Client-Side Enforcement of Server-Side Security

Description

The product is composed of a server that relies on the client to implement a mechanism that is intended to protect the server.

Extended Description

When the server relies on protection mechanisms placed on the client side, an attacker can modify the client-side behavior to bypass the protection mechanisms, resulting in potentially unexpected interactions between the client and server. The consequences will vary, depending on what the mechanisms are trying to protect.

Common Consequences 2

Scope: Access ControlAvailability

Impact: Bypass Protection MechanismDoS: Crash, Exit, or Restart

Client-side validation checks can be easily bypassed, allowing malformed or unexpected input to pass into the application, potentially as trusted data. This may lead to unexpected states, behaviors and possibly a resulting crash.

Scope: Access Control

Impact: Bypass Protection MechanismGain Privileges or Assume Identity

Client-side checks for authentication can be easily bypassed, allowing clients to escalate their access levels and perform unintended actions.

Potential Mitigations 4

Phase: Architecture and Design

For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server. Even though client-side checks provide minimal benefits with respect to server-side security, they are still useful. First, they can support intrusion detection. If the server receives input that should have been rejected by the client, then it may be an indication of an attack. Second, client-side error-checking can provide helpful feedback to the user about the expectations for valid input. Third, there may be a reduction in server-side processing time for accidental input errors, although this is typically a small savings.

Phase: Architecture and Design

If some degree of trust is required between the two entities, then use integrity checking and strong authentication to ensure that the inputs are coming from a trusted source. Design the product so that this trust is managed in a centralized fashion, especially if there are complex or numerous communication channels, in order to reduce the risks that the implementer will mistakenly omit a check in a single code path.

Phase: Testing

Use dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

Phase: Testing

Use tools and techniques that require manual (human) analysis, such as penetration testing, threat modeling, and interactive tools that allow the tester to record and modify an active session. These may be more effective than strictly automated techniques. This is especially the case with weaknesses that are related to design and business rules.

Demonstrative Examples 2

This example contains client-side code that checks if the user authenticated successfully before sending a command. The server-side code performs the authentication in one step, and executes the command in a separate step.

CLIENT-SIDE (client.pl)

Code Example:Good
Perl
perlusername/pass is valid, go ahead and update the info!*perl

SERVER-SIDE (server.pl):

Code Example:Bad
Perl
perldoes not close the socket on failure; assumes the*perl

The server accepts 2 commands, "AUTH" which authenticates the user, and "CHANGE-ADDRESS" which updates the address field for the username. The client performs the authentication and only sends a CHANGE-ADDRESS for that user if the authentication succeeds. Because the client has already performed the authentication, the server assumes that the username in the CHANGE-ADDRESS is the same as the authenticated user. An attacker could modify the client by removing the code that sends the "AUTH" command and simply executing the CHANGE-ADDRESS.

ID : DX-153

In 2022, the OT:ICEFALL study examined products by 10 different Operational Technology (OT) vendors. The researchers reported 56 vulnerabilities and said that the products were "insecure by design" [REF-1283]. If exploited, these vulnerabilities often allowed adversaries to change how the products operated, ranging from denial of service to changing the code that the products executed. Since these products were often used in industries such as power, electrical, water, and others, there could even be safety implications.

Multiple vendors used client-side authentication in their OT products.

Observed Examples 5

CVE-2022-33139SCADA system only uses client-side authentication, allowing adversaries to impersonate other users.

CVE-2006-6994ASP program allows upload of .asp files by bypassing client-side checks.

CVE-2007-0163steganography products embed password information in the carrier file, which can be extracted from a modified client.

CVE-2007-0164steganography products embed password information in the carrier file, which can be extracted from a modified client.

CVE-2007-0100client allows server to modify client's configuration and overwrite arbitrary files.

References 2

Writing Secure Code

Michael Howard and David LeBlanc

Microsoft Press

04-12-2002

https://www.microsoftpressstore.com/store/writing-secure-code-9780735617223

ID: REF-7

OT:ICEFALL: The legacy of "insecure by design" and its implications for certifications and risk management

Forescout Vedere Labs

20-06-2022

https://www.forescout.com/resources/ot-icefall-report/

ID: REF-1283