Wednesday, 31 May 2023

Automating REST Security Part 1: Challenges

Although REST has been a dominant choice for API design for the last decade, there is still little dedicated security research on the subject of REST APIs. The popularity of REST contrasts with a surprisingly small number of systematic approaches to REST security analysis. This contrast is also reflected in the low availability of analysis tools and best security practices that services may use to check if their API is secure.

In this blog series, we try to find reasons for this situation and what we can do about it. In particular, we will investigate why general REST security assessments seem more complicated than other API architectures. We will likewise discuss how we may still find systematic approaches for REST API analysis despite REST's challenges. Furthermore, we will present REST-Attacker, a novel analysis tool designed for automated REST API security testing. In this context, we will examine some of the practical tests provided by REST-Attacker and explore the test results for a small selection of real-world API implementations.


Christoph Heine


 Understanding the Problem with REST

When evaluating network components and software security, we often rely on specifications for how things should work. For example, central authorities like the IETF standardize many popular web technologies such as HTTP, TLS or DNS. API architectures and designs can also be standardized. Examples of these technologies are SOAP and the more recent GraphQL language specification. Standardization of web standards usually influences their security. Drafting may involve a public review process before publication. This process can identify security flaws or allow the formulation of official implementation and usage best practices. Best practices are great for security research as a specification presents clear guidelines on how an implementation should behave and why.

The situation for REST is slightly different. First of all, REST is not a standard in the sense that there is no technical specification for its implementation. Instead, REST is an architecture style which is more comparable to a collection of paradigms (client-server architecture, statelessness, cacheability, uniform interface, layering, and code-on-demand). Notably, REST has no strict dependency on other web technologies. It only defines how developers should use components but not what components they should use. This paradigm makes REST very flexible as developers are not limited to any particular protocol, library, or data structure.

Furthermore, no central authority could define rules or implementation guidelines. Roy Fielding created the original definition of REST as a design template for the HTTP/1.1 standard in 2000. It is the closest document resembling a standard. However, the document merely explains the REST paradigms and does not focus on security implications.

The flexibility of the REST architecture is probably one of the primary reasons why security research can be challenging. If every implementation is potentially different, how are we supposed to create common best practices, let alone test them consistently across hundreds of APIs? Fortunately for us, not every API tries to reinvent the wheel entirely. In practice, there are a lot of similarities between implementations that may be used to our advantage.

Generalizing REST Security

The most glaring similarity between REST API implementations is that most, if not all, are based on HTTP. If you have worked with REST APIs before, this statement might sound like stating the obvious. However, remember that REST technically does not require a specific protocol. Assuming that every REST API uses HTTP, we can use it as a starting point for a generalization of REST API security. Knowing that we mainly deal with HTTP is also advantageous because HTTP - unlike REST - is standardized. Although HTTP is still complex, it gives us a general idea of what we can expect.

Another observation is that REST API implementations reuse several standardized components in HTTP for API communication. Control parameters and actions in an API request are mapped to components in a generic HTTP request. For example, a resource that an API request operates on, is specified via the HTTP URL. Actions or operations on the said resource are identified and mapped to HTTP methods defined by the HTTP standard, usually GET, POST, DELETE, PUT, and PATCH. API operations retain their intended action from HTTP, i.e., GET retrieves a resource, DELETE removes a resource, and so on. In REST API documentation, we can often find a description of available API endpoints using HTTP "language":

Since the URL and the HTTP method are sufficient to build a basic HTTP request, we can potentially create an API requests if we know a list of REST endpoints. In practice, the construction of such requests can be more complicated because the API may have additional parameter requirements for their requests, e.g., query, header, or body content. Another problem is finding valid IDs of resources can be difficult. Interestingly, we can infer each endpoint's action based on the HTTP method, even without any context-specific knowledge about the API.

We can also find components taken from the HTTP standard in the API response. The requested operation's success or failure is usually indicated using HTTP status codes. They retain their meaning when used in REST APIs. For example, a 200 status code indicates success, while a 401 status code signifies missing authorization (in the preceding API request). This behavior again can be inferred without knowing the exact purpose of the API.

