What’s a Zero-Day Vulnerability? Prevent Exploits and Attacks

Zero-day vulnerabilities are serious threats. They’re completely unknown to both the vendor and the user. That gives attackers a significant advantage, allowing them to attack systems before patches are available.

Here’s a guide to how zero-day exploits work, real-world examples, and practical tips on keeping these vulnerabilities at bay.

What Is “Zero-Day” in Cybersecurity?

A zero-day vulnerability is a security flaw in software that attackers know about, but vendors don’t. The vendor has zero days to address it from the moment they discover it. In many cases, they only learn of the vulnerability after attackers exploit it.

Security tools typically can’t detect these threats without prior knowledge of the vulnerability, making it easier for attackers to succeed. Bad actors might exploit vulnerabilities to deploy malware, worms, or other malicious tools to compromise systems and steal data.

Zero-day vulnerabilities require proactive defense strategies and continuous monitoring. Even if a vendor can’t prevent risk, they can spot the problem before it spirals out of control.

A Quick Guide to Key Terms

Here’s a breakdown of different terms related to zero-day situations.

Zero-Day Vulnerability

Zero-day vulnerabilities are the security gaps and flaws that attackers exploit. Usually, security researchers, malicious actors, or users discover zero-day vulnerabilities accidentally.

Zero-Day Exploit

A zero-day exploit is a specific method or piece of code that attackers use to take advantage of a vulnerability. These exploits help them bypass security measures and compromise a system. Zero-day exploits are often bought and sold on the dark web, making them accessible to anyone willing to pay.

Zero-Day Attack

Zero-day attacks happen when a hacker uses an exploit to target a vulnerable system. They typically launch zero-day attacks to steal data, gain unauthorized access, or plant malware.

Zero-Day Attack Examples

Zero-day vulnerabilities have real, far-reaching consequences. To show just how impactful they can be, here are some notable examples.

Log4Shell

The Log4Shell vulnerability emerged in 2021 in the popular Log4j logging library. Attackers could use this vulnerability to execute arbitrary code on affected systems, leading to remote control over compromised networks.

The widespread use of Log4j meant that millions of applications were potentially at risk, and the vulnerability was quickly exploited, making it one of the most significant zero-day incidents in recent history. The fallout from Log4Shell forced companies to reassess their reliance on open-source software and prompted swift action to patch their systems.

Microsoft Exchange Zero-Day Vulnerabilities

In early 2021, attackers exploited a series of zero-day vulnerabilities in Microsoft Exchange servers to gain unauthorized access to corporate email accounts and steal sensitive information. The vulnerabilities, collectively known as ProxyLogon, allowed attackers to bypass authentication and execute code remotely.

Google Chrome Zero-Day Vulnerabilities

Attackers found multiple zero-day vulnerabilities in Google Chrome in 2022. One particular zero-day was linked to state-sponsored groups from China, who gained unauthorized access to data via browser and took advantage of remote code execution flaws.

Barracuda Networks Exploit

In 2023, there was a zero-day vulnerability affecting Barracuda’s Email Security Gateway. Attackers were able to gain access and install backdoors for ongoing control. This proves that even enterprise-grade security products are susceptible to zero-day exploits if the vulnerabilities are unknown to users and vendors.

MOVEit Transfer Zero-Day Attack

In mid-2023, attackers exploited a vulnerability in the MOVEit file transfer software, allowing them to gain unauthorized access and steal sensitive data from numerous organizations. This attack became notable due to the wide range of victims—including government agencies and major corporations—and the attackers' ability to deploy web shells for persistent access.

How to Prevent Zero-Day Vulnerabilities

Understanding zero-day security allows you to anticipate potential vulnerabilities and implement defenses as quickly as possible. Here are some proactive strategies and tools to reduce the risk of a zero-day attack affecting your organization:

1. Vulnerability Scanning

Regular vulnerability scanning identifies weaknesses and unusual system behavior that might hint at zero-day threats. Although these scans don’t fully detect zero-day vulnerabilities, they’re valuable for identifying existing risks and unusual system behavior that may hint at an exploit.

2. Patch Management

Effective patch management reduces the attack surface available for exploitation. When you patch known vulnerabilities, attackers have fewer opportunities to chain multiple exploits, limiting their ability to compromise systems. Once a patch becomes available, applying it quickly is critical in preventing zero-day exploits from being used effectively.

3. Attack Surface Management

Attack surface management (ASM) allows you to assess all possible points in your software or network that attackers might target. Proactively managing your attack surface helps you stay aware of what people can see and exploit and protect those vulnerabilities accordingly.

4. Threat Intelligence and Monitoring

Threat intelligence is all about recognizing and monitoring emerging threats, including zero-day exploits. Integrated tools can search for suspicious activities or unusual patterns, helping you quickly identify indicators of compromise that might point to a vulnerability. Real-time threat monitoring can be the difference between detecting an attack early and suffering major damage.

5. Employee Awareness and Training

Human error is one of the easiest attack vectors for cybercriminals to exploit. Train employees on recognizing suspicious activities—like phishing emails, which often initiate a zero-day attack—to prevent risk. The more informed your employees are, the less likely attackers can use social engineering tactics to exploit vulnerabilities.

Zero-Day Vulnerability Protection With Legit Security

Proactive strategies like vulnerability scanning, patch management, threat intelligence, and attack surface management help reduce the risk of zero-day attacks. But zero-day malware and other malicious exploits can pose a serious threat without a multi-layered approach.

Legit Security addresses these challenges by detecting and mitigating vulnerabilities across your software supply chain. By combining real-time visibility with advanced monitoring throughout the development pipeline, Legit Security reduces your attack surface and streamlines collaboration between engineering, DevOps, and security teams.

Stay ahead of attackers and prevent zero-day malware from gaining a foothold with Legit Security’s help. Book a demo today.