.

The Verizon Data Breach Investigations Report revealed a 180% increase in vulnerability exploitation incidents that eventually led to a data breach.

While vulnerability exploits are indeed a serious threat, zero-day exploits take this category of threats to a whole new level.

So, what is a zero-day exploit?

What are Zero-Day Exploits and How Do They Work?

First, let’s understand a vulnerability exploit.

It’s a technique or tool used in cyber attacks that takes advantage of a vulnerability in software or hardware to gain a foothold in that system.

A zero-day exploit is an advanced variety of that technique. While most exploits target known vulnerabilities, zero-days target unknown vulnerabilities.

Since a zero-day exploit targets a vulnerability unknown to the software vendor, it has profound implications from a security standpoint.

Typically, whenever a vendor discovers or is made aware of a vulnerability in its software, it develops a security fix and includes it in the next update. Customers can then apply the software update and fix the vulnerability in their respective installations.

However, with zero-day vulnerabilities, since the vendor is unaware of the problem, it cannot build a fix. The term “zero-day” refers to the vendor’s developers having “zero days” to fix the flaw before attackers can exploit it.

In this scenario, the upper workflow involving the vendor is non-existent.

As long as the software vendor is unaware, threat actors can take advantage of that vulnerability. They can plant backdoors, install malware, execute privilege escalation and lateral movement, or even exfiltrate data.

Worse, if an in-the-know threat actor shares the zero-day vulnerability (or the exploit itself) in a hacking forum (they often do), other cybercriminals can also jump in.

Imagine all the damage that can happen while a zero-day exploit remains hidden?

Real-World Examples

The zero-day exploit is a favored attack technique because it targets unknown vulnerabilities, making defense difficult and allowing threat actors to stay undetected for long periods. Many high-profile data breaches have stemmed from zero-day exploits.

Here are some recent examples.

Software affected Description Impact
MOVEit Transfer

In 2023, it was reported that the Cl0p ransomware gang conducted a zero-day exploit on MOVEit Transfer.

Many organizations were affected because MOVEit is a widely used managed file transfer server (MFT).
  • 8,000 global organizations
  • Nearly 100 million individuals compromised
Fortra GoAnywhere MFT Also, in 2023, Fortra GoAnywhere, another popular MFT like MOVEit, suffered a zero-day exploit, again carried out by the Cl0p ransomware gang.
  • 1 million patient records compromised
Microsoft Exchange Server

In 2021, multiple zero-day exploits affecting on-premises Microsoft Exchange Servers were discovered.

This gave threat actors unmitigated access to user emails and passwords.
Log4Shell

Also in 2021, the widely deployed logging framework, Log4j, which is incorporated into several Apache projects and popular services such as AWS, Cloudflare, iCloud, Steam, and Tencent QQ, suffered a zero-day vulnerability.

The vulnerability, which was later called ‘Log4Shell’, was known to be exploited by various threat actors.

One of the main reasons all four examples impacted many organizations and users is because cyber criminals carried out those zero-day exploits against highly popular software.

This type of attack is known as a supply chain attack, wherein threat actors target suppliers or vendors to cast a wider net on those suppliers’ vast pool of customers.

As you can see, when you apply a zero-day exploit in a supply chain attack, the result can be catastrophic.

Signs of a Zero-Day Exploit

Despite the seemingly stealthy nature of zero-day-based cyber attacks, remember that the ‘exploit’ is simply a method for getting a foothold into your system. The attack itself may still follow familiar patterns seen in other cyber threats.

You may have difficulty detecting signs if the attacker employs highly evasive techniques. But if not, then you may be able to spot some indicators of compromise (IOCs). Here are some of them:

  • Unusual network traffic – Threat actors generally deploy malware after infiltrating a system through a zero-day exploit. In many cases, the deployed malware primarily communicates with the attacker’s command-and-control (C2) servers to retrieve commands or transmit stolen data. These activities involve outbound connections. So, if you notice network anomalies involving outbound connections, start investigating further.
  • System crashes – If an exploit fails or is improperly executed, it may crash your application or system. Certain exploits also involve malware installations, memory corruptions, file tampering, and other activities that may adversely impact the stability of your system, causing it to crash.
  • Unusual processes – Threat actors may run programs in the background as part of their attack. If you see unusual processes, especially if they’re also consuming an unusually high amount of CPU or RAM, research more about those processes and see if they’re known IOCs.
  • Unrecognized files – IOCs can likewise be new, unexplained files or unexpected changes to critical system files.