Another factor that influences REST's complexity is its statelessness paradigm. Essentially, statelessness requires that the server does not keep a session between individual requests. As a result, every client request must be self-contained, so multi-message operations are out of the picture. It also effectively limits interaction with the API to two HTTP messages: client request and server response. Not only does this make API communication easier to comprehend, but it also makes testing more manageable since we don't have to worry as much about side effects or keeping track of an operations state.

Implementing access control mechanisms can be more complicated, but we can still find general similarities. While REST does not require any particular authentication or authorization methods, the variety of approaches found in practice is small. REST API implementations usually implement a selection of these methods:

  • HTTP Basic Authentication (user authentication)
  • API keys (client authentication)
  • OAuth2 (authorization)

Two of these methods, OAuth2 and HTTP Basic Authentication, are standardized, while API keys are relatively simple to handle. Therefore, we can generalize access control to some degree. However, access control can be one of the trickier parts of API communication as there may be a lot of API-specific configurations. For example, OAuth2 authorization allows the API to define multiple access levels that may be required to access different resources or operations. How access control data is delivered in the HTTP message may also depend on the API, e.g., by requiring encoding of credentials or passing them in a specified location of the HTTP message (e.g. header, query, or body).

Finding a Systematic Approach for REST API Analysis

So far, we've only discussed theoretical approaches scatching a generic REST API analysis. For implementing an automated analysis tool, we need to adopt the hints that we used for our theoretical API analyses to the tool. For example, the tool would need to know which API endpoints exist to create API requests on its own.

The OpenAPI specification is a popular REST API description format that can be used for such purpose. An OpenAPI file contains a machine-readable definition (as JSON or YAML) of an API's interface. Basic descriptions include the definition of the API endpoints, but can optionally contain much more content and other types of useful information. For example, an endpoint definition may include a list of required parameters for requests, possible response codes and content schemas of API responses. The OpenAPI can even describe security requirements that define what types of access control methods are used.

{     "openapi": "3.1.0",     "info": {         "title": "Example API",         "version": "1.0"     },     "servers": [         {             "url": ""         }     ],     "paths": {         "/user/info": {             "get": {                 "description": "Returns information about a user.",                 "parameters": [                     {                     "name": "id",                     "in": "query",                     "description": "User ID",                     "required": true                     }                 ],                 "responses": {                     "200": {                         "description": "User information.",                         "content": {                             "application/json": {                                 "schema": {                                     "type": "object",                                     "items": {                                         "$ref": "#/components/schemas/user_info"                                     }                                 }                             }                         }                     }                 }             }         }     },     "security": [         {             "api_key": []         }     ] } 

As you can see from the example above, OpenAPI files allow tools to both understand the API and use the available information to create valid API requests. Furthermore, the definition can give insight into the expected behavior of the API, e.g., by checking the response definitions. These properties make the OpenAPI format another standard on which we can rely. Essentially, a tool that can parse and understand OpenAPI can understand any generic API. With the help of OpenAPI, tools can create and execute tests for APIs automatically. Of course, the ability of tools to derive tests still depends on how much information an OpenAPI file provides. However, wherever possible, automation can potentially eliminate a lot of manual work in the testing process.


When we consider the similarities between REST APIs and OpenAPI descriptions, we can see that there is potential for analyzing REST security with tools. Our next blog post discusses how such an implementation would look like. We will discuss REST-Attacker, our tool for analyzing REST APIs.

Further Reading

The feasibility of tool-based REST analysis has also been discussed in scientific papers. If you want to know more about the topic, you can start here:

  • Atlidakis et al., Checking Security Properties of Cloud Service REST APIs (DOI Link)
  • Lo et al., On the Need for a General REST-Security Framework (DOI Link)
  • Nguyen et al., On the Security Expressiveness of REST-Based API Definition Languages (DOI Link)


The REST-Attacker project was developed as part of a master's thesis at the Chair of Network & Data Security of the Ruhr University Bochum. I would like to thank my supervisors Louis Jannett, Christian Mainka, Vladislav Mladenov, and Jörg Schwenk for their continued support during the development and review of the project.

