Zero-Day Exploit Examples (2023): The 10 Worst Attacks Ever

By Tibor Moes / Updated: May 2023

Zero-Day Exploit Examples (2023): The 10 Worst Attacks Ever

Zero-Day Exploit Examples

Imagine you’re in a castle under siege. The enemy has found a hidden door that you didn’t know existed. They sneak in, creating chaos and destruction before you can barricade the door. This is the digital equivalent of a zero-day exploit. In this article, we’ll dive into the worst such ‘sneak attacks’ in history.


A zero-day exploit is like a thief finding an unlocked door no one knows about. It’s a vulnerability in software that the developers don’t know exists, so there’s no fix. When hackers discover it, they exploit it to wreak havoc before a solution can be made.

  1. Code Red Worm (2001): Exploited a buffer overflow vulnerability in Microsoft’s Internet Information Services (IIS) web server.
  2. SQL Slammer (2003): This worm exploited a buffer overflow vulnerability in Microsoft’s SQL Server and Desktop Engine database products.
  3. Sasser Worm (2004): Exploited a vulnerability in Microsoft’s Windows XP and Windows 2000 operating systems.
  4. Stuxnet Worm (2010): This worm exploited four different zero-day vulnerabilities in Microsoft’s Windows operating system, primarily targeting Iran’s nuclear facilities.
  5. Heartbleed (2014): This bug affected the OpenSSL cryptography library, which is widely used in the transport layer security protocol.
  6. Shellshock (2014): A vulnerability in the Unix Bash shell that was often used for remote code execution.
  7. Petya/NotPetya (2017): Ransomware that exploited a vulnerability in Microsoft’s Windows operating system, which was initially exposed by the EternalBlue exploit.
  8. WannaCry (2017): This ransomware also exploited the same vulnerability in Microsoft’s Windows operating system as Petya/NotPetya.
  9. Spectre and Meltdown (2018): These two related vulnerabilities affected virtually all computers with modern processors by exploiting flaws in their design to leak sensitive information.
  10. BlueKeep (2019): A vulnerability in Microsoft’s Remote Desktop Protocol, which could allow for remote code execution.

Don’t become a victim of cybercrime. Protect your devices with the best antivirus software and your privacy with the best VPN service.

Zero-Day Exploit Examples In-Depth

1. Code Red Worm (2001)

In the summer of 2001, a digital epidemic swept across the world. A seemingly innocuous buffer overflow vulnerability in Microsoft’s Internet Information Services (IIS) web server software turned into a devastating cyber attack. The assailant was an unknown entity, dubbed the Code Red worm.

Code Red worm, which lasted from July 13 to July 20, 2001, was a hit-and-run affair. Its perpetrators remain unknown, an elusive shadow in the murky world of cybercrime. Yet, their actions had global implications, reaching far beyond any national boundaries.

The worm targeted businesses and government agencies using Microsoft’s IIS software, a popular choice for web servers. It defaced websites, replacing them with the message, “Hacked by Chinese!”. It’s estimated to have infected over 350,000 servers worldwide, demonstrating the frightening scale of such an exploit.

Financially, the Code Red worm was a disaster, causing an estimated $2.6 billion in damages. It was a loud wake-up call for the digital world, underscoring the importance of regular software updates and robust cybersecurity measures.

In terms of data compromise, Code Red was less about stealing data and more about causing disruptions. Its main purpose was to spread as far and wide as possible, wreaking havoc on web servers globally.

The worm was eventually brought under control when Microsoft released a patch to fix the IIS vulnerability. But the effects of the Code Red worm were long-lasting, prompting a significant increase in cybersecurity awareness and the importance of promptly addressing software vulnerabilities.

As far as legal consequences go, the mystery surrounding the identity of the worm’s creators means they have not faced justice – a chilling reminder of the anonymity and impunity that often shrouds cybercrime.

2. SQL Slammer (2003)

Two years after the Code Red worm, in January 2003, another zero-day exploit made headlines: the SQL Slammer worm. It exploited a buffer overflow vulnerability in Microsoft’s SQL Server and Desktop Engine database products. The perpetrators? Again, unknown. But their handiwork had a lasting impact.

The SQL Slammer worm was a blitzkrieg attack, lasting for only a few minutes on January 25, 2003. But in that brief time, it managed to infect nearly 75,000 servers worldwide. The attack was indiscriminate, affecting businesses, governments, and individuals alike, underlining the fact that in the digital age, nobody is safe.

