Combining CVSS and EPSS to prioritize vulnerability

Pallavi Vishwakarma
July 4, 2023

CVSS (Common Vulnerability Scoring System) and EPSS (Enterprise Priority Score System) are two methods for prioritizing vulnerabilities in an IT environment. EPSS takes into account the environment and assets of an organization, while CVSS assigns a numerical score based on the severity of a vulnerability. Combining CVSS and EPSS can give a complete picture of the importance of vulnerability, taking into account its technical severity and the particular effects it might have on the company. Organizations can more efficiently allocate resources and prioritize their vulnerability management efforts by combining these two approaches.

Combining CVSS with EPSS allows for the adjustment of priority based on variables including the criticality of the impacted systems, the possibility of exploitation, and the possible impact on the organization. The CVSS score can be used as a benchmark for the severity of a vulnerability. If a vulnerability affects a non-critical system that is difficult to access, for instance, it might be given a low priority even when it has a high CVSS score. In contrast, if a vulnerability impacts a vital system that is easily accessible, it might be given a greater priority. By taking both CVSS and EPSS into consideration, organizations can have a more informed and comprehensive view of the risk posed by a vulnerability and make more informed decisions on how to prioritize and manage that risk.

Following steps, organizations can take to combine CVSS and EPSS to prioritize their vulnerability

  1. Assign CVSS scores: Based on the severity, exploitability, and effect of each vulnerability, use the CVSS standard to assign a numerical score to each one.
  2. Establish EPSS criteria: Specify the EPSS criteria, including the criticality of the impacted systems, the possibility of exploitation, and the possible impact on the organization.
  3. Assign EPSS weights: Based on the organization's priorities and risk tolerance, assign a weight to each of the EPSS criteria.
  4. Calculate EPSS scores: Calculate EPSS scores by multiplying the CVSS score by the weighted EPSS criterion for each vulnerability.
  5. Prioritize Vulnerability: Determine which vulnerabilities need to be handled right now and which ones may be fixed with a lower priority by using the combined CVSS and EPSS scores to prioritize issues.
  6. Review and update: To make sure the CVSS and EPSS scores and criteria are current and accurate, review and update them on a regular basis.
  7. Apply remediation: Use the prioritized list of vulnerabilities to direct the application of corrective actions, such as patching systems, putting in place security measures, or taking other steps to lessen the risk that the vulnerabilities offer.

Following these steps can help organizations prioritize vulnerabilities and more efficiently spend resources to reduce risk.

What thinks organizations must keep in mind while implementing this method into their system

It's critical to have clear policies and procedures in place for managing vulnerabilities after they have been identified. This could involve routine scans and assessments to find new vulnerabilities, patch management procedures to quickly install updates, and incident response strategies to deal with successful vulnerability exploitation.

Effective vulnerability management requires a multi-faceted approach that includes both technical and organizational elements. This entails putting the appropriate people, processes, and policies in place to make sure that vulnerabilities are managed quickly and effectively, as well as the appropriate tools and technology in place to discover and prioritize vulnerabilities.

Organizations should also think about their general security posture and work to continually enhance it. Regular security assessments, employee security training, and proactive threat hunting to find and address potential security threats are some examples of this. Organizations can better safeguard themselves against the danger posed by vulnerabilities and assure the ongoing security of their systems and data by adopting a holistic approach to security.

Importance of using a combination of CVSS and EPSS to prioritize vulnerability

The combination of CVSS and EPSS is important for several reasons:

  • Better risk assessment: By considering both CVSS and EPSS scores organizations can have a more comprehensive idea about the risk posed by a vulnerability.
  • Improved resource allocation: By using this method organizations can allocate resources more effectively to address only the most critical vulnerability first.
  • Enhance security posture: By having a proper method in place for prioritizing vulnerability can help organizations to strengthen their security posture.
  • Increased efficiency: By having a systematic approach organizations can save lots of time in handling vulnerabilities that are low-priority. 
  • Compliance: Organizations must prioritize vulnerabilities and promptly address them in order to comply with some requirements, such as PCI DSS. The integration of CVSS and EPSS offers a framework for methodically and systematically satisfying these needs.

Final Thoughts

In order to prioritize vulnerabilities, it's crucial to keep in mind that combining CVSS with EPSS is just one approach that may not work for all businesses. In order to guarantee that the EPSS weightings and score system appropriately represent the organization's current threat environment and priorities, it is also crucial to review and update it on a regular basis. 

Additionally, while CVSS and EPSS offer useful data for prioritizing vulnerabilities, they shouldn't be used as the only criteria. It's also important to take into account other elements including the existence of mitigating controls, the accessibility of fixes or workarounds, and the degree of continuous exploitation in the wild.

In conclusion, combining CVSS and EPSS can give a more thorough and accurate picture of the priority of a vulnerability, but it should be used in conjunction with other variables and routinely examined to guarantee its continuous relevance. An effective vulnerability management program should include multiple methods for prioritizing vulnerabilities and a regular process for review and update.

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