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What Is a Zero-Day Exploit? Defining an Advanced Cyberattack

Published on May 6, 2022
What Is a Zero-Day Exploit? Defining an Advanced Cyberattack

While businesses have always needed to worry about cybersecurity, the last few years have brought a new level of concern. With the rise of ransomware and other cyber threats, companies are scrambling to protect themselves.

Cyberattacks are pretty common, especially among high-profile enterprises. In fact, over 80,000 attacks happen online every day. With so much money and data available online, every business is a potential target for online threats. And, with the rise of new technology, there are more ways for hackers to get into systems.

One type of threat that has become more prevalent in recent years is the zero-day exploit.

What is a zero-day exploit?

A zero-day exploit is a security flaw unknown to the software developer. Hackers can take advantage of this flaw to gain access to systems or data. Because the developers are unaware of the flaw, they haven't had a chance to patch it.

The term "zero-day" describes the time between when the flaw is discovered and when a patch must be released. That is, "zero-day" implies utmost security urgency.

In some cases, it can take weeks or even months for a patch to be released. This leaves a lot of time for hackers to exploit the flaw. And, if the flaw is discovered in widely-used software, it can affect millions of people.

There are three primary terms to be aware of when dealing with zero-day exploits, each with its definition:

  • Zero-day exploit: the method hackers use to attack systems through unknown vulnerabilities.
  • Zero-day vulnerability: the security flaw that is exploited by the zero-day attack.
  • Zero-day threat/attack: any malware or virus that uses a zero-day exploit to gain access to systems.

Zero-day exploits are often used in targeted attacks. This means that the hacker has specific targets in mind and uses the exploit to gain access to their systems. However, zero-day exploits can also be used in more general attacks, such as ransomware campaigns.

Who carries out zero-day exploits?

Skilled and experienced hackers usually carry out zero-day exploits. They may be part of a larger group or organization in some cases. However, there have been instances where lone wolf hackers have successfully used zero-day exploits. Most people who carry these kinds of actions out fit one of these seven profiles:

Hacktivists: Hacktivists are individuals or groups who carry out attacks for political reasons. They may be protesting against a particular company or government. For example, the 2014 Sony hack that led to the release of private company information was carried out by a North Korean hacktivist group.

Organized Crime: Organized crime groups often use zero-day exploits to gain access to systems and data for financial reasons. They may be after customer credit card information or other sensitive data. In some cases, these groups will also demand a ransom from the company for not releasing the stolen data.

Cyberterrorists: Cyberterrorists are individuals or groups who carry out attacks to cause fear or disruption. They may be trying to interrupt a company's operations or damage its reputation. For example, the Stuxnet virus was used to attack Iranian nuclear facilities and disrupt their operations.

Insiders: Insiders are people who have legitimate access to a system or company's data. However, they use this access for malicious purposes. In some cases, they may be disgruntled employees who want to cause harm to their former employer. Other times, they may be working with an outside group to gain access to the system.

Corporate Hackers: Corporate hackers work within a company to hack its mainframe. These hackers work to find and patch security vulnerabilities before being exploited. In some cases, they may also test the company's security system by trying to break into it.

For-Profit Hackers: These hackers find breaches and then sell the information they've gathered to companies with no intention of actually using it themselves. In some cases, they may also sell the information to the highest bidder on the black market.

Sovereign/State-Sponsored Hackers: These hackers work on behalf of their government to carry out cyber espionage or attacks against other countries. They may be after military secrets or other sensitive information.

Are zero-day exploits dangerous?

Yes, zero-day exploits can be perilous. They can give hackers a way to access systems that they wouldn't be able to get into otherwise. And, because the flaw is unknown, it can be challenging to detect and stop the attack.

Zero-day exploits are often used in targeted attacks, which can be difficult to defend against. However, there are some things that businesses can do to protect themselves.

The best way to defend against zero-day exploits is to have a sound security system, including firewalls, intrusion detection systems, and anti-malware software. It's also essential to keep your software and systems up to date. Doing so will help to close any known security vulnerabilities.

How a zero-day exploit works

Zero-day exploits are just as they sound: developers have precisely zero days to fix the problem before it becomes a very threatening issue. Typically, they work like this:

  1. A system is uploaded with a zero-day vulnerability, unbeknownst to developers
  2. A hacker discovers a security flaw in a piece of software or hardware.
  3. They exploit the flaw to gain access to a system or data.
  4. The developers of the software or hardware are notified of the flaw.
  5. They create a patch to fix the problem.
  6. Users install the patch to protect their systems.

In some cases, the hacker who discovers the breach and the hacker who attacks a system are two different entities. There is a black market for these types of vulnerabilities, which allows for-profit hackers to sell them to the highest bidder. This can make it difficult to track down the original hacker and hold them accountable.

Here are some methods that hackers typically use:


Fuzzing is a type of automated QA testing that looks for software vulnerabilities. It involves feeding random data into a program and then monitoring its response. Usually, this is done with a tool that can generate random data.

Reverse engineering

Reverse engineering is the process of taking something apart and then putting it back together again. Hackers can use this to find flaws in software or hardware. They do this by taking apart the code and then looking for ways to exploit it.

Social engineering

Social engineering is a type of attack that relies on human interaction. Hackers will use this to trick people into giving them sensitive information or access to a system. Common social engineering attacks include phishing and pretexting.

Pretexting is when a hacker creates a false story or scenario to get someone to give them information.

Phishing is when a hacker uses emails, text messages, or social media to try and get someone to click on a malicious link or attachment.

Common targets for zero-day exploits

There are a few common targets for zero-day exploits. Here are some of the most common:

Browsers: Browsers are a common target because they are so widely used. Hackers will often target browsers with attacks like drive-by downloads or clickjacking.

