CWE-472: External Control of Assumed-Immutable Web Parameter

Description:
The web application does not sufficiently verify inputs that are assumed to be immutable but are actually externally controllable, such as hidden form fields.

Extended Description:
If a web product does not properly protect assumed-immutable values from modification in hidden form fields, parameters, cookies, or URLs, this can lead to modification of critical data. Web applications often mistakenly make the assumption that data passed to the client in hidden fields or cookies is not susceptible to tampering. Improper validation of data that are user-controllable can lead to the application processing incorrect, and often malicious, input. 
             For example, custom cookies commonly store session data or persistent data across sessions. This kind of session data is normally involved in security related decisions on the server side, such as user authentication and access control. Thus, the cookies might contain sensitive data such as user credentials and privileges. This is a dangerous practice, as it can often lead to improper reliance on the value of the client-provided cookie by the server side application.

Affected languages: Not Language-Specific
Affected technologies: Web Based, Web Server
Parent weaknesses: CWE-642, CWE-471

Consequences:
  - Integrity: Modify Application Data

Detection methods:
  - Automated Static Analysis: Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without havin

Mitigations:
  - [Implementation] Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. 
                   When pe
  - [Implementation] Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous i

Demonstrative examples:
In this example, a web application uses the value of a hidden form field (accountID) without having done any input validation because it was assumed to be immutable.

String accountID = request.getParameter("accountID"); User user = getUserFromID(Long.parseLong(accountID));

Hidden fields should not be trusted as secure parameters.
An attacker can intercept and alter hidden fields in a post to the server as easily as user input fields. An attacker can simply parse the HTML for the substring:
<input type="hidden"

Real-world examples:
  - CVE-2002-0108: Forum product allows spoofed messages of other users via hidden form fields for name and e-mail address.
  - CVE-2000-0253: Shopping cart allows price modification via hidden form field.
  - CVE-2000-0254: Shopping cart allows price modification via hidden form field.
  - CVE-2000-0926: Shopping cart allows price modification via hidden form field.
  - CVE-2000-0101: Shopping cart allows price modification via hidden form field.