CWE-639: Authorization Bypass Through User-Controlled Key
Authorization Bypass Through User-Controlled Key
Weakness ID: 639 (Weakness Base)
Status: Incomplete
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
Languages
Language-independent
Common Consequences
Scope
Effect
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
High
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.
Description