Note that you don’t necessarily have to search for these IOCs manually. There are numerous security tools for this purpose.

Responding to a Zero-Day Exploit

Let’s say you just got word that threat actors compromised one of the software applications you’re using through a zero-day exploit. What do you do? Here are some steps you can implement.

  • Activate your incident response protocol – If you already have a plan in place for these scenarios, implement it.
  • Isolate the affected system – This will prevent the threat from spreading to other parts of your infrastructure.
  • Contact your vendor – Ask if they have specific recommended workarounds or risk mitigation steps.
  • Monitor for vendor advisories – Your vendor should release a patch soon, which you should apply as soon as it’s available.
  • Gather threat intelligence – Security researchers are likely on it and posting their findings online. See if they’ve posted any helpful information.
  • Perform threat hunting – If you have the in-house talent, actively search for residual threats and eliminate them.
  • Conduct post-incident analysis – Perform a forensic investigation to understand how cybercriminals carried out the attack and identify the security gaps that let it happen. Using your findings, devise strategies to prevent similar incidents from happening again.
  • Update incident response playbooks – Incorporate lessons learned from the recent incident.

Preventive Measures to Protect Against Zero-Day Exploits

The best strategy in cybersecurity is to prevent or mitigate the risk of a cyber threat before it happens. Here’s what we recommend for zero-day exploits.

  • Operationalize threat intelligence – Incorporate threat intelligence into your daily cybersecurity operations. This will keep you updated with the latest threats (including zero-days) pertinent to your industry or specific elements of your IT infrastructure and allow you to implement appropriate defensive strategies before you’re affected.
  • Operationalize threat hunting – This will enable you to uncover persistent threats, some of which may be elements of zero-day attacks that may be lurking in your infrastructure.
  • Implement network segmentation – This will limit lateral movement and prevent other parts of your infrastructure from being compromised should a zero-day threat slip through your defenses.
  • Adopt patch management – Even if regular patching may only fix known vulnerabilities and not zero-days, this practice can still significantly reduce the risk of a cyber attack.

Security Tools to Protect Against Zero-Day Exploits

To protect your organization against zero-days, you should employ a defense-in-depth or multi-layered cybersecurity strategy.

Here are some security tools that can help in your fight against zero-days. These tools don’t necessarily detect zero-day exploits themselves. Instead, they can detect suspicious behaviors characteristic of typical cyber attacks and execute appropriate responses.

Security Tool Description How It Protects Against 0-Days
Endpoint Detection and Response (EDR)

Monitors and analyzes endpoint devices, such as desktops, laptops, tablets, and phones for malware and other cyber threats.
  • Employs behavioral analytics to analyze events at endpoints in real-time and detect anomalies.
  • Once it detects a potential threat, it can isolate the affected endpoint, send alerts, quarantine suspicious files, or kill suspicious processes.
Next-Generation Firewall (NGFW)

Monitors and analyzes inbound and outbound network traffic.
  • Uses behavioral analytics to detect network anomalies.
  • Uses deep packet inspection (DPI) to check network packets in more detail and uncover suspicious payloads.
  • Uses reputation-based filtering to check an inbound packet’s host of origin and see if it’s known to be malicious.
  • If potential threats are found, the packets in question are blocked.
Threat Intelligence Platforms

Gathers threat intelligence information from external sources. This information may include IOCs, threat TTPs (tactics, techniques, and procedures), and other relevant information.
  • May integrate with EDRs and NGFWs. Those tools can use the threat intel provided to inform their decision-making processes.
  • Cybersecurity analysts can use the threat intel to uncover potential zero-day threats.

Conclusion

Zero-day exploits are unpredictable, but they’re not unstoppable.

While these attacks take advantage of unknown vulnerabilities, the right security strategies can keep your organization prepared.

Continuous monitoring, network segmentation, threat intelligence, and strong incident response protocols all play a role in minimizing risk.

The reality is, new vulnerabilities will always surface. What matters is how quickly you detect, contain, and respond.

The best defense isn’t just about patching what’s known; it’s about being ready for what isn’t.