CWE-602: 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.

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.

Abstraction: ClassAn abstract weakness, independent of any specific language or technology.
Likelihood of exploit: Medium
Status: Draft

Common consequences

Access ControlAvailability
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.

Potential mitigations

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...
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.

Related weaknesses

Parent weaknesses

CWE-693Protection Mechanism Failure

Child weaknesses

Can lead to

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

Peers

CAPEC attack patterns that exploit it

Description

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

Common consequences

Access ControlAvailability

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.

Potential mitigations

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...

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.