More information
  1. Pentest Tools Subdomain
  2. Hacker Tools Apk
  3. Best Pentesting Tools 2018
  4. Hacking Tools Download
  5. Hack Tools Github
  6. Pentest Tools Windows
  7. Hacker Tools Windows
  8. Hacker Tools List
  9. Hacker Tools Linux
  10. Hacking Tools Windows 10
  11. Free Pentest Tools For Windows
  12. Hacker Tools 2019
  13. Github Hacking Tools
  14. Hacker Tools For Mac
  15. Hacker Tools Github
  16. Hacker Tools Github
  17. Pentest Tools Bluekeep
  18. Hacker Tools List
  19. Pentest Tools Download
  20. Pentest Automation Tools
  21. Tools For Hacker
  22. Pentest Tools Android
  23. Pentest Tools Github
  24. Pentest Tools List
  25. World No 1 Hacker Software
  26. Hacking Tools Mac
  27. Hacking App
  28. Hacking Tools 2020
  29. Pentest Tools Apk
  30. Wifi Hacker Tools For Windows
  31. Hackers Toolbox
  32. Hack Tools For Mac
  33. Hack Tools 2019
  34. Underground Hacker Sites
  35. Hacking Tools For Windows 7
  36. Pentest Tools Download
  37. Hacker Tools For Ios
  38. Pentest Tools For Windows
  39. Pentest Tools Website Vulnerability
  40. Github Hacking Tools
  41. Hack Rom Tools
  42. Hack Tool Apk
  43. Hacking Tools 2019
  44. Pentest Tools List
  45. Hacker Tools List
  46. Pentest Tools For Android
  47. Hacker Tools
  48. Pentest Tools For Android
  49. Hacker Tools Apk Download
  50. Pentest Reporting Tools
  51. Hacker Tools Software
  52. Pentest Tools Framework
  53. Tools For Hacker
  54. Hacker Techniques Tools And Incident Handling
  55. Hack Tools Download
  56. How To Hack
  57. How To Install Pentest Tools In Ubuntu
  58. Hacking Tools For Windows 7
  59. Hacking Tools Github
  60. Pentest Tools List
  61. Hacking Tools Usb
  62. Hack Tools For Games
  63. Top Pentest Tools
  64. Hacker Tools Windows
  65. Hackrf Tools
  66. Hacking Tools 2020
  67. Top Pentest Tools
  68. Pentest Automation Tools
  69. Hack Tools Download
  70. Hack Tools For Games
  71. Black Hat Hacker Tools
  72. Hacker Tools For Ios
  73. Install Pentest Tools Ubuntu
  74. Hack And Tools
  75. Hacking Tools Hardware
  76. Pentest Tools Linux
  77. Tools 4 Hack
  78. Hacking Tools For Beginners
  79. Hack Tools Pc
  80. Pentest Tools For Windows
  81. Pentest Tools Find Subdomains
  82. Hacker Tools
  83. Pentest Tools Alternative
  84. Github Hacking Tools
  85. Pentest Tools Find Subdomains
  86. Hacker Tools Online
  87. What Is Hacking Tools
  88. Pentest Tools
  89. Hacking Tools For Games
  90. Hacking Tools
  91. Hacker Tools Free Download
  92. Hack Tools For Ubuntu
  93. Best Pentesting Tools 2018
  94. Hacking Tools For Windows
  95. Hacker Tools Apk Download
  96. Pentest Tools Windows
  97. Pentest Reporting Tools
  98. Hack Tools
  99. Hack Tools
  100. Hack Tool Apk
  101. Hack Tool Apk
  102. Pentest Tools For Ubuntu
  103. Hacking Tools For Windows
  104. Hacker Tools Free
  105. Nsa Hack Tools Download
  106. Hack Tools
  107. Hacker Tools Mac
  108. Pentest Tools For Windows
  109. Blackhat Hacker Tools
  110. Hacking Tools For Windows
  111. Hacker Security Tools
  112. Nsa Hack Tools
  113. Hack Tools Download
  114. Pentest Reporting Tools
  115. Hacker Tools For Ios
  116. Install Pentest Tools Ubuntu
  117. Hacker Tools For Windows
  118. Hacker Tools Free
  119. Hacking Tools For Games
  120. Hacker Tools 2020
  121. World No 1 Hacker Software
  122. Hacking Tools 2020
  123. Hacker Tools Free
  124. Hacking Tools Name