Access Control Bypass Through User-Controlled Key
Weakness ID: 639 (Weakness Base)Status: Incomplete
+ Description

Description Summary

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

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 view/modify their data.

+ Time of Introduction
  • Architecture and Design
+ Applicable Platforms



+ Common Consequences
Access Control

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

Access Control

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


Vertical escalation of privilege is possible if the user controlled key is actually an admin flag allowing 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

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.

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..

Ensure that access control mechanisms cannot be bypassed by ensuring that the user has sufficient privilege to access the record that is being requested given his authenticated identity on each and every data access.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class284Access Control (Authorization) Issues
Development Concepts (primary)699
Research Concepts (primary)1000
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
ParentOfWeakness VariantWeakness Variant566Access Control 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