Prioritizing Vulnerabilities with EPSS: Managing the CVE Flood
- [01] Security teams are overwhelmed by the increasing volume of vulnerability disclosures which has tripled over the last decade.
- [02] Enterprise vulnerability management workflows across all sectors are hindered by the volume of non-exploitable high-severity disclosures.
- [03] Organizations should adopt EPSS to prioritize remediation efforts based on the actual probability of exploitation rather than technical impact alone.
The Escalating Volume of Vulnerabilities
Security professionals face a daily influx of CVE entries that has grown exponentially over the last ten years. According to SANS ISC, the volume of reported vulnerabilities has surged from approximately 7,938 in 2014 to over 30,000 in 2024. This volume creates a massive backlog for any SOC or security engineering team attempting to maintain a patch-all policy. The sheer density of information makes it impossible to remediate every identified flaw, necessitating a shift from comprehensive patching to risk-based prioritization.
Traditionally, organizations have relied on CVSS scores to determine which vulnerabilities require immediate attention. While CVSS provides a measure of technical severity (the potential impact if an exploit occurs), it does not account for the real-world likelihood of that exploit being used in the wild. This gap often leads to teams patching vulnerabilities with high scores that have zero active exploitation while leaving lower-scored but actively exploited flaws unaddressed.
Understanding the Exploit Prediction Scoring System (EPSS)
The Exploit Prediction Scoring System (EPSS) is a data-driven effort aimed at solving this prioritization dilemma. Maintained by FIRST, EPSS provides a probability score indicating how likely a specific vulnerability is to be exploited within the next 30 days. This CVSS vs EPSS comparison guide highlights that while CVSS measures the ‘what’ (severity), EPSS measures the ‘when’ and ‘if’ (likelihood).
EPSS version 3 utilizes more than 1,000 features to calculate these probabilities. These features include technical attributes of the vulnerability, public discussions on social media, mentions in the MITRE ATT&CK framework, code availability on platforms like GitHub, and vendor-specific data. By synthesizing these signals, EPSS allows defenders to identify the small percentage of vulnerabilities—roughly 2% to 7%—that are actually targeted by threat actors. This focus significantly increases the efficiency of remediation programs, as teams can achieve higher risk reduction with fewer resources.
Implementing Exploit Prediction Scoring System in SOC Operations
When implementing Exploit Prediction Scoring System in SOC workflows, analysts should view it as a filter for their existing vulnerability scanners. A vulnerability with a high CVSS score but a low EPSS score might be deprioritized in favor of a medium CVSS score that shows a high EPSS percentile. For instance, an RCE vulnerability with no known exploit code and low attacker interest may have a lower EPSS score than a Privilege Escalation flaw that is actively being integrated into malware kits.
Security leaders can use EPSS to define thresholds. A common strategy involves prioritizing any CVE with an EPSS score above 0.1 (a 10% chance of exploitation in 30 days). This threshold-based approach helps teams avoid the ‘analysis paralysis’ that occurs when staring at thousands of critical alerts. This method is a core component of how to use EPSS for vulnerability prioritization, allowing for a measurable reduction in the mean time to remediate (MTTR) for high-risk assets.
Tactical Recommendations for Vulnerability Management
To move beyond reactive patching, organizations should integrate EPSS data directly into their vulnerability management tools. Most modern scanners and risk aggregators now support EPSS as a standard field. Defenders should also consider the following actions:
- Shift to Risk-Based Patching: Use EPSS to filter out the noise. If a vulnerability has a low probability of exploitation and requires complex local access, it should not supersede high-probability remote threats.
- Monitor Percentiles: EPSS provides both a probability score and a percentile. The percentile indicates how much more likely a CVE is to be exploited compared to all other known vulnerabilities. Focus on the 95th percentile and above.
- Review Legacy CVEs: The CVE flood includes many older vulnerabilities that may suddenly see renewed interest. Periodically re-scanning the environment for legacy flaws with rising EPSS scores can prevent breaches originating from forgotten technical debt.
By adopting these strategies, defenders can better manage the overwhelming volume of disclosures and ensure that limited remediation resources are applied where they will provide the most significant defensive benefit.
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