Operating Systems: Operating systems are another common target. This is because they are the foundation on which everything else is built. Hackers will target vulnerabilities in an operating system to gain access to a system or data.

Applications: Applications are also a common target for hackers. This is because they often have a lot of sensitive data. Common attacks against applications include SQL injection and cross-site scripting.

Webpages and CMSs: Webpages and CMSs are often targeted because they are the face of a company. A breach in this area can damage a company's reputation. Common security threats for webpages and CMSs include SQL injection, cross-site scripting, and remote code execution.

Databases: Databases are a common target because they often contain a lot of sensitive data. Especially databases from government agencies, banks, and other entities that handle credit card information, Social Security numbers, and other highly-sensitive information. Hackers will target databases with attacks like SQL injection or buffer overflow.

Internet of Things (IoT) Devices: IoT devices are becoming increasingly common targets for hackers. This is because they are often connected to the internet and have little to no security. Common attacks against IoT devices include DDoS attacks and data manipulation.

Zero-day exploit examples

Believe it or not, zero-day exploits happen more often than you think. Here are a few examples of recent zero-day exploits:

Google Chrome (2021)

In January 2021, a zero-day exploit was discovered in Google Chrome. The exploit allowed hackers to take control of a system by tricking the user into clicking on a malicious link. This exploit was used in targeted attacks against Windows and macOS users.

Zoom (2020)

In July 2020, a zero-day exploit was discovered in Zoom. The exploit allowed hackers to take control of a system by tricking the user into clicking on a malicious link that appeared as a Zoom link does. This attack could only be carried out on users with Windows 7 or older operating systems.

Adobe Flash Player (2016)

In 2016, Adobe Flash Player was exploited by hackers to install ransomware on victims' computers. The exploit was used in a phishing campaign that targeted users in South Korea.

Microsoft Word (2016/2017)

In 2016 and 2017, a zero-day exploit was discovered in Microsoft Word. Hackers exploited CVE-2017-0199 to steal millions of dollars from banks worldwide. This exploit allowed hackers to take control of a system by tricking the user into downloading malware posed as the Microsoft Word application.

Why zero-day exploits are dangerous

Cybersecurity is one of the biggest web development trends, and zero-day exploits are at the forefront.

Zero-day exploits are dangerous because they can be used to take control of a system or steal sensitive data. They are also dangerous because they are often not discovered until after an attack has already taken place. Meaning that victims may not even know that they have been attacked until it is too late.

Here are some of the primary reasons that zero-day exploits are so detrimental:

1) Vulnerabilities aren't always easy to fix

Depending on the severity of the vulnerability, it may not always be possible to fix a zero-day exploit. This is because intricate details often need to be taken into account to patch the hole.

Even if a company can patch the hole, it may not be possible to do so in a timely manner. This leaves systems and data at risk in the meantime. Additionally, once a zero-day exploit is made public, it is only a matter of time before other hackers start using it. This can create a domino effect where many systems are compromised in a short period.

2) Cybercriminals can target your customers or employees

Zero-day exploits can be used to target your customers. This is because hackers can exploit vulnerabilities in order to gain access to sensitive data like credit card numbers and social security numbers. Once they have this information, they can use it to commit fraud or identity theft.

This not only damages your reputation but can also result in financial losses for your company. In some cases, you may even be held liable for the damages.

It is important to note that zero-day exploits can also be used to target employees of a company. This is often done to gain access to sensitive information like trade secrets or customer data.

3) Your company could be held for ransom

Hackers can use zero-day exploits to encrypt files on your system and then demand a ransom for the decryption key. This is known as ransomware.

Ransomware attacks can be devastating for companies because they often result in losing important data or the inability to access critical systems. In some cases, ransomware attacks have even forced companies to close down.

Paying the ransom is not always guaranteed to get your data back. There have been cases where companies have paid the ransom but still not received the decryption key.

Additionally, paying a ransom only encourages cybercriminals to continue carrying out these attacks.

The best way to do this is to protect yourself from DDoS attacks.

How to identify a zero-day attack

There are a few different indicators that you may be under attack from a zero-day exploit.

One of the most common indicators is unusual activity on your network. This can include unexpected traffic spikes or new processes running on your servers. Another indicator is changes in user behavior. This can be things like employees accessing sensitive data that they usually wouldn't or receiving strange emails from unknown senders.

If you notice any of these indicators, it is crucial to take action immediately. The sooner you identify an attack, the easier it will be to mitigate the damage.

To spot these attacks, you could do any of the following:

  • Monitor user reports of your website's performance: Use real user monitoring to understand how users interact with your website. If you notice your website is loading slowly or crashing, this could signify that you are under attack.

  • Check your server logs: Checking your server logs can help you spot unusual activity on your network.

  • Install an intrusion detection system: An intrusion detection system can alert you to changes in behavior that may indicate an attack.

How to protect yourself from zero-day attacks

The best way to protect yourself from zero-day attacks is to have a comprehensive security plan. This should include things like intrusion detection, web application firewalls, and antivirus software.

Keeping your systems up-to-date with the latest patches and security updates is also important. This will help to close any vulnerabilities that hackers could exploit.

You should educate your employees on cybersecurity best practices if you run a company. This includes not opening attachments from unknown senders and not clicking on links in suspicious emails.

You should also use a VPN or a virtual private server when browsing the web. This will help to protect your data from being intercepted by hackers.

Finally, you should always backup your data. This way, if you do become a victim of a zero-day attack, you will be able to recover any lost data quickly.

Final thoughts

Zero-day attacks are a severe threat to individuals, businesses, and governments alike. They can be very dangerous, but by taking the proper precautions, you can help to protect yourself from these types of attacks.

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