1717
Strategy = Attack Surface Reduction
Store state information and sensitive data on the server side only. Ensure that the system
definitively and unambiguously keeps track of its own state and user state and has rules defined
for legitimate state transitions. Do not allow any application user to affect state directly in any
way other than through legitimate actions leading to state transitions. If information must be
stored on the client, do not do so without encryption and integrity checking, or otherwise having
a mechanism on the server side to catch tampering. Use a message authentication code (MAC)
algorithm, such as Hash Message Authentication Code (HMAC) [REF-529]. Apply this against
the state or sensitive data that has to be exposed, which can guarantee the integrity of the data -
i.e., that the data has not been modified. Ensure that a strong hash function is used (CWE-328).
Phase: Architecture and Design
Strategy = Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides
constructs that make this weakness easier to avoid. With a stateless protocol such as HTTP, use
a framework that maintains the state for you. Examples include ASP.NET View State [REF-756]
and the OWASP ESAPI Session Management feature [REF-45]. Be careful of language features
that provide state support, since these might be provided as a convenience to the programmer
and may not be considering security.
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, in order to avoid CWE-602. 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.
Phase: Operation
Phase: Implementation
Strategy = Environment Hardening
When using PHP, configure the application so that it does not use register_globals. During
implementation, develop the application so that it does not rely on this feature, but be wary of
implementing a register_globals emulation that is subject to weaknesses such as CWE-95,
CWE-621, and similar issues.
Phase: Architecture and Design
Phase: Implementation
Strategy = Attack Surface Reduction
Understand all the potential areas where untrusted inputs can enter your software: parameters
or arguments, cookies, anything read from the network, environment variables, reverse DNS
lookups, query results, request headers, URL components, e-mail, files, filenames, databases,
and any external systems that provide data to the application. Remember that such inputs may
be obtained indirectly through API calls. Identify all inputs that are used for security decisions and
determine if you can modify the design so that you do not have to rely on submitted inputs at all.
For example, you may be able to keep critical information about the user's session on the server
side instead of recording it within external data.
Demonstrative Examples
Example 1:
The following code excerpt reads a value from a browser cookie to determine the role of the user.
Example Language: Java (Bad)
Cookie[] cookies = request.getCookies();
CWE Version 4.14
CWE-807: Reliance on Untrusted Inputs in a Security Decision
CWE-807: Reliance on Untrusted Inputs in a Security Decision