The financial damage from the SQL Slammer worm was significant, with estimates ranging from $1 billion to as high as $1.2 billion. The worm disrupted everything from bank operations to air travel, causing widespread chaos and underscoring the interconnectivity of our digital world.

The nature of the compromised data varied widely, given the diverse range of affected entities. However, the worm’s primary function was not to steal data but to propagate itself as quickly as possible.

The response was swift. Microsoft released patches to fix the vulnerability, and network operators implemented measures to block traffic on the port used by the worm. This swift action mitigated the worm’s impact, highlighting the importance of rapid response in cybersecurity.

As with the Code Red worm, the SQL Slammer’s creators have never been identified or brought to justice. The anonymity of cybercriminals remains one of the most significant challenges in the fight against cybercrime. Yet, these incidents serve as a stark reminder of the importance of constant vigilance and robust cybersecurity measures.

3. Sasser Worm (2004)

In April 2004, another cyber calamity struck. This time, it was the Sasser worm, which exploited a vulnerability in Microsoft’s Windows XP and Windows 2000 operating systems. The perpetrator was not a faceless, unknown entity, but a German student named Sven Jaschan, who was later apprehended and convicted.

The Sasser worm was a rapid-fire attack, spreading worldwide within a few days. It didn’t discriminate among its victims, targeting businesses, individuals, and even critical infrastructure. For instance, Delta Airlines had to cancel several flights, and the British Coastguard’s mapping services were temporarily taken offline – underscoring the real-world consequences of such digital onslaughts.

The geographic scope of the Sasser worm was truly global, affecting millions of computers around the world. The financial damage was colossal, reaching an estimated $18 billion.

Unlike its predecessors, the Sasser worm didn’t aim to compromise data; instead, its main function was to slow down and crash systems, causing widespread disruption.

Once the source of the attack was identified, Microsoft offered a bounty, which led to Jaschan’s arrest. Subsequently, patches were released to fix the vulnerability, and infected systems were cleaned. The aftermath of Sasser led to a heightened focus on cybersecurity and the potential havoc that even a single individual could wreak on the world.

As for legal consequences, Jaschan was tried in Germany and received a 21-month suspended sentence. This was one of the first high-profile cases where a cybercriminal faced tangible legal repercussions, marking a crucial turning point in the fight against cybercrime.

4. Stuxnet Worm (2010)

The year 2010 marked a new era in cyber warfare, with the discovery of the Stuxnet worm. Unlike previous attacks, Stuxnet was not the work of independent hackers or cybercriminals but a state-sponsored attack. Although it was never officially confirmed, it’s widely believed that the U.S. and Israel jointly developed Stuxnet to disrupt Iran’s nuclear program.

The Stuxnet attack was highly targeted, affecting specific industrial systems in Iran’s nuclear facilities. However, the worm also spread inadvertently to other countries, affecting thousands of systems worldwide.

The financial implications of Stuxnet are hard to estimate, given its primary objective was to cause physical damage to Iran’s nuclear facilities rather than to steal information or money. However, the cost of developing and deploying a cyber weapon of this sophistication is believed to be in the millions of dollars.

In terms of compromised data, Stuxnet was more about causing physical disruption than stealing information. It manipulated the industrial control systems to cause equipment to malfunction, marking the first known case of a cyber attack causing physical damage.

Following the discovery of Stuxnet, cybersecurity firms and government agencies worldwide worked together to analyze and neutralize the threat. The aftermath of Stuxnet saw a significant shift in the landscape of cybersecurity, with the realization that cyber weapons could cause physical destruction and potentially be used in warfare.

The legal consequences of Stuxnet are non-existent, largely due to the covert nature of the operation and the lack of international law governing state-sponsored cyber attacks. Nevertheless, Stuxnet marked a new chapter in the world of cybersecurity, serving as a stark reminder of the potential use of zero-day exploits in international conflict.

5. Heartbleed (2014)

In April 2014, the digital world’s heart skipped a beat with the discovery of Heartbleed, a bug that affected the OpenSSL cryptography library, widely used in the transport layer security protocol. Unlike previous examples, Heartbleed was not a worm but a serious vulnerability that could expose sensitive information.

Heartbleed was not an attack in itself, but an open door for potential cyber thieves. Its discovery sent shockwaves around the world, as OpenSSL is used by about two-thirds of all websites to secure and encrypt online communication.

The exact perpetrators exploiting this vulnerability remain unknown, emphasizing the digital realm’s anonymity. The targets were as diverse as the internet itself, with everyone using OpenSSL potentially being at risk.

