Each guideline in the CERT C Coding Standard contains a risk assessment section that attempts to provide software developers with an indication of the potential consequences of not addressing a particular rule or recommendation in their code (along with some indication of expected remediation costs). This information may be used to prioritize the repair of rule violations by a development team. The metric is designed primarily for remediation projects. It is generally assumed that new code will be developed to be compliant with the entire coding standard and applicable recommendations.
Priority and Levels
Each rule and recommendation has an assigned priority. Priorities are assigned using a metric based on Failure Mode, Effects, and Criticality Analysis (FMECA) [IEC 60812]. Three values are assigned for each rule on a scale of 1 to 3 for severity, likelihood, and remediation cost.
Severity—How serious are the consequences of the rule being ignored?
Value
Meaning
Examples of Vulnerability
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 can lead to an exploitable vulnerability?
Value
Meaning
1
Unlikely
2
Probable
3
Likely
Remediation Cost—How expensive is it to comply with the rule?
Value
Meaning
Detection
Correction
1
High
Manual
Manual
2
Medium
Automatic
Manual
3
Low
Automatic
Automatic
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. The products range from 1 to 27, although only the following 10 distinct values are possible: 1, 2, 3, 4, 6, 8, 9, 12, 18, and 27. Rules and recommendations with a priority in the range of 1 to 4 are Level 3 rules, 6 to 9 are Level 2, and 12 to 27 are Level 1. The following are possible interpretations of the priorities and levels.
Priorities and Levels
Level
Priorities
Possible Interpretation
L1
12, 18, 27
High severity, likely, inexpensive to repair
L2
6, 8, 9
Medium severity, probable, medium cost to repair
L3
1, 2, 3, 4
Low severity, unlikely, expensive to repair
Specific projects may begin remediation by implementing all rules at a particular level before proceeding to the lower priority rules, as shown in the following illustration:
Recommendations are not compulsory and are provided for information purposes only.
Automated Detection
Both rules and recommendations frequently have sections that describe automated detection. These sections provide additional information on analyzers that can automatically diagnose violations of coding guidelines. Most automated analyses for the C programming language are neither sound nor complete, so the inclusion of a tool in this section typically means that the tool can diagnose some violations of this particular rule. Although the Secure Coding Validation Suite can be used to test the ability of analyzers to diagnose violations of rules from ISO/IEC TS 19761, no currently available conformance test suite can assess the ability of analyzers to diagnose violations of the rules in this wiki. Consequently, the information in automated detection sections may be
- Provided by the vendors
- Determined by CERT by informally evaluating the analyzer
- Determined by CERT by reviewing the vendor documentation
Where possible, we try to reference the exact version of the tool for which the results were obtained. Because these tools evolve continuously, this information can rapidly become dated and obsolete.
Related Vulnerabilities
The risk analysis sections also contain a link to search for related vulnerabilities on the CERT website. Whenever possible, CERT Vulnerability Notes are tagged with a keyword corresponding to the unique ID of the coding guideline. This search provides you with an up-to-date list of real-world vulnerabilities that have been determined to be at least partially caused by a violation of this specific guideline. These vulnerabilities are labeled as such only when the vulnerability analysis team at the CERT/CC is able to evaluate the source code and precisely determine the cause of the vulnerability. Because many vulnerability notes refer to vulnerabilities in closed-source software systems, it is not always possible to provide this additional analysis. Consequently, the related vulnerabilities field tends to be somewhat sparsely populated.
Related Guidelines
The related guidelines sections contain links to guidelines in related standards, technical specifications, and guideline collections such as Information Technology—Programming Languages, Their Environments and System Software Interfaces—C Secure Coding Rules [ISO/IEC TS 17961:2013]; Information Technology—Programming Languages—Guidance to Avoiding Vulnerabilities in Programming Languages through Language Selection and Use [ISO/IEC TR 24772:2013]; MISRA C 2012: Guidelines for the Use of the C Language in Critical Systems [MISRA C:2012]; and CWE IDs in MITRE’s Common Weakness Enumeration (CWE) [MITRE 2013].
You can create a unique URL to get more information on CWEs by appending the relevant ID to the end of a fixed string. For example, to find more information about CWE-192, Integer Coercion Error,” you can append 192.html to http://cwe.mitre.org/data/definitions/ and enter the resulting URL in your browser: http://cwe.mitre.org/data/definitions/192.html.
The other referenced technical specifications, technical reports, and guidelines are commercially available.
Bibliography
Most guidelines have a small bibliography section that lists documents and section in those documents that provide information relevant to the rule or recommendation.
