Network Vulnerability Exposure Calculator

Quantifies your network's vulnerability exposure by combining asset value, threat likelihood, vulnerability severity (CVSS-based), and control effectiveness into a single actionable risk score.

Relative importance of the asset to the organization.
Probability that a threat actor will attempt to exploit the vulnerability.
Common Vulnerability Scoring System base score for the vulnerability.
Effectiveness of existing security controls (patches, WAF, IDS, segmentation, etc.).
Number of days the vulnerability has been unpatched / exposed.

Formula

Step 1 – Normalize CVSS:
CVSS_norm = CVSS_Base_Score / 10

Step 2 – Residual Vulnerability:
RV = CVSS_norm × (1 − Control_Effectiveness)
Represents how much of the raw vulnerability survives after controls are applied.

Step 3 – Temporal Factor (logarithmic):
TF = ln(Exposure_Window_days + 1) / ln(366), capped at 1
Models diminishing marginal risk increase over time; reaches ~1 at one year.

Step 4 – Raw NVE:
NVE_raw = Asset_Value × Threat_Likelihood × RV × (1 + TF)

Step 5 – Normalize to 0–10 scale:
NVE = (NVE_raw / 20) × 10
Maximum theoretical raw value = 10 × 1 × 1 × 2 = 20.

Risk Bands: Minimal < 2 | Low 2–4 | Moderate 4–6 | High 6–8 | Critical ≥ 8

Assumptions & References

  • CVSS Base Scores are sourced from the NIST National Vulnerability Database (NVD) or your internal scanner (Nessus, Qualys, OpenVAS).
  • Threat Likelihood should be estimated using threat-intelligence feeds, historical incident data, or the MITRE ATT&CK framework.
  • Control Effectiveness is a composite score reflecting patch status, network segmentation, IDS/IPS coverage, WAF deployment, and access controls (0 = none, 1 = fully mitigated).
  • The logarithmic temporal factor is inspired by CVSS Temporal metrics and reflects that unpatched vulnerabilities attract increasing attacker attention over time, but with diminishing marginal increase.
  • Asset Value should align with your organization's Business Impact Analysis (BIA) or data classification policy.
  • This model is aligned with NIST Cybersecurity Framework risk assessment guidance (SP 800-30 Rev. 1).
  • NVE is a relative scoring tool. Absolute thresholds should be calibrated to your organization's risk appetite.
  • CVSS v3.1 is assumed; CVSS v4.0 scores are also compatible as both use a 0–10 scale.

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