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CWE-639 Individual Dictionary Definition (Draft 9)
Weakness ID
| Status: Incomplete 639 (Weakness Variant) | | 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. 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. | | Likelihood of Exploit | High | | Common Consequences | Access control checks for specific user data or functionality can be bypassed. 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 | | 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 | | | Applicable Platforms | All | | Time of Introduction | Architecture and Design |
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- Weakness
- Base
- Variant
- Class
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- Composite
- Category
- View
- Deprecated
