Common Attack Pattern Enumeration and Classification
A Community Resource for Identifying and Understanding Attacks
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.
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.
Skill or Knowledge Level: Low
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.
In the case of web applications, use of a spider or other crawling software can allow an attacker to search for accessible pages not beholden to a security constraint.
More generally, noting the target resource accessed upon performing specific actions drives an understanding of the resources accessible from the current context.
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.
All resources must be constrained to be inaccessible by default followed by selectively allowing access to resources as dictated by application and business logic
In addition to a central controller, every resource must also restrict, wherever possible, incoming accesses as dictated by the relevant ACL.
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