Common Weakness Enumeration

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CWE-639: Authorization Bypass Through User-Controlled Key

Weakness ID: 639
Abstraction: Base
Status: Incomplete
Presentation Filter:
+ Description

Description Summary

The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.

Extended Description

Retrieval of a user record occurs in the system based on some key value that is under user control. The key would typically identify a user related record stored in the system and would be used to lookup that record for presentation to the user. It is likely that an attacker would have to be an authenticated user in the system. However, the authorization process would not properly check the data access operation to ensure that the authenticated user performing the operation has sufficient entitlements to perform the requested data access, hence bypassing any other authorization checks present in the system. One manifestation of this weakness would be if a system used sequential or otherwise easily guessable session ids that would allow one user to easily switch to another user's session and read/modify their data.

+ Alternate Terms
Insecure Direct Object Reference:

The "Insecure Direct Object Reference" term, as described in the OWASP Top Ten, is broader than this CWE because it also covers path traversal (CWE-22). Within the context of vulnerability theory, there is a similarity between the OWASP concept and CWE-706: Use of Incorrectly-Resolved Name or Reference.

Horizontal Authorization:

"Horizontal Authorization" is used to describe situations in which two users have the same privilege level, but must be prevented from accessing each other's resources. This is fairly common when using key-based access to resources in a multi-user context.

+ Time of Introduction
  • Architecture and Design
+ Applicable Platforms



+ Common Consequences
Access Control

Technical Impact: Bypass protection mechanism

Access control checks for specific user data or functionality can be bypassed.

Access Control

Technical Impact: Gain privileges / assume identity

Horizontal escalation of privilege is possible (one user can view/modify information of another user).

Access Control

Technical Impact: Gain privileges / assume identity

Vertical escalation of privilege is possible if the user-controlled key is actually a flag that indicates administrator status, allowing the attacker to gain administrative access.

+ Likelihood of Exploit


+ Enabling Factors for Exploitation

The key used internally in the system to identify the user record can be externally controlled. For example attackers can look at places where user specific data is retrieved (e.g. search screens) and determine whether the key for the item being looked up is controllable externally. The key may be a hidden field in the HTML form field, might be passed as a URL parameter or as an unencrypted cookie variable, then in each of these cases it will be possible to tamper with the key value.

+ Potential Mitigations

Phase: Architecture and Design

For each and every data access, ensure that the user has sufficient privilege to access the record that is being requested.

Phases: Architecture and Design; Implementation

Make sure that the key that is used in the lookup of a specific user's record is not controllable externally by the user or that any tampering can be detected.

Phase: Architecture and Design

Use encryption in order to make it more difficult to guess other legitimate values of the key or associate a digital signature with the key so that the server can verify that there has been no tampering.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory715OWASP Top Ten 2007 Category A4 - Insecure Direct Object Reference
Weaknesses in OWASP Top Ten (2007) (primary)629
ChildOfCategoryCategory723OWASP Top Ten 2004 Category A2 - Broken Access Control
Weaknesses in OWASP Top Ten (2004) (primary)711
ChildOfCategoryCategory813OWASP Top Ten 2010 Category A4 - Insecure Direct Object References
Weaknesses in OWASP Top Ten (2010) (primary)809
ChildOfCategoryCategory840Business Logic Errors
Development Concepts699
ChildOfWeakness ClassWeakness Class862Missing Authorization
Development Concepts (primary)699
Research Concepts (primary)1000
ChildOfCategoryCategory932OWASP Top Ten 2013 Category A4 - Insecure Direct Object References
Weaknesses in OWASP Top Ten (2013) (primary)928
ChildOfCategoryCategory945SFP Secondary Cluster: Insecure Resource Access
Software Fault Pattern (SFP) Clusters (primary)888
ParentOfWeakness VariantWeakness Variant566Authorization Bypass Through User-Controlled SQL Primary Key
Development Concepts (primary)699
Research Concepts (primary)1000
+ Content History
Submission DateSubmitterOrganizationSource
2008-01-30Evgeny LebanidzeCigitalExternal Submission
Modification DateModifierOrganizationSource
2008-09-08CWE Content TeamMITREInternal
updated Common_Consequences, Relationships, Type
2008-10-14CWE Content TeamMITREInternal
updated Description
2009-03-10CWE Content TeamMITREInternal
updated Relationships
2009-05-27CWE Content TeamMITREInternal
updated Relationships
2009-10-29CWE Content TeamMITREInternal
updated Common_Consequences
2010-06-21CWE Content TeamMITREInternal
updated Relationships
2011-03-29CWE Content TeamMITREInternal
updated Alternate_Terms, Applicable_Platforms, Description, Name, Potential_Mitigations, Relationships
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences, Relationships
2012-05-11CWE Content TeamMITREInternal
updated Relationships
2013-02-21CWE Content TeamMITREInternal
updated Alternate_Terms, Common_Consequences
2013-07-17CWE Content TeamMITREInternal
updated Relationships
2014-07-30CWE Content TeamMITREInternal
updated Relationships
Previous Entry Names
Change DatePrevious Entry Name
2011-03-29Access Control Bypass Through User-Controlled Key

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Page Last Updated: May 05, 2017