EPSS Score: Improving Vulnerability Prioritization in 2024

Nir Dagan, DevSecOps Engineer

August 27, 2024

When cloud security tools discover a sea of vulnerabilities, assessing and prioritizing them efficiently can mean the difference between drowning in alerts and getting breached, or squelching an attack before it happens. A robust security posture and effective vulnerability prioritization are most efficiently achieved with the Exploit Prediction Scoring System (EPSS). This handy guide will provide security practitioners with a comprehensive outline of the EPSS model, how it is calculated, its benefits, limitations, and how it compares to other scoring systems like the Common Vulnerability Scoring System (CVSS). EPSS can assist your organization in addressing its most critical vulnerabilities more efficiently if it is integrated into your existing risk assessment processes.

What is EPSS score?

An Exploit Prediction Scoring System (EPSS) predicts the likelihood that a vulnerability will be exploited within the next 30 days in the wild. By leveraging machine learning and historical exploit data, EPSS scores provide a data-driven approach to vulnerability prioritization developed by the Forum of Incident Response and Security Teams (FIRST). The secret sauce is that EPSS scores identify vulnerabilities that are most likely to be targeted by attackers, so organizations can prioritize efficiently and focus their remediation efforts there.

How are EPSS Scores Calculated?

EPSS scores are calculated using a combination of factors, including:

Historical Exploit Data: EPSS analyzes past exploit activity to identify patterns and trends;
Vulnerability Attributes: Considers characteristics such as CVSS scores, publication dates, and affected products;
Threat Intelligence: Integrates information from various threat intelligence sources to assess the current threat landscape;
Machine Learning Models: Utilizes advanced machine learning algorithms to predict the likelihood of exploitation based on the gathered data.

The resulting EPSS score ranges from 0 to 1, with higher scores indicating a greater probability of exploitation for that specific vulnerability.

The Benefits of Using EPSS Scores in Security Assessments

Improved Prioritization
Instead of focusing only on severity like other scores, EPSS scores help prioritize vulnerabilities based on the likelihood of exploitation. This allows security teams to focus on addressing the most imminent threats, thereby improving overall security posture.

Resource Optimization
By identifying which vulnerabilities are most likely to be exploited, organizations can allocate their resources more efficiently, reducing the time and effort spent on less critical issues.

Data-Driven Decisions
EPSS scores are derived from empirical data and advanced analytics, providing a reliable basis for decision-making in vulnerability management.

Enhanced Risk Management
Incorporating EPSS scores into risk assessments provides a more comprehensive view of the threat landscape, enabling better risk mitigation strategies.

EPSS Use Case
For example, if a vulnerability with a high CVSS score but a low EPSS score is identified, it may indicate that while the vulnerability is severe, it is less likely to be exploited in the near term. Conversely, a lower-severity vulnerability with a high EPSS score would warrant immediate attention due to its higher likelihood of being targeted by attackers. Using these models for enhanced prioritization ensures a comprehensive and cost-effective approach to vulnerability management and remediation.

The Limitations of the EPSS Score

Predictive Nature
While EPSS scores provide valuable insights, they are predictive and not deterministic. This means that while a high EPSS score indicates a higher likelihood of exploitation, it does not guarantee that the vulnerability will be exploited if not addressed.

Data Dependence
The accuracy of an EPSS score depends on the availability and quality of historical exploit data and threat intelligence. Gaps in data can affect the score's reliability.

Best Used as a Complementary Tool
EPSS should be used as a complementary tool alongside other risk assessment methodologies. Relying solely on EPSS without considering other factors, such as business impact and compliance requirements, can result in incomplete risk assessments.

Comparing EPSS vs. CVSS

Feature	EPSS	CVSS
Focus	Likelihood of exploitation	Severity of vulnerability
Scoring Range	0 to 1	0 to 10
Data Utilized	Historical exploit data, threat intelligence	Vulnerability attributes, impact, and severity
Purpose	Prioritizing based on exploit likelihood	Assessing severity and impact
Update Frequency	Regularly based on new data	Periodically, typically with new CVE entries
Primary Use	Dynamic risk assessment	Initial risk assessment and impact analysis

How to Use EPSS Scores: A Short Guide

Easily Integrating EPSS into Existing Risk Assessment Processes

Gather Vulnerability Data: Collect data on vulnerabilities from your existing security tools and databases.
Calculate EPSS Scores: Use the EPSS framework to obtain scores for each identified vulnerability.
Prioritize Vulnerabilities: Rank vulnerabilities based on their EPSS scores, focusing on those with the highest likelihood of exploitation.
Develop Remediation Plans: Create targeted remediation plans for high-priority vulnerabilities, ensuring timely and effective mitigation.
Monitor and Update: Continuously monitor EPSS scores and update your prioritization and remediation efforts as new data becomes available.

How Opus Can Help Maximize the Benefits of EPSS

1. Data Aggregation
With Opus, security and development teams already have continuously-updated vulnerability data from various security tools and public databases, including EPSS scores. Once EPSS is integrated into the Opus platform, Opus uses this data to provide a comprehensive view of vulnerabilities across your entire ecosystem.

