Zero-day exploit: explanation and prevention (2024)

A zero-day exploit refers to a security vulnerability in software that was previously unknown to the developers. The term zero day, often also called 0-day, comes from the fact that the manufacturer had 0 days to fix the vulnerability because they knew nothing about it. Cybercriminals use such vulnerabilities to their advantage to gain unauthorized access to systems before developers can close the gap. In this blog post, we will explore the origins of zero-day exploits and discuss effective strategies to address these security risks.

The life cycle of a zero-day exploit

Der Lebenszyklus eines Zero-Day Exploits

1. the emergence of a zero-day

The emergence of zero-day vulnerabilities is due to a complex interweaving of various factors that are frequently observed in the practice of information and cyber security.

One of the main triggers is a lack of knowledge about the various attack possibilities and the corresponding defensive measures. The OWASP Top 10 identifies the most common attacks that software developers should be aware of and effectively defend against. There are two ways of dealing with security: out of interest or through proactive training. The latter requires a clear commitment to security from management. As long as IT security or cyber security is not a priority in the company, there will be a lack of security culture and vulnerabilities will go unnoticed.

However, there are other reasons for the emergence of zero days, such as time pressure in development, cost savings in security aspects, system complexity, the lack of security integration in the development process (security by design) and neglect of security analyses such as penetration tests or security assessments.

It is crucial to address these factors in order to minimize the risk of zero-day exploits. A comprehensive security culture, regular training and the integration of security aspects into the development process are essential in order to identify and proactively eliminate potential vulnerabilities.

2. Finding a zero-day exploit

The threat of creating and exploiting a zero-day exploit is omnipresent and can affect any organization at any time. Attackers use their security expertise to gain an advantage, with the motivation of the attacker determining the course of events – be it as a well-intentioned security researcher or as a malicious attacker (black hat).

Zero-day vulnerabilities can be identified and fixed by various methods, including

  • Bug bounty programs
  • Penetration tests
  • Security assessments
  • Employment of an offensive security expert

The approach of black hats is often similar to that of security researchers, but the difference lies in the motivation. Tools, approach and knowledge are largely the same, depending on experience. For example, a black hat might discover vulnerabilities while conducting a commissioned penetration test but not report them, or pretend to be a benevolent bug bounty hunter and not report vulnerabilities found.

After a zero-day vulnerability has been found and successfully detected on a frequently used system, it is often followed by the development of a small piece of software, such as a bash script, to exploit the vulnerability with one click and be as effective as possible. This is the actual zero-day exploit. This happens in a race against time, both for the attacker and the victim. Quick detection and patching of zero-day vulnerabilities is crucial to minimize potential damage.

3. The attack using a zero-day exploit

Once a malicious attacker has successfully acquired a zero-day exploit, the execution of the same is comparatively effortless. They can automate their attacks or target potential victims, depending on their individual goals. Once the selected targets have been identified, all that remains is to execute the exploit and attack all the chosen targets.

4. Damage caused to the company

The damage caused by the attacker varies according to their objectives. If the attacker’s primary goal is to extort as much money as possible, they will most likely initiate a ransomware attack. If his intention is to collect as much data as possible without being noticed, he will focus on creating a comprehensive data collection. If the attacker’s goal is to cause the company the highest possible costs, they will systematically identify the most critical systems and take targeted measures to cause a long-term outage.

5. Preventive and active detection and elimination of zero-day vulnerabilities

In this situation, the challenge can vary considerably. The measures to be taken depend heavily on the type of system. In the case of purchased systems such as Microsoft Exchange, current messages should be carefully monitored. It is helpful to set up or regularly check the RSS feed from, for example. Following the BSI on is also recommended. Monitoring the media is a quick way to identify warnings about zero-day vulnerabilities.

An automated alternative is to use vulnerability scanners that check the systems accessible inside and outside the company at regular intervals. However, it is advisable to have an expert check the results. This can be done either by an expert within the company or by an external IT security service provider.

Another method of identifying zero-day vulnerabilities before they become exploits is to give security researchers permission to test external systems. This can be done via a bug bounty program or by implementing a vulnerability disclosure policy. The BSI has published a document on vulnerability handling that you can follow. However, it should be noted that publicly granting permission to search for vulnerabilities on your externally accessible systems also carries risks, as malicious hackers could be involved. Therefore, it is recommended to hire an IT security service provider for internal systems. You can find out more about penetration testing in another of our blog posts.

A Security Information and Event Management (SIEM) system like Wazuh is an excellent alternative to commercial SIEMs.Wazuh helps identify vulnerabilities and anomalies in systems and can be configured to automatically block anomalies.However, it is important that Wazuh is set up and maintained by an expert to maximize its effectiveness.

In software development, it is crucial to take a preventative approach to security risks.The establishment of an effective security process plays a central role in this.The earlier security risks are identified, the lower the probability of a zero-day exploit. To explore these topics in more detail, we have already written informative blog posts, the links to which can be found in the attached resources.


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