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.

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.

Potential Impact

Integrity

Modify Application Data

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.

Bad

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:

Bad

<input type="hidden"

or even just "hidden". Hidden field values displayed later in the session, such as on the following page, can open a site up to cross-site scripting attacks.

Mitigations & Prevention

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 performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across relat

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 inputs after they have been checked.

Detection Methods

Automated Static Analysis High — 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 having to execute it. Typically, this is done by building a model of data flow and control flow, then sea

Real-World CVE Examples

CVE ID	Description
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.
CVE-2000-0102	Shopping cart allows price modification via hidden form field.
CVE-2000-0758	Allows admin access by modifying value of form field.
CVE-2002-1880	Read messages by modifying message ID parameter.
CVE-2000-1234	Send email to arbitrary users by modifying email parameter.
CVE-2005-1652	Authentication bypass by setting a parameter.
CVE-2005-1784	Product does not check authorization for configuration change admin script, leading to password theft via modified e-mail address field.
CVE-2005-2314	Logic error leads to password disclosure.
CVE-2005-1682	Modification of message number parameter allows attackers to read other people's messages.

Taxonomy Mappings

PLOVER: — Web Parameter Tampering
OWASP Top Ten 2007: A4 — Insecure Direct Object Reference
OWASP Top Ten 2004: A1 — Unvalidated Input

Frequently Asked Questions

What is CWE-472?

CWE-472 (External Control of Assumed-Immutable Web Parameter) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Base-level weakness. The web application does not sufficiently verify inputs that are assumed to be immutable but are actually externally controllable, such as hidden form fields.

How can CWE-472 be exploited?

Attackers can exploit CWE-472 (External Control of Assumed-Immutable Web Parameter) to modify application data. This weakness is typically introduced during the Implementation phase of software development.

How do I prevent CWE-472?

Key mitigations include: 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 stric

What is the severity of CWE-472?

CWE-472 is classified as a Base-level weakness (Medium abstraction). It has been observed in 13 real-world CVEs.