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.

Primary

Resultant

Assumed-Immutable Parameter Tampering

Implementation
OMISSION: This weakness is caused by missing a security tactic during the architecture and design phase.

Integrity
Modify Application Data
Without appropriate protection mechanisms, the client can easily tamper with cookies and similar web data. Reliance on the cookies without detailed validation can lead to problems such as SQL injection. If you use cookie values for security related decisions on the server side, manipulating the cookies might lead to violations of security policies such as authentication bypassing, user impersonation and privilege escalation. In addition, storing sensitive data in the cookie without appropriate protection can also lead to disclosure of sensitive user data, especially data stored in persistent cookies.

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 having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
High

Implementation
Input Validation

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 related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue."
Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

Implementation
Input Validation
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.

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"

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.

CVE-2002-0108
Forum product allows spoofed messages of other users via hidden form fields for name and e-mail address.
https://www.cve.org/CVERecord?id=CVE-2002-0108

CVE-2000-0253
Shopping cart allows price modification via hidden form field.
https://www.cve.org/CVERecord?id=CVE-2000-0253

CVE-2000-0254
Shopping cart allows price modification via hidden form field.
https://www.cve.org/CVERecord?id=CVE-2000-0254

CVE-2000-0926
Shopping cart allows price modification via hidden form field.
https://www.cve.org/CVERecord?id=CVE-2000-0926

CVE-2000-0101
Shopping cart allows price modification via hidden form field.
https://www.cve.org/CVERecord?id=CVE-2000-0101

CVE-2000-0102
Shopping cart allows price modification via hidden form field.
https://www.cve.org/CVERecord?id=CVE-2000-0102

CVE-2000-0758
Allows admin access by modifying value of form field.
https://www.cve.org/CVERecord?id=CVE-2000-0758

CVE-2002-1880
Read messages by modifying message ID parameter.
https://www.cve.org/CVERecord?id=CVE-2002-1880

CVE-2000-1234
Send email to arbitrary users by modifying email parameter.
https://www.cve.org/CVERecord?id=CVE-2000-1234

CVE-2005-1652
Authentication bypass by setting a parameter.
https://www.cve.org/CVERecord?id=CVE-2005-1652

CVE-2005-1784
Product does not check authorization for configuration change admin script, leading to password theft via modified e-mail address field.
https://www.cve.org/CVERecord?id=CVE-2005-1784

CVE-2005-2314
Logic error leads to password disclosure.
https://www.cve.org/CVERecord?id=CVE-2005-2314

CVE-2005-1682
Modification of message number parameter allows attackers to read other people's messages.
https://www.cve.org/CVERecord?id=CVE-2005-1682

Web Parameter Tampering

A4
Insecure Direct Object Reference
CWE More Specific

A1
Unvalidated Input
CWE More Specific

Allowed
This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

This is a primary weakness for many other weaknesses and functional consequences, including XSS, SQL injection, path disclosure, and file inclusion.
This is a technology-specific MAID problem.

PLOVER
2006-07-19
Draft 3
2006-07-19

Sean Eidemiller
Cigital
2008-07-01
added/updated demonstrative examples

Eric Dalci
Cigital
2008-07-01
updated Potential_Mitigations, Time_of_Introduction

CWE Content Team
MITRE
2008-09-08
updated Description, Relationships, Other_Notes, Taxonomy_Mappings

CWE Content Team
MITRE
2009-01-12
updated Relationships

CWE Content Team
MITRE
2009-07-27
updated Potential_Mitigations

CWE Content Team
MITRE
2009-10-29
updated Common_Consequences, Demonstrative_Examples, Description, Other_Notes, Relationship_Notes, Theoretical_Notes

CWE Content Team
MITRE
2010-04-05
updated Related_Attack_Patterns

CWE Content Team
MITRE
2010-12-13
updated Description

CWE Content Team
MITRE
2011-03-29
updated Potential_Mitigations

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

CWE Content Team
MITRE
2011-06-27
updated Common_Consequences

CWE Content Team
MITRE
2012-05-11
updated Demonstrative_Examples, References, Relationships

CWE Content Team
MITRE
2014-07-30
updated Relationships

CWE Content Team
MITRE
2015-12-07
updated Relationships

CWE Content Team
MITRE
2017-11-08
updated Applicable_Platforms, Demonstrative_Examples, Modes_of_Introduction, Relationships

CWE Content Team
MITRE
2019-01-03
updated Related_Attack_Patterns

CWE Content Team
MITRE
2019-06-20
updated Related_Attack_Patterns, Relationships

CWE Content Team
MITRE
2020-02-24
updated Potential_Mitigations, Relationships

CWE Content Team
MITRE
2020-06-25
updated Potential_Mitigations

CWE Content Team
MITRE
2021-10-28
updated Relationships

CWE Content Team
MITRE
2023-04-27
updated Detection_Factors, Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Applicable_Platforms, Relationships, Weakness_Ordinalities

Web Parameter Tampering