Positive security model

This is a principle or a set of principles. To view all principles, please see the Principle Category page.

Description

A "positive" security model (also known as "whitelist") is one that defines what is allowed, and rejects everything else. This should be contrasted with a "negative" (or "blacklist") security model, which defines what is disallowed, while implicitly allowing everything else.

The positive security model can be applied to a number of different application security areas. For example, when performing input validation, the positive model dictates that you should specify the characteristics of input that will be allowed, as opposed to trying to filter out bad input. In the access control area, the positive model is to deny access to everything, and only allow access to specific authorized resources or functions. If you've ever had to deal with a network firewall, then you've probably encountered this application of the positive model.

The benefit of using a positive model is that new attacks, not anticipated by the developer, will be prevented. However, the negative model can be quite tempting when you're trying to prevent an attack on your site. Ultimately, however, adopting the negative model means that you'll never be quite sure that you've addressed everything. You'll also end up with a long list of negative signatures to block that has to be maintained.

Examples

isAuthorized

if(ESAPI.accessController().isAuthorizedForFunction(ADMIN_FUNCTION)) {
  doAdminFunction();
}
else {
  doNormalFunction();
}

In this example, a validation happens that verifies if the active user is allowed to execute ADMIN_FUNCTIONS. If this is the case, the requested admin method doAdminFunction() will be executed, otherwise the default and non-administrative privileges requiring method doNormalFunction() is executed.

Related Vulnerabilities

• Improper error handling

Related Controls

• Authorization
• Error handling
• Web Application Firewall

References

• Category:OWASP Enterprise Security API