performing-cve-prioritization-with-kev-catalog

Leverage the CISA Known Exploited Vulnerabilities catalog alongside EPSS and CVSS to prioritize CVE remediation based on real-world exploitation evidence.

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Repository: braydos-h/BreachPilot
Last source activity: August 24, 2026 at 12:22
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name	performing-cve-prioritization-with-kev-catalog
description	Leverage the CISA Known Exploited Vulnerabilities catalog alongside EPSS and CVSS to prioritize CVE remediation based on real-world exploitation evidence.
domain	cybersecurity
subdomain	vulnerability-management
tags	["cisa-kev","cve","vulnerability-prioritization","epss","bod-22-01","threat-intelligence","remediation"]
version	1.0
author	mahipal
license	Apache-2.0
nist_ai_rmf	["MEASURE-2.7","MAP-5.1","MANAGE-2.4"]
atlas_techniques	["AML.T0070","AML.T0066","AML.T0082"]
nist_csf	["ID.RA-01","ID.RA-02","ID.IM-02","ID.RA-06"]
mitre_attack	["T1190","T1203","T1068"]

Performing CVE Prioritization with KEV Catalog

Overview

The CISA Known Exploited Vulnerabilities (KEV) catalog, established through Binding Operational Directive (BOD) 22-01, is a living list of CVEs that have been actively exploited in the wild and carry significant risk. As of early 2026, the catalog contains over 1,484 entries, growing 20% in 2025 alone with 245 new additions. This skill covers integrating the KEV catalog into vulnerability prioritization workflows alongside EPSS (Exploit Prediction Scoring System) and CVSS to create a risk-based approach that prioritizes vulnerabilities with confirmed exploitation activity over theoretical severity alone.

When to Use

When conducting security assessments that involve performing cve prioritization with kev catalog
When following incident response procedures for related security events
When performing scheduled security testing or auditing activities
When validating security controls through hands-on testing

Prerequisites

Access to vulnerability scan results (Qualys, Nessus, Rapid7, etc.)
Familiarity with CVE identifiers and NVD
Understanding of CVSS scoring (v3.1 and v4.0)
API access to CISA KEV, EPSS, and NVD endpoints
Python 3.8+ with requests and pandas libraries

Core Concepts

CISA KEV Catalog Structure

Each KEV entry contains:

CVE ID: The CVE identifier (e.g., CVE-2024-3094)
Vendor/Project: Affected vendor and product name
Vulnerability Name: Short description of the vulnerability
Date Added: When CISA added it to the catalog
Short Description: Brief technical description
Required Action: Recommended remediation action
Due Date: Deadline for federal agencies (FCEB) to remediate
Known Ransomware Campaign Use: Whether ransomware groups exploit it

BOD 22-01 Remediation Timelines

CVE Publication Date	Remediation Deadline
2021 or later	2 weeks from KEV listing
Before 2021	6 months from KEV listing

Multi-Factor Prioritization Model

Factor	Weight	Data Source

KEV Listed	EPSS > 0.5	CVSS >= 9.0	Priority	SLA
Yes	Any	Any	P1-Emergency	48 hours
No	Yes	Yes	P1-Emergency	48 hours
No	Yes	No	P2-Critical	7 days
No	No	Yes	P2-Critical	7 days
No	No	No (>= 7.0)	P3-High	14 days
No	No	No (>= 4.0)	P4-Medium	30 days
No	No	No (< 4.0)	P5-Low	90 days

import requests
import json
from datetime import datetime

KEV_URL = "https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json"


def fetch_kev_catalog():
    """Download and parse the CISA KEV catalog."""
    response = requests.get(KEV_URL, timeout=30)
    response.raise_for_status()
    data = response.json()

    catalog = {}
    for vuln in data.get("vulnerabilities", []):
        cve_id = vuln["cveID"]
        catalog[cve_id] = {
            "vendor": vuln.get("vendorProject", ""),
            "product": vuln.get("product", ""),
            "name": vuln.get("vulnerabilityName", ""),
            "date_added": vuln.get("dateAdded", ""),
            "description": vuln.get("shortDescription", ""),
            "action": vuln.get("requiredAction", ""),
            "due_date": vuln.get("dueDate", ""),
            "ransomware_use": vuln.get("knownRansomwareCampaignUse", "Unknown"),
        }

    print(f"[+] Loaded {len(catalog)} CVEs from CISA KEV catalog")
    print(f"    Catalog version: {data.get('catalogVersion', 'N/A')}")
    print(f"    Last updated: {data.get('dateReleased', 'N/A')}")
    return catalog


kev = fetch_kev_catalog()

