Adding Coding Rules

Messages

Issue messages should contain the remediation message for bug and quality rules. For potential-bug rules, it should make it explicit that a manual review is required. It should be in the imperative mood ("Do x"), and therefore start with a verb.

An issue message should always end with a period ('.') since it is an actual sentence, unless it ends with a regular expression, in which case the regular expression should be preceded by a colon and should end the message.

Any piece of code in the the rule message should be double-quoted (and not single-quoted). Moreover, if an issue is triggered because a number was above a threshold value, then both the number and the threshold value should be mentioned in the issue message.

Sample messages:

• Remove or refactor this useless "switch" statement. // Compliant
• This "switch" statement is useless and should be refactored or removed. // Noncompliant
• Every "switch" statement shall have at least one case-clause. // Noncompliant
• Rename this variable to comply with the regular expression: [a-z]+ // Compliant

With the default regular expression [a-z][a-zA-Z0-9]+:

try { /* ... */ } catch (Exception e) { LOGGER.info("context"); } // Noncompliant; exception is lost
try { /* ... */ } catch (Exception e) { LOGGER.info(e); } // Noncompliant; context is required
try { /* ... */ } catch (Exception e) { LOGGER.info(e.getMessage()); } // Noncompliant; exception is lost (only message is preserved)
try {
/* ... */
} catch (Exception e) { // Noncompliant - exception is lost
throw new RuntimeException("context");
}

try { /* ... */ } catch (Exception e) { LOGGER.info("context", e); }
try {
/* ... */
} catch (Exception e) {
throw new RuntimeException("context", e);
}

@Override
public void myMethod() throws Exception {...}

Guidelines for Hotspot rules

See RSPEC-4721 for an example of Hotspot rule.

Titles

• The title should start with a verb in the present participle form (-ing)
• The title should end with "is security-sensitive"

Noncompliant Title Examples:

• Avoid executing OS commands

Compliant Solution:

• Executing OS commands is security-sensitive
• Deserializing objects from an untrusted source is security-sensitive

Descriptions

Rule descriptions should contain the following sections in the listed order:

• Rationale (unlabeled) - explaining why this rule make sense.

  • It starts with a copy of the title. The "is security sensitive" part can be replaced with "can lead to ..." when there is one risk and it is easy to describe in a short manner.
  • Next is added the phrase "For example, it has led in the past to the following vulnerabilities:".
  • Next is a list of CVE links formatted as bullet points. Each CVE should point to their description on the (Example: CVE-2018-12465).

• Ask Yourself Whether - listing a set of questions which the developer should ask herself/himself.

  • Those questions should check if the context in which the code is makes it dangerous. For example, if some code enables a user to insert custom data the database, one of the questions could be: Is the user input sanitized?
  • Some additional questions can be added to remind the developer that there might not be a need for this code. For example, if some code enables a user to send and then execute custom code, the question could be: Does the user really need to execute code dynamically?
  • This section ends with "You are at risk if you answered yes to any of those questions." with an asterisk marking the corresponding questions if it is not the case for all of them.

• Recommended Secure Coding Practices - describing all the ways to mitigate the risk.

  • It usually contains a mix of all the advices provided by OWASP rules.
  • Add detailed solutions whenever possible.

• one of the following:

  • Noncompliant Code Example - same as for Bug, Vulnerability and Code Smell rules. some code can be added to give an example of dangerous context. For example: putting a password in an insecure cookie.
  • Sensitive Code Example - use this instead of "Noncompilant code example" when the Hotspot highlights some code which is not dangerous but might be the source of some vulnerability. Example: an opening Socket.
• See (optional) - same as for Bug, Vulnerability and Code Smell rules.
• Deprecated (optional) - listing replacement rules with links.

Guidelines regarding COBOL, keywords and code are the same as for other rules.

Messages

Most of the time you can paraphrase the title:

• start the sentence with "Make sure that"
• replace "is security-sensitive" with "is safe here"

However for some rules it can make sense to change the title. See the examples below:

• Title: Executing OS commands is security-sensitive

  • Message: make sure that executing this OS command is safe here.

• Title: Delivering code in production with debug mode activated is security-sensitive

  • Message: Make sure this debug mode is deactivated before delivering the code in production.

Guidelines applicable to all rules

See/References

When a reference is made to a standards specification, e.g. MISRA, the following steps must also be taken:

• add any related tags, such as: security, bug, &etc.
• add the relevant standard-related tag/label such as cwe, misra, etc. (If you forget, the overnight automation will remember for you.)
• update the appropriate field on the References tab with the cited id. (If you forget, the overnight automation will remember for you.)

If needed, references to other rules should be listed under a "See also" heading. If a "See" heading exists in the rule, then the "See also" title should be at the h3 level. Otherwise, use an h2 for it.

