Client-Side Enforcement of Server-Side Security

Opis

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

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.

Skutki

• Access Control, Availability

  Bypass Protection Mechanism; DoS: 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.

• Access Control

  Bypass Protection Mechanism; Gain Privileges or Assume Identity

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

Zapobieganie

• 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.

• 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.

Przykłady podatności

• CVE-2024-50653 Chain: e-commerce product has a "front-end restriction" for coupon use (CWE-602), but the server does not restrict the number of requests for the same coupon (CWE-799)
• CVE-2022-33139 SCADA system only uses client-side authentication, allowing adversaries to impersonate other users.
• CVE-2006-6994 ASP program allows upload of .asp files by bypassing client-side checks.
• CVE-2007-0163 steganography products embed password information in the carrier file, which can be extracted from a modified client.
• CVE-2007-0164 steganography products embed password information in the carrier file, which can be extracted from a modified client.
• CVE-2007-0100 client allows server to modify client's configuration and overwrite arbitrary files.

Słabość nadrzędna

• CWE-693 Protection Mechanism Failure

Może prowadzić do

• CWE-471 Modification of Assumed-Immutable Data (MAID)

Pokrewna

• CWE-290 Authentication Bypass by Spoofing
• CWE-300 Channel Accessible by Non-Endpoint

Słabości podrzędne

• CWE-565 Reliance on Cookies without Validation and Integrity Checking
• CWE-603 Use of Client-Side Authentication

Kiedy powstaje

• Architecture and Design — COMMISSION: This weakness refers to an incorrect design related to an architectural security tactic.
• Architecture and Design — Consider a product that consists of two or more processes or nodes that must interact closely, such as a client/server model. If the product uses protection schemes in the client in order to defend from attacks against the server, and the server does not use the same schemes, then an attacker could modify the client in a way that bypasses those schemes. This is a fundamental design flaw that is primary to many weaknesses.

Dotyczy

Not Language-Specific, ICS/OT, Mobile

Źródła

1. Writing Secure Code — Michael Howard, David LeBlanc, Chapter 23, "Client-Side Security Is an Oxymoron" Page 687, Microsoft Press, 2002
2. OT:ICEFALL: The legacy of "insecure by design" and its implications for certifications and risk management — Forescout Vedere Labs, 2022