The financial damage of Heartbleed is hard to quantify because the bug’s primary danger was the potential exposure of sensitive data. However, the cost to businesses and individuals for upgrading systems, creating patches, and responding to potential data breaches was significant.

In terms of data compromise, Heartbleed had the potential to expose everything from passwords and personal information to credit card details and sensitive government data. It was a stark reminder of the fragility of digital security and the constant need for vigilance and updates.

The countermeasures taken against Heartbleed were swift and worldwide. Patches were quickly developed and implemented, and users were encouraged to change their passwords after the patches were applied. It marked a global, cooperative effort to close the digital door that had been unwittingly left open.

As for legal consequences, since Heartbleed was a vulnerability rather than a specific attack, no legal action could be taken. However, it served as a wakeup call for better security practices and standards in the software industry.

6. Shellshock (2014)

Just months after Heartbleed, another significant cyber threat emerged in September 2014. Dubbed Shellshock, it was a vulnerability in the Unix Bash shell, often used for remote code execution.

Shellshock, like Heartbleed, was not an attack but a vulnerability that could be exploited. It had the potential to affect millions of computers and other devices, including web servers and operating systems.

The perpetrators who exploited Shellshock remain unknown, but the implications of this vulnerability were massive. Any system using the Bash shell, from servers to personal computers, and even some embedded systems, could be targeted.

The financial damage caused by Shellshock is difficult to estimate, as it’s not known how many systems were compromised. However, the cost of patching systems and ensuring security was considerable.

Shellshock could allow an attacker to gain control over a targeted system, meaning any data on that system could potentially be compromised. This ranged from personal information to financial data, and sensitive corporate or government information.

Countermeasures against Shellshock were undertaken globally, with patches being developed and implemented to close the vulnerability. The response to Shellshock demonstrated the importance of collaboration and quick action in the face of a widespread cyber threat.

As with Heartbleed, Shellshock was a vulnerability rather than a specific attack, so there were no direct legal consequences. However, it served to further highlight the need for robust security practices and the potential dangers lurking in even the most taken-for-granted areas of our digital infrastructure.

7. Petya/NotPetya (2017)

In June 2017, a new cyber terror hit the digital streets: Petya. Or, more accurately, its far more dangerous variant, NotPetya. It was a ransomware attack that exploited a vulnerability in Microsoft’s Windows operating system, initially exposed by the EternalBlue exploit, believed to be developed by the U.S. National Security Agency.

The attack was swift and devastating, starting in Ukraine and then spreading globally within a few hours. The attackers remain unknown, but their targets were mainly businesses. However, the geographic scope extended far beyond Ukraine, affecting organizations worldwide.

The financial damage caused by NotPetya was monumental. The total cost of the damage is estimated to be over $10 billion, making it one of the costliest cyber attacks in history.

The number of people affected was in the thousands, as the worm quickly spread through corporate networks. The nature of the compromised data varied, as it encrypted all types of data on the infected systems and demanded a ransom to unlock it.

Countermeasures were quickly put into place, with patches developed to prevent the spread of the worm. However, the aftermath of the attack was a wakeup call for many organizations about the importance of keeping their systems up to date and the potential severity of ransomware attacks.

There were no direct legal consequences for the NotPetya attack, as the perpetrators remain unknown. However, the event highlighted the potential damage of cyber warfare and the importance of robust cybersecurity measures.

8. WannaCry (2017)

Just a month before NotPetya, in May 2017, another ransomware made headlines: WannaCry. Like NotPetya, it used the EternalBlue exploit to target a vulnerability in Microsoft’s Windows operating system.

WannaCry was a global catastrophe, affecting hundreds of thousands of computers in over 150 countries within a day. The perpetrators were believed to be the North Korean hacker group known as Lazarus, marking this as a potential state-sponsored cyber attack.

The victims of WannaCry ranged from individuals to businesses and government organizations. Notably, the UK’s National Health Service was severely affected, causing significant disruptions to healthcare services.

Financially, WannaCry caused an estimated $4 billion in damages, marking it as one of the most destructive cyber attacks to date.

The ransomware encrypted user data, demanding a ransom paid in Bitcoin to unlock the affected files. This put a vast amount of personal and sensitive data at risk.

The attack was mitigated when a kill switch was discovered in the ransomware’s code by a cybersecurity researcher. This significantly slowed its spread, but not before it caused significant damage. In the aftermath, organizations worldwide were prompted to update their systems and implement stronger security measures.

