Cyber threats are evolving faster than ever – and even the best defenses can be caught off guard. Some of the most dangerous attacks happen before software vendors even know a vulnerability exists. These are known as zero-day vulnerabilities, and they represent one of the most urgent challenges for modern cybersecurity teams.
Zero-day exploits have increased by 141% in the last five years,1 with 75 zero-day vulnerabilities actively exploited during 2024 alone.2 Read on to learn why zero-day vulnerabilities matter, how a zero-day attack can occur, and what strategies your organization can use to prevent them.
What Is a Zero-Day Vulnerability?
A zero-day vulnerability is a security flaw in a piece of software, firmware, or hardware that isn’t known to the vendor or the general public. The developer hasn't created a patch or update to fix it yet, so attackers can exploit it without warning. The term "zero-day" refers to the fact that the vendor has had zero days to prepare a fix before an attack begins.
These vulnerabilities can hide in almost anything: operating systems, web browsers, network appliances that protect your infrastructure, or even the IoT devices connected throughout your organization. Once attackers discover one of these flaws, they can use it to access sensitive systems or data before your defenses are even aware of the problem.
Zero-Day Exploit vs. Zero-Day Attack
Although they’re often used interchangeably, a zero-day exploit and a zero-day attack refer to two different parts of the same process.
- Zero-Day Exploit: A zero-day exploit is the code hackers develop to take advantage of a zero-day vulnerability.
- Zero-Day Attack: A zero-day attack is the actual execution and deployment of that exploit in the real world.
For example, an attacker might discover a flaw in a web browser’s code. The exploit would be the script or malware designed to use that flaw to bypass security controls, while the attack would be the deployment of that code to infect real-world targets.
Zero-day exploits are extremely valuable in the cybercrime world – often sold on the dark web or used by nation-state groups to target specific industries or government agencies.
How Does a Zero-Day Attack Work?
A typical zero-day attack follows a predictable pattern, even if the specifics vary depending on the vulnerability and target.
Discovery
A cybercriminal or security researcher uncovers a previously unknown flaw in a piece of software or device.
Exploit Creation
The attacker develops a payload – a zero-day exploit – to take advantage of that vulnerability.
Attack Execution
The attacker uses the exploit to breach the system and deploy malware or access data and infrastructure.
Vendor Response
Once the business detects and reports the attack, the vendor should begin developing and releasing a patch.
Public Disclosure
After a fix is available, details of the vulnerability are often shared publicly to encourage users to update their systems.
Real-World Examples of Zero-Day Vulnerabilities
Zero-day vulnerabilities have impacted some of the most widely used software in the world. Here are a few notable examples:
- SharePoint Attacks: Hackers exploited a pair of zero‑day vulnerabilities, referred to as “ToolShell,” against on‑prem SharePoint servers in July 2025. Attackers were able to use these flaws to access sensitive data and move laterally in affected environments before patches were available.3
- React2Shell Vulnerability: A zero‑day vulnerability was discovered in React Server Components and confirmed to be exploited by multiple threat actors in December 2025. React2Shell scored at the highest risk level, impacting many web apps built on the React framework.4
- SonicWall Appliances: Also in December 2025, attackers exploited a local privilege escalation zero‑day vulnerability in SonicWall SMA 1000 appliances. This flaw allowed attackers to elevate privileges and access infrastructure remotely before a patch was released.5
These examples show why zero-day protection must be a proactive effort – not a reactive one.
What Are the Dangers of a Zero-Day Vulnerability?
Zero-day attacks are especially difficult to defend against because traditional security tools rely on known threat signatures or past attack patterns. With a brand-new exploit, there’s no preexisting rule or update that can detect it.
The result is a blind spot in your defense posture that can be exploited even if your software and antivirus appear fully updated. That’s why network security management, firewall configuration best practices, and threat intelligence are all essential parts of a zero-day prevention strategy.
7 Ways To Prevent Zero-Day Attacks
While it’s impossible to eliminate zero-day risk completely, there are proven strategies to reduce your exposure and respond faster when new threats appear.
1. Implement Layered Security
A single tool can’t stop every threat. Use multiple layers of defense – including next-generation firewalls, endpoint detection and response (EDR), and SIEM services – to detect anomalies across your environment.
At Aseva, we design layered cybersecurity frameworks that combine network, cloud, and endpoint protection under one unified system.
2. Keep Software and Firmware Updated
Updates won't protect you against zero-day flaws that haven't been discovered yet, but they eliminate the large category of vulnerabilities that attackers actively exploit because they're easy targets.
Establish a strict patch management policy in your organization and prioritize critical updates as soon as your vendor releases them.
3. Use Threat Intelligence and Behavioral Analytics
AI-powered security tools can identify suspicious behavior even without knowing an attack’s specific signature. Behavioral detection systems monitor traffic patterns flowing through your network, user activity on systems, and logs from your endpoints to spot potential zero-day exploits in real time.
4. Conduct Regular Penetration Testing
Simulated attacks can reveal vulnerabilities before attackers find them. Penetration testing, combined with continuous vulnerability management, helps identify and remediate weaknesses early.
Aseva’s vulnerability management as a service (VMaaS) and penetration testing solutions provide this proactive visibility – helping you discover hidden flaws before they become entry points.
5. Enforce Network Segmentation
Separating your critical systems from less sensitive parts of your network helps limit the impact of a breach. Even if an attacker accesses your network via a zero-day exploit, segmentation prevents them from moving freely throughout your entire infrastructure.
6. Train Employees on Cyber Awareness
Phishing is still one of the most common ways attackers deliver zero-day payloads to organizations. Providing regular security awareness training to your employees can help them recognize suspicious links, dangerous attachments, and behavior that doesn't seem right.
7. Partner With a Managed Security Provider
Preventing zero-day vulnerabilities requires around-the-clock monitoring, rapid patch deployment, and advanced threat intelligence. For most businesses, this level of oversight is difficult to maintain in-house.
That’s why many organizations partner with a managed security provider like Aseva. Our team detects and blocks threats using Fortinet’s advanced security platforms – supported by human expertise and strategic guidance.
Stay Ahead of Zero-Day Threats With Aseva
Zero-day vulnerabilities are a serious risk, but they don’t have to leave your organization exposed. With the right mix of technology and support, you can limit their impact and detect them sooner.
At Aseva, we know that zero-day attacks can strike even the most secure networks. That’s why we combine cybersecurity solutions like proactive monitoring, managed threat detection, and incident response to keep our clients protected at all times. We stay ahead of evolving attacks so you don't have to.
Ready to reduce your exposure to zero-day exploits? Get started with Aseva today.
Sources:
- https://zeronetworks.com/blog/what-is-a-zero-day-attack-everything-you-need-to-know
- https://thehackernews.com/2025/04/google-reports-75-zero-days-exploited.html
- https://www.washingtonpost.com/technology/2025/07/20/microsoft-sharepoint-hack
- https://cloud.google.com/blog/topics/threat-intelligence/threat-actors-exploit-react2shell-cve-2025-55182
- https://www.helpnetsecurity.com/2025/12/17/sonicwall-cve-2025-40602
