External Control of Assumed-Immutable Web Parameter
Weakness ID: 472 (Weakness Base)Status: Draft
+ Description

Description Summary

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. Failure to validate portions 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.

+ Alternate Terms
Assumed-Immutable Parameter Tampering
+ Time of Introduction
  • Implementation
+ Applicable Platforms



+ Common Consequences

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.

+ Demonstrative Examples

Example 1

Here, 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 Code)
Example Language: Java 
String accountID = request.getParameter("accountID");
User user = getUserFromID(Long.parseLong(accountID));

Example 2

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.

+ Observed Examples
CVE-2002-0108Forum product allows spoofed messages of other users via hidden form fields for name and e-mail address.
CVE-2000-0253Shopping cart allows price modification via hidden form field.
CVE-2000-0254Shopping cart allows price modification via hidden form field.
CVE-2000-0926Shopping cart allows price modification via hidden form field.
CVE-2000-0101Shopping cart allows price modification via hidden form field.
CVE-2000-0102Shopping cart allows price modification via hidden form field.
CVE-2000-0758Allows admin access by modifying value of form field.
CVE-2002-1880Read messages by modifying message ID parameter.
CVE-2000-1234Send email to arbitrary users by modifying email parameter.
CVE-2005-1652Authentication bypass by setting a parameter.
CVE-2005-1784Product does not check authorization for configuration change admin script, leading to password theft via modified e-mail address field.
CVE-2005-2314Logic error leads to password disclosure.
CVE-2005-1682Modification of message number parameter allows attackers to read other people's messages.
+ Potential Mitigations

Phase: Architecture and Design

Assume all input is malicious. Use a standard input validation mechanism to validate all input for length, type, syntax, and business rules before accepting the data to be displayed or stored. Use an "accept known good" validation strategy. Input (specifically, unexpected CRLFs) that is not appropriate should not be processed into HTTP headers.

Use and specify a strong input/output encoding (such as ISO 8859-1 or UTF 8).

Do not rely exclusively on blacklist validation to detect malicious input or to encode output. There are too many variants to encode a character; you're likely to miss some variants.

Inputs should be decoded and canonicalized to the application's current internal representation before being validated. Make sure that your application does not decode the same input twice. Such errors could be used to bypass whitelist schemes by introducing dangerous inputs after they have been checked.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness BaseWeakness Base471Modification of Assumed-Immutable Data (MAID)
Development Concepts (primary)699
Research Concepts1000
ChildOfWeakness ClassWeakness Class642External Control of Critical State Data
Research Concepts (primary)1000
ChildOfCategoryCategory715OWASP Top Ten 2007 Category A4 - Insecure Direct Object Reference
Weaknesses in OWASP Top Ten (2007) (primary)629
ChildOfCategoryCategory722OWASP Top Ten 2004 Category A1 - Unvalidated Input
Weaknesses in OWASP Top Ten (2004) (primary)711
RequiredByCompound Element: CompositeCompound Element: Composite384Session Fixation
Research Concepts1000
CanFollowWeakness BaseWeakness Base656Reliance on Security through Obscurity
Research Concepts1000
+ Relationship Notes

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

+ Theoretical Notes

This is a technology-specific MAID problem.

+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERWeb Parameter Tampering
OWASP Top Ten 2007A4CWE More SpecificInsecure Direct Object Reference
OWASP Top Ten 2004A1CWE More SpecificUnvalidated Input
+ Related Attack Patterns
CAPEC-IDAttack Pattern Name
(CAPEC Version: 1.4)
31Accessing/Intercepting/Modifying HTTP Cookies
39Manipulating Opaque Client-based Data Tokens
+ Content History
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modification DateModifierOrganizationSource
2008-07-01Sean EidemillerCigitalExternal
added/updated demonstrative examples
2008-07-01Eric DalciCigitalExternal
updated Potential Mitigations, Time of Introduction
2008-09-08CWE Content TeamMITREInternal
updated Description, Relationships, Other Notes, Taxonomy Mappings
2009-01-12CWE Content TeamMITREInternal
updated Relationships
2009-07-27CWE Content TeamMITREInternal
updated Potential Mitigations
2009-10-29CWE Content TeamMITREInternal
updated Common Consequences, Demonstrative Examples, Description, Other Notes, Relationship Notes, Theoretical Notes
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Web Parameter Tampering