About EPSS, The Exploit Prediction Scoring System
Understanding EPSS for Better Vulnerability Management Lifecycle
With the increasing number of vulnerabilities being discovered security teams are challenged with prioritizing which vulnerabilities to address first. The Exploit Prediction Scoring System (EPSS) is designed to help cybersecurity professionals manage vulnerabilities based on the likelihood of exploitation, giving them an edge in their work.
We’ll explore EPSS, compare it to traditional vulnerability management tools like CVSS, explore its practical applications, and highlight why it should become a cornerstone of any organization’s vulnerability management strategy.
The Exploit Prediction Scoring System (EPSS) is a predictive analytics tool that assesses the probability that a specific vulnerability will be exploited in the next 30 days. Unlike traditional vulnerability scoring systems that focus on the severity of the vulnerability, EPSS is purely risk-based. It helps cybersecurity teams prioritize the vulnerabilities that are most likely to be exploited in real-world attacks, which is a critical capability when organizations are overwhelmed by thousands of potential threats.
The key idea behind EPSS is to close the gap between knowing which vulnerabilities exist and understanding which ones pose a coming threat. EPSS enables more targeted security efforts by focusing on exploitation likelihood rather than severity alone.
EPSS vs. CVSS?
The Common Vulnerability Scoring System (CVSS) has long been the industry standard for scoring vulnerabilities. It uses a 0-10 scale to represent the severity of a vulnerability. CVSS is effective for understanding the technical impact of a vulnerability, but it falls short when it comes to predicting which vulnerabilities are likely to be exploited.
Here’s a critical distinction: CVSS tells you how bad a vulnerability can be if exploited, but it doesn't tell you whether it’s likely to be exploited at all. This is an important gap in the vulnerability management lifecycle because patching every high-severity vulnerability (CVSS score of 9 or above) can result in wasted effort on vulnerabilities that are unlikely to be exploited.
EPSS, on the other hand, calculates the probability of exploitation. This predictive focus allows network defenders to prioritize their patching efforts more effectively, addressing vulnerabilities that are both severe and likely to be exploited in the near term.
Using Real-World Exploit Data
The strength of EPSS lies in its data-driven approach. EPSS is built on years of exploit data gathered from a range of sources, including sensors, honeypots, and intrusion detection systems deployed globally. This real-world data informs EPSS’s predictive model, allowing it to assess the likelihood of exploitation based on historical patterns and active attack trends.
However, EPSS is not without its blind spots. Sectors such as IoT, healthcare, and industrial systems often have limited visibility in the dataset due to a lack of exploit reporting. This is a recognized challenge, and the EPSS team is continually working to expand its data sources and improve the system’s accuracy across more specialized areas.
How EPSS Works
EPSS provides a score between 0 and 1, representing the likelihood that a given vulnerability will be exploited within the next 30 days. Organizations can access these scores for free, either by downloading them as a CSV file or by integrating them into their systems via an API. This accessibility ensures that organizations of any size can take advantage of EPSS’s predictive power.Whether you’re assessing a single server or an entire global network, EPSS can help prioritize vulnerabilities based on exploitation risk.
Exploited Vulnerabilities
One of the more fascinating insights from EPSS data is the age of vulnerabilities being exploited today. Contrary to popular belief, many of the vulnerabilities being actively exploited are not new. In fact, two-thirds of vulnerabilities that are currently being exploited are more than five years old, and a third are over ten years old.
This reveals a critical weakness in vulnerability management practices across many organizations. While security teams may focus heavily on patching newly discovered vulnerabilities, they often overlook older ones that are still exploitable. EPSS provides an opportunity to address this gap by highlighting vulnerabilities that may have been neglected for years but still pose a significant risk.
How can organizations use EPSS to improve their security posture?
I am adding a few practical examples that we can use in your organizations.
You can prioritize patching effort: Rather than patching every high-severity vulnerability, security teams can use EPSS scores to focus on severe and likely exploited vulnerabilities.
Implement Security Metrics and Reporting Using EPSS: EPSS scores can be used to track the risk profile of different applications or infrastructure components, allowing for more granular risk assessments and better reporting to stakeholders.
Run Historical Analysis: EPSS allows organizations to track the likelihood of exploitation over time, providing valuable insights into long-term vulnerability management trends.
If your organization hasn’t yet integrated EPSS into its vulnerability management process, EPSS can help streamline your patching efforts, reduce your attack surface, and improve your overall security posture.
Conclusion
The Exploit Prediction Scoring System (EPSS) represents a significant advancement in vulnerability management. It offers a much-needed focus on the likelihood of exploitation rather than just the severity of vulnerabilities. By prioritizing vulnerabilities based on real-world data, EPSS helps organizations save time, effort, and resources while focusing their efforts where they are needed most.
Implementing EPSS into your organization’s vulnerability management strategy would be a smart move that can lead to more effective patching and better security outcomes. And as the system continues to evolve and improve, it will only become a more valuable tool in the fight against cyber threats.