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CWE
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Authorization Bypass Through User-Controlled Key

ID: 639Date: (C)2012-05-14   (M)2019-10-11
Type: weaknessStatus: INCOMPLETE
Abstraction Type: Base





Description

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.

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.

Likelihood of Exploit: High

Applicable Platforms
Language Class: Language-independent

Time Of Introduction

  • Architecture and Design

Common Consequences

ScopeTechnical ImpactNotes
Access_Control
 
Bypass protection mechanism
 
Access control checks for specific user data or functionality can be bypassed.
 
Access_Control
 
Gain privileges / assume identity
 
Horizontal escalation of privilege is possible (one user can view/modify information of another user).
 
Access_Control
 
Gain privileges / assume identity
 
Vertical escalation of privilege is possible if the user controlled key is actually an admin flag allowing to gain administrative access.
 

Detection Methods
None

Potential Mitigations

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

Related CWETypeViewChain
CWE-639 ChildOf CWE-899 Category CWE-888  

Demonstrative Examples
None

White Box Definitions
None

Black Box Definitions
None

Taxynomy Mappings
None

References:
None

CVE    22
CVE-2017-15199
CVE-2017-15197
CVE-2017-15196
CVE-2017-15195
...

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