An adversary adds duplicate HTTP GET/POST parameters by injecting query string delimiters. Via HPP it may be possible to override existing hardcoded HTTP parameters, modify the application behaviors, access and, potentially exploit, uncontrollable variables, and bypass input validation checkpoints and WAF rules.
Typical Severity
Medium
Relationships
This table shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf and ParentOf, and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.
Nature
Type
ID
Name
ChildOf
Standard Attack Pattern - A standard level attack pattern in CAPEC is focused on a specific methodology or technique used in an attack. It is often seen as a singular piece of a fully executed attack. A standard attack pattern is meant to provide sufficient details to understand the specific technique and how it attempts to accomplish a desired goal. A standard level attack pattern is a specific type of a more abstract meta level attack pattern.
Standard Attack Pattern - A standard level attack pattern in CAPEC is focused on a specific methodology or technique used in an attack. It is often seen as a singular piece of a fully executed attack. A standard attack pattern is meant to provide sufficient details to understand the specific technique and how it attempts to accomplish a desired goal. A standard level attack pattern is a specific type of a more abstract meta level attack pattern.
Find User Input: The adversary finds anywhere in the web application that uses user-supplied input in a form or action. This can also be found by looking at parameters in the URL in the navigation bar of the browser
Experiment
Add Duplicate Parameter Values: Once the adversary has identified what user input is used as HTTP parameters, they will add duplicates to each parameter one by one to observe the results. If the response from the HTTP request shows the duplicate parameter value concatenated with the original parameter value in some way, or simply just the duplicate parameter value, then HPP is possible.
Techniques
In the URL, add a duplicate parameter by using the "&" delimiter. For example "par1=val1" becomes "par1=val1&par1=val2". Depending on the backend API, this could be treated as "par1=val1, val2", which could lead to par1 being set to val2, ignoring val1.
If the request is created based on user input directly on the page, the adversary will test by adding an encoded delimiter to the input. For example, the adverary might supply "1000%26action=withdraw" and the backend might interpret a POST request with the paramters "action=deposit&amount=1000&action=withdraw"
Exploit
Leverage HPP: Once the adversary has identified how the backend handles duplicate parameters, they will leverage this by polluting the paramters in a way that benefits them. In some cases, hardcoded parameters will be disregarded by the backend. In others, the adversary can bypass a WAF that might only check a parameter before it has been concatenated by the backend, resulting in malicious queries getting through.
Prerequisites
HTTP protocol is used with some GET/POST parameters passed
Resources Required
Any tool that enables intercepting and tampering with HTTP requests
Mitigations
Configuration: If using a Web Application Firewall (WAF), filters should be carefully configured to detect abnormal HTTP requests
Design: Perform URL encoding
Implementation: Use strict regular expressions in URL rewriting
Implementation: Beware of multiple occurrences of a parameter in a Query String
Related Weaknesses
A Related Weakness relationship associates a weakness with this attack pattern. Each association implies a weakness that must exist for a given attack to be successful. If multiple weaknesses are associated with the attack pattern, then any of the weaknesses (but not necessarily all) may be present for the attack to be successful. Each related weakness is identified by a CWE identifier.
Description
This table shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf and ParentOf, and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.
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