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

 
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. 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.

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

Languages

All

+ Common Consequences
ScopeEffect

Technical Impact: 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.

+ 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:

(Bad Code)
Example Language: HTML 
< 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
ReferenceDescription
Forum product allows spoofed messages of other users via hidden form fields for name and e-mail address.
Shopping cart allows price modification via hidden form field.
Shopping cart allows price modification via hidden form field.
Shopping cart allows price modification via hidden form field.
Shopping cart allows price modification via hidden form field.
Shopping cart allows price modification via hidden form field.
Allows admin access by modifying value of form field.
Read messages by modifying message ID parameter.
Send email to arbitrary users by modifying email parameter.
Authentication bypass by setting a parameter.
Product does not check authorization for configuration change admin script, leading to password theft via modified e-mail address field.
Logic error leads to password disclosure.
Modification of message number parameter allows attackers to read other people's messages.
+ Potential Mitigations

Phase: Implementation

Strategy: Input Validation

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a whitelist 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 (i.e., do not rely on a blacklist). A blacklist 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, blacklists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

Phase: Implementation

Strategy: 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 whitelist validation 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
ChildOfCategoryCategory896SFP Cluster: Tainted Input
Software Fault Pattern (SFP) Clusters (primary)888
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 2007A4Insecure Direct Object Reference
OWASP Top Ten 2004A1Unvalidated Input
+ References
[REF-17] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 4: Use of Magic URLs, Predictable Cookies, and Hidden Form Fields." Page 75. McGraw-Hill. 2010.
[REF-7] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 17, "Embedding State in HTML and URLs", Page 1032.. 1st Edition. Addison Wesley. 2006.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
Externally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01CigitalExternal
added/updated demonstrative examples
2008-07-01CigitalExternal
updated Potential_Mitigations, Time_of_Introduction
2008-09-08MITREInternal
updated Description, Relationships, Other_Notes, Taxonomy_Mappings
2009-01-12MITREInternal
updated Relationships
2009-07-27MITREInternal
updated Potential_Mitigations
2009-10-29MITREInternal
updated Common_Consequences, Demonstrative_Examples, Description, Other_Notes, Relationship_Notes, Theoretical_Notes
2010-04-05MITREInternal
updated Related_Attack_Patterns
2010-12-13MITREInternal
updated Description
2011-03-29MITREInternal
updated Potential_Mitigations
2011-06-01MITREInternal
updated Common_Consequences
2011-06-27MITREInternal
updated Common_Consequences
2012-05-11MITREInternal
updated Demonstrative_Examples, References, Relationships
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Web Parameter Tampering
Page Last Updated: June 23, 2014