What is a Zero-Day Attack?

Zero-day attacks take advantage of vulnerabilities before they’re even recognized, let alone fixed. That essentially weaponizes the unknown against systems and networks. Understanding zero-day attacks calls for embracing unpredictability. So for security leaders, grappling with zero-day attacks is less about chasing perfection and more about cultivating resilience-building systems and strategies capable of withstanding the unexpected, mitigating damage, and restoring trust in the aftermath of disruption. This article provides an overview of these attacks, with notable examples and overall impacts. You can dive into their security here.

What is a Zero-Day Attack? A Deep Dive into Security’s Most Elusive Threat

A zero-day attack exploits a software vulnerability unknown to the vendor or public, leaving no time — zero days — for a patch or mitigation before it’s weaponized. Their elusiveness stems from their ability to bypass traditional security measures, exploiting the gap between discovery and resolution. This class of cyber attack needs both proactive security strategies and efficient incident response to reduce the chance of exposure and limit potential impact.

Zero-day attacks reveal the fragility of modern IT environments, where timing, exploitation, and defense intertwine. The typical attack lifecycle looks something like the following:

• Sourcing a vulnerability: Savvy threat actors can find these issues independently by prowling through code and systems with manual tests or automated tools. Often, state-sponsored actors buy zero-days in the underground marketplace for targeted espionage or critical infrastructure attacks. 

• Weaponization: Once sourced, threat actors convert the vulnerability into a working exploit that’s tailored to bypass defenses and achieve specific malicious goals. This involves reverse-engineering the underlying code or system behavior to understand how it can be triggered and exploited and crafting a payload that executes the flaw once triggered under certain conditions. 

• Target deployment: Often, the weaponized payload gets delivered via phishing emails, malicious attachments, or exploiting internet-facing services in cloud or hybrid environments.

In zero-day attack scenarios, timing is pivotal. Attackers exploit the gap between vulnerability discovery and disclosure. Here is where it’s important to look for behavioral signs of an in-progress attack, using runtime security, rather than the conventional signature-based detection that relies on exploits of known vulnerabilities. 

Threat actors use zero-day exploits to infiltrate systems, escalate privileges, and spy on communications or siphon data. Some industries are more highly targeted by these attacks, often because of the data sensitivity in their networks.  

Zero-Day Entry Points: Where Do Attackers Strike?

Zero-day attacks are growing. And while they can target any environment — on-premises, cloud, endpoint, or IoT — the cloud is a prominent target due to its widespread use and complexity.

Zero-day attacks increased 50% in 2023. The change reflects 97 vulnerabilities exploited in the wild compared to 62 in 2022.

These attacks often target the weakest, most overlooked entry points, from unpatched software to misconfigured cloud environments. That means thwarting them takes an understanding of everything from API security to container security and a shift-right approach to detect problems as soon as they happen. Understanding where attackers strike is critical, as even a single unnoticed vulnerability can compromise an entire system. Here are common entry points.

Entry Point	How Attackers Strike
Web Applications	Exploit web servers, APIs, or logic flaws (XSS, SQL injection, RCE) via automation or social engineering.
Operating Systems (OS)	Target OS services or drivers for privilege escalation, gaining full system control.
Network Infrastructure	Exploit misconfigurations or flaws in protocols (DNS, TCP/IP) and remote services.
Supply Chain	Compromise third-party software or updates, often through insecure dependencies.
Cloud & Containers	Attack misconfigurations, APIs, or orchestration tools like Kubernetes.
IoT Devices	Exploit unsecured firmware or devices lacking encryption and timely patches.
Legacy Systems	Leverage outdated, unpatched systems as backdoors to modern infrastructure.

Some defining evolutions of zero-day attacks in recent years include:

Automated Exploit Tools: Attackers increasingly use automated tools to quickly identify and exploit zero-day vulnerabilities. This means that exploits can spread faster and target a wider range of victims, especially in high-demand, high-value targets like financial institutions.

Advanced Persistent Threats (APT): Nation-state actors and other highly organized groups more often use zero-day vulnerabilities for cyber espionage or sabotage. These groups carry out complex, multi-stage attacks that rely on zero-day vulnerabilities to gain initial access and establish persistence.

Fileless Attacks: Attackers use fileless malware that exploits zero-day vulnerabilities in memory or through scripts, which makes detection and remediation much trickier as these attacks don’t leave traditional traces of activity.

While identifying entry points is essential, early detection and effective response are equally crucial to zero-day defense. 

Notable Zero-Day Attacks

Zero-day attacks are among the most dangerous and costly cyber threats, often targeting high-value systems or data with devastating consequences. These exploits have, therefore, shaped the cybersecurity landscape. Below are some of the most infamous zero-day attacks, their methods, and their impact.

1. Stuxnet (2010)

Stuxnet, a sophisticated worm, exploited four zero-day vulnerabilities in Windows systems to target Iran’s nuclear facilities, causing centrifuges to malfunction. The machinery displayed normal operational data, making the compromise ever more dangerous.

Often cited as the first cyberweapon, Stuxnet demonstrated how zero-day exploits could be used for cyber warfare.

2. Google Aurora (2009)

Chinese state-sponsored attackers exploited a zero-day vulnerability in Internet Explorer to breach Google and other major companies. The attack aimed to access the intellectual property and Gmail accounts of activists.