EPSS_API = "https://api.first.org/data/v1/epss"


def get_epss_scores(cve_list):
    """Fetch EPSS scores for a batch of CVEs."""
    scores = {}
    batch_size = 100
    for i in range(0, len(cve_list), batch_size):
        batch = cve_list[i : i + batch_size]
        cve_param = ",".join(batch)
        response = requests.get(EPSS_API, params={"cve": cve_param}, timeout=30)
        if response.status_code == 200:
            for entry in response.json().get("data", []):
                scores[entry["cve"]] = {
                    "epss": float(entry.get("epss", 0)),
                    "percentile": float(entry.get("percentile", 0)),
                }
    return scores

import pandas as pd


def prioritize_vulnerabilities(scan_results, kev_catalog, epss_scores):
    """Apply multi-factor prioritization to scan results."""
    prioritized = []

    for vuln in scan_results:
        cve_id = vuln.get("cve_id", "")
        cvss_score = float(vuln.get("cvss_score", 0))
        asset_criticality = float(vuln.get("asset_criticality", 3))
        exposure = float(vuln.get("network_exposure", 3))

        in_kev = cve_id in kev_catalog
        kev_data = kev_catalog.get(cve_id, {})
        epss_data = epss_scores.get(cve_id, {"epss": 0, "percentile": 0})
        epss_score = epss_data["epss"]

        # Composite risk score calculation
        risk_score = (
            (1.0 if in_kev else 0.0) * 10 * 0.30
            + epss_score * 10 * 0.25
            + cvss_score * 0.20
            + (asset_criticality / 5.0) * 10 * 0.15
            + (exposure / 5.0) * 10 * 0.10
        )

        # Assign priority level
        if in_kev or (epss_score > 0.5 and cvss_score >= 9.0):
            priority = "P1-Emergency"
            sla_days = 2
        elif epss_score > 0.5 or cvss_score >= 9.0:
            priority = "P2-Critical"
            sla_days = 7
        elif cvss_score >= 7.0:
            priority = "P3-High"
            sla_days = 14
        elif cvss_score >= 4.0:
            priority = "P4-Medium"
            sla_days = 30
        else:
            priority = "P5-Low"
            sla_days = 90

        prioritized.append(
            {
                "cve_id": cve_id,
                "cvss_score": cvss_score,
                "epss_score": round(epss_score, 4),
                "epss_percentile": round(epss_data["percentile"], 4),
                "in_cisa_kev": in_kev,
                "ransomware_use": kev_data.get("ransomware_use", "N/A"),
                "kev_due_date": kev_data.get("due_date", "N/A"),
                "risk_score": round(risk_score, 2),
                "priority": priority,
                "sla_days": sla_days,
                "asset": vuln.get("asset", ""),
                "asset_criticality": asset_criticality,
            }
        )

    df = pd.DataFrame(prioritized)
    df = df.sort_values("risk_score", ascending=False)
    return df

def generate_report(df, output_file="kev_prioritized_report.csv"):
    """Generate summary report from prioritized vulnerabilities."""
    print("\n" + "=" * 70)
    print("VULNERABILITY PRIORITIZATION REPORT - KEV + EPSS + CVSS")
    print("=" * 70)

    print(f"\nTotal vulnerabilities analyzed: {len(df)}")
    print(f"KEV-listed vulnerabilities:    {df['in_cisa_kev'].sum()}")
    print(f"Ransomware-associated:         {(df['ransomware_use'] == 'Known').sum()}")

    print("\nPriority Distribution:")
    print(df["priority"].value_counts().to_string())

    print("\nTop 15 Highest Risk Vulnerabilities:")
    top = df.head(15)[["cve_id", "cvss_score", "epss_score", "in_cisa_kev", "risk_score", "priority"]]
    print(top.to_string(index=False))

    df.to_csv(output_file, index=False)
    print(f"\n[+] Full report saved to: {output_file}")