Each rule and recommendation in a secure coding standard has an assigned priority. Priorities are assigned using a metric based on Failure Mode, Effects, and Criticality Analysis (FMECA). Three values are assigned for each rule on a scale of 1 - 3 for:
- severity - how serious are the consequences of the rule being ignored;
1 = low (denial-of-service attack, abnormal termination)
2 = medium (data integrity violation, unintentional information disclosure)
3 = high (run arbitrary code)
- likelihood - how likely is it that a flaw, introduced by ignoring the rule, could lead to an exploitable vulnerability;
1 = unlikely
2 = probable
3 = likely
- remediation cost - how expensive is it to comply with the rule.
1 = high (manual detection and correction)
2 = medium (automatic detection / manual correction)
3 = low (automatic detection and correction)
The three values are then multiplied together for each rule. This product provides a measure that can be used in prioritizing the application of the rules. These products range from 1 to 27. Rules and recommendations with a priority in the range of 1-4 are level 3 rules, 6-9 are level 2, and 12-27 are level 1. As a result, it is possible to claim level 3, level 2, or complete compliance with a standard by implementing all rules in a level. Recommendations are not compulsory and are provided for information purposes only.