CAPEC-1: Accessing Functionality Not Properly Constrained by ACLs
Attack Pattern ID: 1
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.
Likelihood Of Attack
The table below 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.
Meta Attack Pattern - A meta level attack pattern in CAPEC is a decidedly abstract characterization of a specific methodology or technique used in an attack. A meta attack pattern is often void of a specific technology or implementation and is meant to provide an understanding of a high level approach. A meta level attack pattern is a generalization of related group of standard level attack patterns. Meta level attack patterns are particularly useful for architecture and design level threat modeling exercises.
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.
Detailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal.
Survey: The attacker surveys the target application, possibly as a valid and authenticated user
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
Identify Functionality: At each step, the attacker notes the resource or functionality access mechanism invoked upon performing specific actions
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.
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.
Fuzzing of API parameters (URL parameters, OS API parameters, protocol parameters)
The application must be navigable in a manner that associates elements (subsections) of the application with ACLs.
The various resources, or individual URLs, must be somehow discoverable by the attacker
The administrator must have forgotten to associate an ACL or has associated an inappropriately permissive ACL with a particular navigable resource.
In order to discover unrestricted resources, the attacker does not need special tools or skills. He only has to observe the resources or access mechanisms invoked as each action is performed and then try and access those access mechanisms directly.
None: No specialized resources are required to execute this type of attack.
The table below specifies different individual consequences associated with the attack pattern. The Scope identifies the security property that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in their attack. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a pattern will be used to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
In a J2EE setting, administrators can associate a role that is impossible for the authenticator to grant users, such as "NoAccess", with all Servlets to which access is guarded by a limited number of servlets visible to, and accessible by, the user.
Having done so, any direct access to those protected Servlets will be prohibited by the web container.
In a more general setting, the administrator must mark every resource besides the ones supposed to be exposed to the user as accessible by a role impossible for the user to assume. The default security setting must be to deny access and then grant access only to those resources intended by business logic.
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.
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.