Other rules should be linked to only if they are related or contradictory (such as a pair of rules about where { should go).

Why list references to other rules under "see also" instead of "see"? The see section is used to support the current rule, and one rule cannot be used as justification for another rule.

Rule Type

Now that you've fleshed out the description, you should have a fairly clear idea of what type of rule this is, but to be explicit:

Bug - Something that's wrong or potentially wrong.

Code Smell - Something that will confuse a maintainer or cause her to stumble in her reading of the code.

Vulnerability - Something that has a high chance of being exploited by an attacker.

HotSpot - Something that could result in a vulnerability depending on the context in which this code is present.

Sometimes the line between Bug and Code Smell is fuzzy. When in doubt, ask yourself: "Is code that breaks this rule doing what the programmer probably intended?" If the answer is "probably not" then it's a Bug. Everything else is a Code Smell.

Default severities

When assessing the default severity of a rule, the first thing to do is ask yourself "what's the worst thing that could happen?" In answering, you should factor in Murphy's Law without predicting Armageddon.

Once you have your answer, it's time to assess whether the Impact and Likelihood of the Worst Thing are High or Low. To do that, ask yourself these specific questions:

Vulnerability

• Impact: Could the exploitation of the vulnerability result in significant damage to your assets or your users? (Yes = High)
• Likelihood: What is the probability a hacker will be able to exploit the issue?

Bug

• Impact: Could the bug cause the application to crash or corrupt stored data? (Languages where an error can cause program termination: COBOL, Python, PL/SQL, RPG.)
• Likelihood: What is the probability the worst will happen?

Code Smell

• Impact: Could the Code Smell lead a maintainer to introduce a bug?
• Likelihood: What is the probability the worst will happen?

Once you have your Impact and Likelihood assessments, the rest is easy:

	impact	likelihood
Blocker
Critical
Major
Minor

Tags

Rules can have 0-n tags, although most rules should have at least one. Many of the common-across-languages tags are described in the issues docs.

Evaluation of the remediation cost

For most rules, the SQALE remediation cost is constant per issue. The goal of this section is to help defining the value of this constant and to unify the way those estimations are done to prevent having some big discrepancies among language plugins.

First step, classify the effort to do the remediation :

1. TRIVIAL No need to understand the logic and no potential impact. Examples: remove unused imports, replace tabulations by spaces, remove call to System.out.println() used for debugging purpose, ...
2. EASY No need to understand the logic but potential impacts. Examples: rename a method, rename a parameter, remove unused private method, ...
3. MEDIUM Understanding the logic of a piece of code is required before doing a little and easy refactoring (1 or 2 lines of code). But understanding the big picture is not required. Examples : CURSORs should not be declared inside a loop, EXAMINE statement should not be used, IF should be closed with END-IF, ...
4. MAJOR Understanding the logic of a piece of code is required and it's up to the developer to define the remediation action. Examples: Too many nested IF statements, Methods should not have too many parameters, UNION should not be used in SQL SELECT statements, Public java method should have a javadoc, Avoid using deprecated methods, ...
5. HIGH The remediation action might lead to locally impact the design of the application. Examples: Classes should not have too many responsibilities, Cobol programs should not have too many lines of code, Architectural constraint, ...
6. COMPLEX The remediation action might lead to impact the overall design of the application. Examples: Avoid cycles between packages, ...

Then use the following table to get the remediation cost according to the required remediation effort and to the language:

For rules using either the "linear" or "linear with offset" remediation functions, the "Effort To Fix" field must be fed on each issue and this field is used to compute the remediation cost.

Issue location(s) and highlighting

For any given rule, highlighting behavior should be consistent across languages within the bounds of what's relevant for each language.

When possible, each issue should be raised on the line of code that needs correction, with highlighting limited to the portion of the line to be corrected. For example:

• an issue for a misnamed method should be raised on the line with the method name, and the method name itself should be highlighted.

When correcting an issue requires action across multiple lines, the issue should be raised on the the lowest block that encloses all relevant lines. For example an issue for:

• method complexity should be raised on the method signature
• method count in a class should be raised on the class declaration

When an issue could be made clearer by highlighting multiple code segments, such as a method complexity issue, additional issue locations may be highlighted, and additional messages may optionally be logged for those locations. In general, these guidelines should be followed for secondary issue locations:

• highlight the minimum code to show the line's contribution to the issue.
• avoid using an additional message if the secondary location is likely to be on the same issue as the issue itself. For example: the rule "Parameters should be final" will raise an issue on the method name, and highlight each non-final parameter. Since all locations are likely to be on the same line, additional messages would only confuse the issue.
• don't write a novel. The message for a secondary location is meant to be a hint to push the user in the right direction. Don't take over the interface with a narrative.