Test Defenses Against Application Misuse (WSTG-BUSL-07)
WSTG-BUSL-07
Summary
The misuse and invalid use of valid functionality can identify attacks attempting to enumerate the web application, identify weaknesses, and exploit vulnerabilities. Tests should be undertaken to determine whether there are application-layer defensive mechanisms in place to protect the application.
The lack of active defenses allows an attacker to hunt for vulnerabilities without any recourse. The application's owner will thus not know their application is under attack.
Example
An authenticated user undertakes the following (unlikely) sequence of actions:
Attempt to access a file ID their roles is not permitted to download
Substitutes a single tick
'instead of the file ID numberAlters a GET request to a POST
Adds an extra parameter
Duplicates a parameter name/value pair
The application is monitoring for misuse and responds after the 5th event with extremely high confidence the user is an attacker. For example the application:
Disables critical functionality
Enables additional authentication steps to the remaining functionality
Adds time-delays into every request-response cycle
Begins to record additional data about the user's interactions (e.g. sanitized HTTP request headers, bodies and response bodies)
If the application does not respond in any way and the attacker can continue to abuse functionality and submit clearly malicious content at the application, the application has failed this test case. In practice the discrete example actions in the example above are unlikely to occur like that. It is much more probable that a fuzzing tool is used to identify weaknesses in each parameter in turn. This is what a security tester will have undertaken too.
Test Objectives
Generate notes from all tests conducted against the system.
Review which tests had a different functionality based on aggressive input.
Understand the defenses in place and verify if they are enough to protect the system against bypassing techniques.
How to Test
This test is unusual in that the result can be drawn from all the other tests performed against the web application. While performing all the other tests, take note of measures that might indicate the application has in-built self-defense:
Changed responses
Blocked requests
Actions that log a user out or lock their account
These may only be localized. Common localized (per function) defenses are:
Rejecting input containing certain characters
Locking out an account temporarily after a number of authentication failures
Localized security controls are not sufficient. There are often no defenses against general mis-use such as:
Forced browsing
Bypassing presentation layer input validation
Multiple access control errors
Additional, duplicated or missing parameter names
Multiple input validation or business logic verification failures with values that cannot be the result user mistakes or typos
Structured data (e.g. JSON, XML) of an invalid format is received
Blatant cross-site scripting or SQL injection payloads are received
Utilizing the application faster than would be possible without automation tools
Change in continental geo-location of a user
Change of user agent
Accessing a multi-stage business process in the wrong order
Large number of, or high rate of use of, application-specific functionality (e.g. voucher code submission, failed credit card payments, file uploads, file downloads, log outs, etc).
These defenses work best in authenticated parts of the application, although rate of creation of new accounts or accessing content (e.g. to scrape information) can be of use in public areas.
Not all the above need to be monitored by the application, but there is a problem if none of them are. By testing the web application, doing the above type of actions, was any response taken against the tester? If not, the tester should report that the application appears to have no application-wide active defenses against misuse. Note it is sometimes possible that all responses to attack detection are silent to the user (e.g. logging changes, increased monitoring, alerts to administrators and and request proxying), so confidence in this finding cannot be guaranteed. In practice, very few applications (or related infrastructure such as a web application firewall) are detecting these types of misuse.
Related Test Cases
All other test cases are relevant.
Remediation
Applications should implement active defenses to fend off attackers and abusers.
References
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