As a result, Google reconsidered its operations in China. The attack underscored the risks to intellectual property from zero-day exploits of enterprise applications.

3. WannaCry (2017)

WannaCry ransomware leveraged the EternalBlue exploit, a zero-day vulnerability in Microsoft’s SMB protocol leaked by the Shadow Brokers group. The ransomware spread rapidly, encrypting data and demanding payment.

WannaCry disrupted healthcare systems, businesses, and governments worldwide, with an estimated $4 billion in damages. 

4. SolarWinds Supply Chain Attack (2020)

Attackers injected a zero-day backdoor (Sunburst) into SolarWinds’ Orion software. It compromised updates pushed to thousands of organizations, including U.S. government agencies.

The attack demonstrated the dangers of supply chain vulnerabilities, leading to a new understanding of cyber security strategy in the cloud.

5. Log4Shell (2021)

A critical zero-day vulnerability in the Log4j logging library allowed remote code execution. It was quickly weaponized by threat actors, leading to widespread exploitation.

Log4Shell affected millions of applications, from cloud services to IoT devices, exposing the fragility of widely used open-source software.

6. Pegasus Spyware (2016-present)

NSO Group’s Pegasus spyware exploited zero-day vulnerabilities in mobile operating systems like iOS and Android to remotely take control of targeted devices.

Pegasus was used to spy on journalists, activists, and political figures, raising global concerns about privacy, surveillance, and the misuse of zero-day vulnerabilities.

7. Kaseya VSA Ransomware Attack (2021)

REvil ransomware group exploited a zero-day in Kaseya’s remote monitoring and management tool to distribute ransomware to its clients’ networks.

This attack disrupted thousands of businesses globally and showed the cascading risks of zero-day exploits in widely used third-party tools.

The Impact of Zero-Day Attacks

Zero-day attacks exploit the weakest points in our digital ecosystems, and as these notable attacks illustrate, those entry points are everywhere — from vulnerable web applications and misconfigured cloud environments to open-source libraries and third-party tools. Each component represents not only a potential vulnerability but also a call to action for stronger security practices.

Zero-day attacks lead to interrelated effects for companies:

• Financial impact: The average cost of a data breach in 2024 was $4.88 million, with zero-day exploits among the most expensive to mitigate.

• Operational disruption: Zero-day attacks can halt production lines, disrupt supply chains, and shut down operations.

• Data breaches and intellectual property theft: Attackers often use zero-day exploits to steal sensitive data or intellectual property. In 2023, zero-day and supply chain attacks contributed to a 78% increase in data compromises, totaling 3,205 incidents.

• Erosion of trust: Breaches resulting from zero-day attacks can damage brand reputation and erode trust among customers and partners. Companies anticipate that a data privacy crisis would result in a 9% decline in their global annual revenue.

• National security risks: State-sponsored actors often use zero-day exploits for cyber-espionage or sabotage, posing risks to national security. The 2020 SolarWinds attack, which compromised multiple U.S. government agencies, highlights the risk.

Upwind Powers Zero-Day Protection

Upwind’s comprehensive CNAPP powers zero-day protection by leveraging real-time runtime monitoring, behavioral analysis, and detailed runtime Software Bills of Materials (SBOMs) to get visibility into your software supply chain and rapidly identify zero-day vulnerabilities. Unlike traditional defenses, Upwind identifies deviations from your resources’ baseline activities, detecting anomalous activity across workloads, APIs, and resources that could indicate a zero-day exploit in action.

Together, these tools provide an integrated, proactive approach to mitigating and responding to zero-day threats. Want to see it in action? Schedule a demo.

Frequently Asked Questions

How quickly can organizations detect a zero-day attack?

A typical zero-day attack takes 312 days to catch.

Organizations might take days, weeks, or months to detect zero-day attacks. Anomaly detection, threat intelligence, and behavioral analysis are strategies that can shorten detection windows because they find signs of hacker activity even if the vulnerability being exploited is unknown. 

What makes some organizations more vulnerable to zero-day attacks?

Factors like using legacy systems or employing insufficient patching practices make organizations more vulnerable to zero-day attacks. Businesses with complex or highly interconnected networks are often at greater risk due to an expanded attack surface. Finally, some organizations get targeted more due to a perception of high-value data worth stealing or operations that are deemed critical and thus pose a threat to human life if operations were to pause. Examples include:

• Government or defense
• Healthcare
• Financial services
• Technology/Telecommunications
• Energy or utilities

How do zero-day attacks bypass traditional security measures?

Several factors combine to help these attacks bypass traditional defenses. The first is that the vulnerability exploited in the main payload is unknown, the second is a lack of heuristics for unknown threats, and the third is that many zero-day attacks exploit components of a tech environment that security tools often assume are secure. 

What role does AI play in detecting zero-day attacks?

AI improves detection speed for zero-day attacks. Systems based on AI can sift through vast amounts of data for patterns and anomalies that indicate potential threats. Machine learning algorithms can recognize unusual behavior that traditional security tools might miss, such as unauthorized access or abnormal network traffic, even if the attack is based on an unknown vulnerability.

How have zero-day attacks evolved over time?

Earlier zero-day exploits were often opportunistic, targeting widely used applications and systems. Over time, however, zero-day attacks have become more targeted and tailored, often aimed at specific organizations or industries. Nation-state actors are increasingly involved, and their attacks are highly coordinated and well-funded.