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What is Zero-Day Vulnerability? A Guide for 2024

What is Zero-Day Vulnerability? A Guide for 2024

A zero-day vulnerability is a digital time bomb that can go off at any time. These vulnerabilities are far more dangerous than others since they remain hidden and unaddressed… until it's too late.

Alarmingly, the frequency of zero-day attacks has seen a marked increase in recent years, with over 40 vulnerabilities detected in both 2022 and 2023. This trend underscores the urgent need for developers to understand these vulnerabilities' origins and proactively address them. Ignoring these threats only increases the risk of data breaches, financial losses, and downtime. 

What is a Zero-Day Vulnerability?

A zero-day vulnerability refers to a software security flaw unknown to those responsible for patching or fixing it. The term ‘zero-day’ describes the fact that the developers have zero days to fix the issue because it has already been discovered by others, usually hackers or security researchers.

Cybercriminals find these vulnerabilities and use them to launch attacks, known as zero-day exploits. A zero-day attack happens when these exploits are actively used to cause damage, like stealing data or gaining unauthorized access.

Who is behind these attacks?

Zero-day exploits can be executed by various actors, including cybercriminals, hacktivists, and those involved in cyber warfare. Their motivations vary, but the impact is often severe.

Who is at risk?

The short answer is... everyone. Individual users, large companies, government agencies, and even public institutions can be targets. The targets can include systems ranging from personal devices to Internet of Things (IoT) gadgets and essential infrastructure, and any entity with digital infrastructure and valuable data can be a target. 

Zero-Day Vulnerability Cycle

What is the Impact of a Zero-Day Vulnerability?

Zero-day vulnerabilities rank alongside OWASP’s top 10 vulnerabilities as highly significant threats, capable of putting entire organizations at risk of financial, reputational, and legal damage, plus operational downtime. Here are some other impacts. 

  1. Extended Discovery Time

  2. Black Market Activity

  3. Risk of Corporate Espionage and Cyber Warfare

3 Examples of a Zero-Day Vulnerability

Here is a summary of the three most popular (and rife) zero-day vulnerabilities.

Chrome Zero-Day Vulnerability (CVE-2024-0519):

Chrome Zero-Day Vulnerability (CVE-2024-0519)

  • What happened: In 2024, Chrome experienced a zero-day attack due to a memory corruption bug in the V8 JavaScript engine. This vulnerability, called CVE-2024-0519, allowed remote attackers to exploit heap corruption through a crafted HTML page.

  • Impact: The bug posed a significant risk to Chrome users, potentially allowing attackers to execute arbitrary code on the user's system. The high-severity attack is just one in a string of zero-day bugs discovered in Chrome, which acts as a gateway to users’ applications, websites, PDFs, and more. 

  • Discovery: The vulnerability was discovered by an anonymous researcher and reported on January 11, 2024.

  • Solution: Google responded promptly by releasing an update for the Chrome browser, including crucial security fixes to neutralize this zero-day vulnerability.


Log4Shell Zero-day Vulnerability

  • What happened: Log4Shell was a critical vulnerability in the Log4j library discovered in 2021. It allowed attackers to execute arbitrary code remotely.

  • Impact: This vulnerability affected millions of devices and systems running Java applications, posing a severe security threat. Following the disclosure of the Log4Shell vulnerability, there were one million attack attempts in just 72 hours and over 22 million vulnerable app installations.  

  • Discovery: A security team member from Alibaba Cloud reported this vulnerability, which had been present since 2013.

  • Solution: A patch was released, and developers were urged to update to the latest version of Log4j to mitigate the risk.

Zerologon (CVE-2020-1472)

Zerologon (CVE-2020-1472) Vulnerability

  • What happened: Zerologon, discovered in 2020, was a severe vulnerability in Microsoft's Netlogon protocol, affecting Microsoft Active Directory domain controllers.

  • Impact: This vulnerability allowed attackers to impersonate any computer, including the domain controller, and potentially lead to a domain takedown attack. From here, the bad actor can take control of the whole network, leaving businesses exposed to crippling ransomware attacks. 

  • Discovery: Researchers at Secura identified and published information about this flaw.

  • Solution: Microsoft released a patch in August 2020 and urged users to update their systems immediately.

How Do You Identify a Zero-Day Vulnerability?

Detecting a zero-day vulnerability is challenging since it appears in multiple forms, such as missing authorizations, bugs, encryption issues, or broken algorithms. However, several ways exist to identify any exploits or abnormalities that could have resulted from a zero-day vulnerability.

1. Employ UEBA (User and Entity Behavior Analytics)

Actionable Tips:

  • In recent years, UEBA systems (such as open-appsec and SpectralOps) have become specialized, which makes their algorithms more effective at zoning in on specific issues. 

  • Regularly review the alerts and investigate any potential security incidents.

2. Use Vulnerability Scanning Tools and Platforms

Actionable Tips:

  • Use tools like SpectralOps, Nessus, or Qualys to scan your network and systems after deploying new software updates or adding new devices.

  • Use the results to prioritize and remediate identified vulnerabilities.

3. Analyze Known Malware Signatures

Actionable Tips:

  • Use tools like Malwarebytes or McAfee to conduct regular scans for malware.

  • Regularly update your threat intelligence database.

  • Cross-reference any detected malware with known vulnerabilities.

4. Conduct Frequent Security Audits

Actionable Tips:

  • Establish a routine for conducting comprehensive security audits.

  • Combine automated security tools with manual inspections for a thorough security audit.

  • Review and update your security policies and incident response plans based on audit findings.

5 Ways to Protect Against a Zero-Day Vulnerability

However, there are several ways that you can keep your eyes peeled for these treacherous attacks. 

1. Patch Management and Regular Software Updates

Actionable Tips:

  • Establish a schedule for regularly checking and applying updates for all software.

  • Use patch management tools to automate this process. For example, you can use Group Policy to set up automatic updates or PowerShell scripts to manage updates across the network.

2. Use Only What You Need

Actionable Tips:

  • Conduct an audit of all software and applications in use and remove any that are not essential.

  • Use an application whitelisting software like AppLocker (Windows) or SELinux (Linux).

  • Implement SELinux policies to enforce the minimum necessary privileges for applications and services.

3. Regular Vulnerability Management

Actionable Tips:

  • Use tools like SpectralOps for regular vulnerability scanning and assessment.

  • Use reports generated from the tools to prioritize and remediate risks.

4. Implement ZTA (Zero Trust Architecture)

Actionable Tips:

  • Deploy Zero Trust principles across your network.

  • Implement multi-factor authentication, least privilege access, and micro-segmentations.

5. Employ a WAF (Web Application Firewall)


open-appsec is an open-source project that builds on machine learning to provide pre-emptive web app & API threat protection against OWASP-Top-10 and zero-day attacks. It simplifies maintenance as there is no threat signature upkeep and exception handling, like common in many WAF solutions.

To learn more about how open-appsec works, see this White Paper and the in-depth Video Tutorial. You can also experiment with deployment in the free Playground.


Experiment with open-appsec for Linux, Kubernetes or Kong using a free virtual lab

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