The 4x4 Risk Matrix
The verdictFormula in the Risksheet implements a 4x4 lookup matrix. Impact levels form the rows; feasibility levels form the columns.
| Impact \ Feasibility | Very Low | Low | Medium | High |
|---|
| Severe | 3 | 4 | 5 | 5 |
| Major | 2 | 3 | 4 | 5 |
| Moderate | 1 | 2 | 3 | 4 |
| Negligible | 1 | 1 | 1 | 1 |
Verdict Scale Interpretation
| Verdict | Risk Level | Action Required |
|---|
| 1 | Negligible | No action needed. Risk is acceptable as-is. |
| 2 | Low | Acceptable. Monitor during lifecycle. |
| 3 | Medium | Investigation required. Consider risk reduction or provide documented justification for acceptance. |
| 4 | High | Unacceptable. Risk controls are mandatory. A Cybersecurity Goal with appropriate CAL must be defined. |
| 5 | Critical | Unacceptable. Immediate action required. Highest CAL (CAL 4) mandatory. |
Regardless of how feasible an attack is, if the damage impact is negligible, the verdict is always 1. This reflects the ISO/SAE 21434 principle that risk treatment prioritizes actual harm potential.
verdictFormula in the Risksheet configuration is a JavaScript function that:
- Reads the
taraImpact field (severe, major, moderate, negligible)
- Reads the
taraFeasibility field (high, medium, low, veryLow)
- Looks up the intersection in the 4x4 matrix
- Writes the integer result to
taraVerdict
Both inputs must be present for the formula to compute a result. If either taraImpact or taraFeasibility is empty, taraVerdict remains blank.
Visual Indicators
The verdictDecorator applies a five-color gradient to the Verdict column:
| Verdict | Color | Hex |
|---|
| 1 | Green | #4CAF50 |
| 2 | Light Green | #8BC34A |
| 3 | Amber | #FF9800 |
| 4 | Red | #f44336 |
| 5 | Dark Red | #b71c1c |
rowHeaderVerdict decorator extends this coloring to the row header, making the entire left edge of each row reflect its verdict level. This creates a heatmap effect visible even when scrolling horizontally through the Risksheet.
Verdict Drives CAL Requirements
The verdict score determines the minimum Cybersecurity Assurance Level (CAL) required for the linked Cybersecurity Goal. The calDecorator enforces this mapping:
| Verdict | Minimum CAL |
|---|
| 5 | CAL 4 |
| 4 | CAL 3 |
| 3 | CAL 2 |
| 1 — 2 | CAL 1 |
Verdict in Reports and Dashboards
The verdict score flows into two key dashboards:
- TARA Summary Report — Aggregates verdicts across all TARA modules into V1—V5 distribution cards. Conditional alert banners highlight modules with unacceptable risk (V4/V5).
- Cybersecurity Case — Uses verdicts to determine case status: OPEN if any V4/V5 records remain, READY FOR REVIEW when all risks are at acceptable levels.
Design Rationale
The 4x4 matrix is deliberately asymmetric. Severe-impact threats receive a verdict of 3 even at Very Low feasibility, because the consequences of a successful attack on safety-critical systems (such as ADAS brake control) are too significant to ignore regardless of difficulty. Conversely, negligible impact always produces verdict 1 because low-harm scenarios do not warrant resource-intensive treatment, even if the attack is trivially easy.
See Also
