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Capec-1 Detail

Accessing Functionality Not Properly Constrained by ACLs

Standard Software Hardware Likelihood: High Typical Severity: High

Parents: 122

Children: 58 679 680 681

Threats: T72 T263 T271 T277 T280 T286 T293 T307 T336 T340 T383 T386 T390 T396 T399 T405

Description

In applications, particularly web applications, access to functionality is mitigated by an authorization framework. This framework maps Access Control Lists (ACLs) to elements of the application's functionality; particularly URL's for web apps. In the case that the administrator failed to specify an ACL for a particular element, an attacker may be able to access it with impunity. An attacker with the ability to access functionality not properly constrained by ACLs can obtain sensitive information and possibly compromise the entire application. Such an attacker can access resources that must be available only to users at a higher privilege level, can access management sections of the application, or can run queries for data that they otherwise not supposed to.

Not present

Explore

  1. Survey: The attacker surveys the target application, possibly as a valid and authenticated user

    2. Techniques
    Spidering web sites for all available links
    Brute force guessing of resource names
    Brute force guessing of user names / credentials
    Brute force guessing of function names / actions

  2. Identify Functionality: At each step, the attacker notes the resource or functionality access mechanism invoked upon performing specific actions

    3. Techniques
    Use the web inventory of all forms and inputs and apply attack data to those inputs.
    Use a packet sniffer to capture and record network traffic
    Execute the software in a debugger and record API calls into the operating system or important libraries. This might occur in an environment other than a production environment, in order to find weaknesses that can be exploited in a production environment.
Experiment

  1. Iterate over access capabilities: Possibly as a valid user, the attacker then tries to access each of the noted access mechanisms directly in order to perform functions not constrained by the ACLs.

    2. Techniques
    Fuzzing of API parameters (URL parameters, OS API parameters, protocol parameters)
  1. The application must be navigable in a manner that associates elements (subsections) of the application with ACLs.
  2. The various resources, or individual URLs, must be somehow discoverable by the attacker
  3. The administrator must have forgotten to associate an ACL or has associated an inappropriately permissive ACL with a particular navigable resource.
  1. None: No specialized resources are required to execute this type of attack.
Low
In order to discover unrestricted resources, the attacker does not need special tools or skills. They only have to observe the resources or access mechanisms invoked as each action is performed and then try and access those access mechanisms directly.
Authorization Access Control Confidentiality
Gain Privileges Gain Privileges Gain Privileges
  1. Implementing the Model-View-Controller (MVC) within Java EE's Servlet paradigm using a "Single front controller" pattern that demands that brokered HTTP requests be authenticated before hand-offs to other Action Servlets. If no security-constraint is placed on those Action Servlets, such that positively no one can access them, the front controller can be subverted.

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