As for legal consequences, despite the strong suspicions towards the Lazarus group, no formal charges have been made. This case served as another stark reminder of the potential scale and impact of ransomware attacks, and the increasing involvement of state-sponsored entities in cybercrime.

9. Spectre and Meltdown (2018)

In the beginning of 2018, two unprecedented vulnerabilities, Spectre and Meltdown, were revealed. Unlike previous cyber threats that exploited software, these targeted the hardware level, specifically the central processing units (CPUs) designed by Intel, AMD, and ARM.

Spectre and Meltdown weren’t attacks but vulnerabilities that could be exploited to access sensitive data directly from the memory of running programs. The disclosure of these vulnerabilities sent shockwaves across the tech world, given that billions of devices worldwide use these processors.

The potential attackers in this case could be anyone who can run programs on the affected devices. This could range from individual hackers to large, organized cybercrime groups or state-sponsored entities.

The financial damage caused by Spectre and Meltdown is difficult to estimate, as their primary threat was potential data exposure rather than direct financial loss. However, the cost to the manufacturers for developing and deploying patches, and to users for implementing these updates, was considerable.

The data that could be compromised by exploiting these vulnerabilities was extensive. It ranged from personal information to passwords and encryption keys, emphasizing the severity of the threat.

Countermeasures were quickly implemented once the vulnerabilities were disclosed. Chip manufacturers, operating system vendors, and cloud providers all worked to develop and deploy patches to mitigate the threats posed by Spectre and Meltdown.

There were no direct legal consequences as these were vulnerabilities rather than attacks. However, the discovery of Spectre and Meltdown marked a significant moment in the field of cybersecurity. It underscored the potential for hardware-level vulnerabilities and highlighted the need for robust security considerations in chip design.

10. BlueKeep (2019)

In May 2019, a severe vulnerability known as BlueKeep was discovered in Microsoft’s Windows operating system. Similar to Heartbleed and Shellshock, BlueKeep was not an attack but a vulnerability that, if exploited, could allow an attacker to remotely execute code on a targeted system.

The discovery of BlueKeep triggered alarm bells in the cybersecurity world. The vulnerability was present in older versions of Windows that are still widely used in many businesses, potentially putting millions of systems at risk.

The potential perpetrators of a BlueKeep exploit could be anyone from individual hackers to state-sponsored entities, underlining the wide-ranging threat posed by such vulnerabilities.

The financial damage that could be caused by a successful BlueKeep exploit is hard to estimate, but given the potential number of vulnerable systems, it could be significant.

If exploited, BlueKeep could give an attacker control over a targeted system, compromising any data stored on that system. This could range from personal data to sensitive corporate or government information.

In response to the discovery of BlueKeep, Microsoft released patches for all affected versions of Windows, including those no longer officially supported. This marked a significant response to a potential cyber threat, demonstrating the importance of proactive measures in cybersecurity.

As with other vulnerabilities, there were no legal consequences for BlueKeep. However, it served as a stark reminder of the importance of keeping systems updated and the potential dangers posed by vulnerabilities in widely used software.


Just as we wouldn’t leave our homes or cars unlocked, we shouldn’t leave our digital lives unprotected. The world of cybersecurity can seem daunting, but taking simple, proactive steps can significantly reduce the risk of falling victim to a cyber attack.

First and foremost, keep your devices updated. Many of the exploits discussed in this article took advantage of vulnerabilities in outdated software. Regularly updating your devices ensures that you’re protected by the latest security patches.

Investing in one of the best antivirus software for Windows 11 like Norton, Bitdefender, McAfee, Panda or Kaspersky is another essential step. Good antivirus software can detect and block many threats before they can cause damage.

Remember, cybersecurity is not a one-time task, but an ongoing responsibility. Staying informed about the latest threats and understanding how to protect yourself is key.

Here are some trusted resources where you can learn more about cybersecurity:

By being vigilant, staying informed, and taking active steps towards securing our digital lives, we can all contribute to a safer internet. Remember, cybersecurity starts with you!

Author: Tibor Moes

Author: Tibor Moes

Founder & Chief Editor at SoftwareLab

Tibor is a Dutch engineer and entrepreneur. He has tested security software since 2014.

Over the years, he has tested most of the best antivirus software for Windows, Mac, Android, and iOS, as well as many VPN providers.

He uses Norton to protect his devices, CyberGhost for his privacy, and Dashlane for his passwords.

This website is hosted on a Digital Ocean server via Cloudways and is built with DIVI on WordPress.

You can find him on LinkedIn or contact him here.

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