A Brief Introduction to Zero-Days

Zero-day vulnerabilities, unknown to software vendors and without available patches, create a perfect storm in which attackers gain a critical time advantage. 

Zero is not better than nothing.

7 min read  |  Reflare Research Team

All the drama

With Netflix's new thriller series Zero Day capturing global attention, the concept of zero-day vulnerabilities has entered mainstream consciousness. While the show depicts a synchronised nationwide cyberattack with Hollywood flair, the reality of zero-day vulnerabilities is more nuanced and perhaps more concerning.

Origins and Early History

The concept of zero-day vulnerabilities predates the term itself. In the 1970s and 1980s, as computer systems became more prevalent, security researchers and early hackers discovered software flaws that could be exploited before developers knew about them. The Morris Worm of 1988, while not explicitly called a zero-day attack, exploited previously unknown vulnerabilities in Unix sendmail, finger, and rsh/rexec to infect approximately 10% of all internet-connected computers.

The term "zero-day" emerged in the 1990s within the software piracy (a.k.a. warez) community. Originally, it referred to copyrighted software that had been cracked and distributed on the same day as its release. As the security landscape evolved, the term shifted to its current meaning in cybersecurity.

The Commercialisation of Zero-Days

By the early 2000s, a significant shift occurred when researchers realised the monetary value of discovering these vulnerabilities. Rather than immediately disclosing findings to vendors, some began selling this information to the highest bidders. This commercialisation created what is now known as the "vulnerability marketplace," where zero-days became valuable commodities.

Founded in 1998, iDefense was one of the first companies to offer bounties for vulnerabilities, establishing a formal program in 2002. By 2005, TippingPoint's Zero Day Initiative further legitimised the commercial aspect of vulnerability research by creating a structured program for purchasing zero-days from researchers and responsibly disclosing them to vendors.

Nation-States Enter the Game

The mid-2000s saw nation-states becoming significant players in the zero-day landscape as both defenders against and collectors of zero-day vulnerabilities. The discovery of Stuxnet in 2010 marked a watershed moment, revealing how advanced persistent threats (APTs) backed by nation-states could utilise multiple zero-day vulnerabilities in highly sophisticated attacks – demonstrating the immense resources governments were willing to invest in discovering and weaponising these vulnerabilities. The U.S. government also established the Vulnerability Equities Process in 2010 to determine whether to disclose or retain knowledge of zero-days, balancing national security interests against broader cybersecurity concerns.

The Ultimate Cyber Weakness

Zero-day vulnerabilities represent the apex of cybersecurity threats. By definition, these are software or hardware flaws unknown to the affected vendor and for which no patch exists. The term "zero-day" refers to the zero days defenders have had to develop countermeasures. These vulnerabilities are prized precisely because exploitation can occur before defenders have any opportunity to mitigate the risk.

What makes zero-days so potent is their guaranteed effectiveness against even well-defended targets. When organisations follow security best practices - keeping systems updated, implementing defence-in-depth strategies, and monitoring for known threats -zero days remain the one attack vector that could bypass these measures entirely. This is why they command such extraordinary prices in both legitimate and underground markets, with some high-impact zero-days selling for millions of dollars.

The 2010s witnessed several devastating zero-day exploitations that demonstrated their power:

• The Stuxnet malware targeting Iranian nuclear facilities exploited four separate zero-days, showing how nation-states could combine multiple unknown vulnerabilities into sophisticated attack chains.
• Operation Aurora in 2010 leveraged a zero-day in Internet Explorer to compromise Google and dozens of other major corporations, demonstrating how a single unknown vulnerability could enable widespread industrial espionage.
• The Equation Group (widely believed to be linked to the NSA) maintained an arsenal of zero-days that remained effective for years before discovery, illustrating how sophisticated actors could identify and weaponise vulnerabilities long before the security community became aware of them.

The power of zero-day vulnerabilities lies in their asymmetry - attackers need to find just one unknown vulnerability, while defenders must protect against all possible flaws. This fundamental imbalance ensures that despite advances in security technologies, zero-day vulnerabilities remain the most sought-after resource in the cyber offensive.

The Zero-Day Economy

Today's zero-day marketplace has evolved into a complex ecosystem with multiple participants:

1. Bug Bounty Programs: Companies like Google, Microsoft, and Apple offer substantial rewards for responsibly disclosed vulnerabilities, with some bounties exceeding $1 million for critical zero-days.
2. Vulnerability Brokers: Firms like Zerodium act as intermediaries, purchasing zero-days from researchers and selling them to clients, including governments.
3. Exploit Developers: Specialized teams convert vulnerability information into reliable exploit code.
4. Nation-State Actors: Government agencies maintain arsenals of zero-days for intelligence gathering, surveillance, and offensive cyber operations.
5. Cybercriminal Organisations: Criminal enterprises increasingly target zero-days for ransomware operations and data theft.

The financial incentives are substantial—in 2021, Zerodium advertised payouts of up to $2.5 million for Android zero-days and $2 million for iOS zero-click exploits.

Ethical Considerations and Responsible Disclosure

The discovery and handling of zero-day vulnerabilities raise profound ethical questions. Security researchers grapple with competing imperatives: the desire to protect users by disclosing vulnerabilities versus the potential for causing harm before patches are available.

Responsible disclosure protocols have evolved as a middle ground, with researchers typically providing vendors a 90-day window to develop patches before public disclosure. Google's Project Zero has been influential in standardizing this approach, though debates continue about appropriate timelines and exceptions.

The Future of Zero-Days

Looking ahead, several trends will shape the zero-day landscape:

AI and Automation: Machine learning is increasingly employed to discover vulnerabilities and defend against them. Automated vulnerability discovery tools can scan code at unprecedented speed and scale.

Supply Chain Vulnerabilities: As software ecosystems grow more complex, vulnerabilities in shared libraries and dependencies create cascading effects across multiple applications.

IoT Expansion: The proliferation of Internet of Things devices introduces new attack surfaces, often with limited security resources for ongoing patching.

Zero Trust Architecture: Organisations are moving toward security models that assume breaches will occur. These models limit the impact of zero-day exploits through compartmentalisation and strict access controls.

The Race Continues...

The history of zero-day vulnerabilities mirrors the evolution of our digital infrastructure, from isolated, academic curiosities to critical components of national security strategies and criminal enterprises. As our dependence on technology deepens, the discovery, disclosure, and mitigation of these vulnerabilities become more significant.

The zero-day ecosystem will continue to evolve, shaped by technological advances, economic incentives, regulatory frameworks, and ethical considerations. Understanding this landscape is essential for organisations, individuals, cybersecurity professionals, and anyone navigating our increasingly connected world.

The race between vulnerability discovery and remediation remains a defining feature of digital security, with profound implications for privacy, safety, and trust in our technological future.