| Name |
Removing Important Client Functionality |
|
| Likelyhood of attack |
Typical severity |
| Medium |
High |
|
| Summary |
An attacker removes or disables functionality on the client that the server assumes to be present and trustworthy. Attackers can, in some cases, get around logic put in place to 'guard' sensitive functionality or data. Client applications may include functionality that a server relies on for correct and secure operation. This functionality can include, but is not limited to, filters to prevent the sending of dangerous content to the server, logical functionality such as price calculations, and authentication logic to ensure that only authorized users are utilizing the client. If an attacker can disable this functionality on the client, they can perform actions that the server believes are prohibited. This can result in client behavior that violates assumptions by the server leading to a variety of possible attacks. In the above examples, this could include the sending of dangerous content (such as scripts) to the server, incorrect price calculations, or unauthorized access to server resources. |
| Prerequisites |
The targeted server must assume the client performs important actions to protect the server or the server functionality. For example, the server may assume the client filters outbound traffic or that the client performs all price calculations correctly. Moreover, the server must fail to detect when these assumptions are violated by a client. |
| Execution Flow |
| Step |
Phase |
Description |
Techniques |
| 1 |
Explore |
[Probing] The attacker probes, through brute-forcing, reverse-engineering or other similar means, the functionality on the client that server assumes to be present and trustworthy. |
- The attacker probes by exploring an application's functionality and its underlying mapping to server-side components.
- The attacker reverse engineers client-side code to identify the functionality that the server relies on for the proper or secure operation.
|
| 2 |
Experiment |
[Determine which functionality to disable or remove] The attacker tries to determine which functionality to disable or remove through reverse-engineering from the list of functionality identified in the Explore phase. |
- The attacker reverse engineers the client-side code to determine which functionality to disable or remove.
|
| 3 |
Exploit |
[Disable or remove the critical functionality from the client code] Once the functionality has been determined, the attacker disables or removes the critical functionality from the client code to perform malicious actions that the server believes are prohibited. |
- The attacker disables or removes the functionality from the client-side code to perform malicious actions, such as sending of dangerous content (such as scripts) to the server.
|
|
| Solutions | Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side. Design: Ship client-side application with integrity checks (code signing) when possible. Design: Use obfuscation and other techniques to prevent reverse engineering the client code. |
| Related Weaknesses |
|
CWE ID
|
Description
|
| CWE-602 |
Client-Side Enforcement of Server-Side Security |
|
| Related CAPECS |
|
CAPEC ID
|
Description
|
| CAPEC-22 |
An attack of this type exploits vulnerabilities in client/server communication channel authentication and data integrity. It leverages the implicit trust a server places in the client, or more importantly, that which the server believes is the client. An attacker executes this type of attack by communicating directly with the server where the server believes it is communicating only with a valid client. There are numerous variations of this type of attack. |
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