2. Prioritization
Opus uses EPSS scores to prioritize vulnerabilities based on their likelihood of exploitation. This ensures that vulnerabilities with a higher risk of being exploited are addressed first. The prioritization process in Opus considers:

Historical Exploit Data: Information on past exploit activity helps determine the current risk level.
Threat Intelligence: Insights from various threat intelligence sources enrich the understanding of each vulnerability's threat landscape.
Environmental Context: Factors such as the criticality of affected assets, compliance requirements, and existing mitigating controls are taken into account.

3. Enhanced Risk Assessment

Through EPSS scores, Opus can provide a more accurate risk assessment. This allows security teams to optimize resource allocation and improve overall security posture by focusing on vulnerabilities that pose the greatest threats.

4. Automated Workflows
Opus automates the remediation process by creating automated workflows that prioritize vulnerabilities based on EPSS scores. These workflows include:

Alerting and Notification: Security teams are alerted to high-risk vulnerabilities identified by their EPSS scores.
Ticketing and Task Assignment: Vulnerabilities are automatically assigned to the relevant teams for remediation.
Progress Tracking: The platform tracks the progress of remediation efforts, ensuring that high-priority vulnerabilities are addressed promptly.

5. Reporting and Dashboards
Opus provides detailed reports and dashboards that include EPSS scores. These visualizations help stakeholders understand the risk landscape and the effectiveness of their vulnerability management efforts. Key features include:

SLA Tracking: Monitoring of Service Level Agreement (SLA) compliance based on vulnerability priorities.
Comparative Analysis: Insights into how different teams and services are performing in terms of vulnerability remediation.
Zero-Day Response: Quick identification and response to newly discovered vulnerabilities with high EPSS scores.

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FAQ

How accurate are EPSS scores?

EPSS scores are based on empirical data and advanced analytics, making them highly reliable for predicting the likelihood of exploitation. However, they are not deterministic and should be used alongside other risk assessment tools.

How often are EPSS scores updated?

EPSS scores are regularly updated as new data becomes available, ensuring that they reflect the most current threat landscape.

How do I find the EPSS score of a specific vulnerability?

EPSS scores for specific vulnerabilities can be found on the FIRST EPSS website or integrated into your vulnerability management tools. EPSS scores can also be found in the Opus Security platform, which integrates EPSS data and provides a comprehensive view of each vulnerability's risk profile.

Can EPSS scores be integrated into existing risk assessment processes?

Yes, EPSS scores can be integrated into existing risk assessment processes. Opus Security makes this integration seamless, allowing organizations to incorporate EPSS scores into their vulnerability prioritization workflows.

How does Opus use EPSS scores in its platform?

Opus integrates EPSS scores to prioritize vulnerabilities based on their likelihood of exploitation. This helps in focusing remediation efforts on the most critical vulnerabilities, enhancing overall security posture.

What benefits do EPSS scores offer over traditional scoring methods like CVSS?

EPSS scores offer dynamic, real-time insights into the likelihood of exploitation, whereas CVSS scores provide a static assessment of a vulnerability's severity. Using EPSS scores allows for more proactive and effective vulnerability management.

Can EPSS scores help with compliance requirements?

Yes, EPSS scores can assist with compliance by ensuring that high-risk vulnerabilities are prioritized and remediated promptly, helping organizations meet regulatory standards.

How does Opus handle vulnerabilities with no EPSS score?

Opus prioritizes vulnerabilities without an EPSS score using other risk assessment methods, such as CVSS scores and internal threat intelligence.

Can I customize how EPSS scores are used in Opus?

Yes, Opus allows customization of how EPSS scores are weighted and used in vulnerability prioritization, ensuring that the system aligns with your organization's specific risk management needs.

How does Opus ensure the data from EPSS is reliable?

Opus integrates EPSS scores from trusted sources and continually updates its data to ensure reliability. The platform also provides context and intelligence around each score to support informed decision-making.

What kind of organizations benefit the most from using EPSS scores?

Organizations with complex IT environments and those facing a high volume of vulnerabilities benefit the most from using EPSS scores, as it helps them efficiently prioritize and address the most critical risks.

How do EPSS scores compare to traditional vulnerability scanning results?

EPSS scores complement traditional vulnerability scanning by providing a probability-based assessment of exploitation risk, while traditional scans identify the presence and severity of vulnerabilities. Together, they offer a comprehensive risk management approach.

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Summary

Based on the likelihood of exploitation, the EPSS score is an effective tool for prioritizing vulnerabilities. With EPSS integrated into your existing risk assessment processes, your organization can more effectively address its most critical vulnerabilities. By providing a comprehensive platform for unified vulnerability management, Opus Security further enhances these benefits, ensuring a robust and proactive security posture.

For more information on end-to-end remediation orchestration, Discover how Opus Security streamlines complex remediation processes with automated ownership identification and flexible, no-code automation, enhancing overall risk management and response capabilities.

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