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.
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. 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. One manifestation of this weakness is when a system uses 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.
IDOR Vulnerability Writeup
Read our in-depth guide on exploiting and mitigating this weakness
Potential Impact
Access Control
Bypass Protection Mechanism
Access Control
Gain Privileges or Assume Identity
Access Control
Gain Privileges or Assume Identity
Demonstrative Examples
...
conn = new SqlConnection(_ConnectionString);
conn.Open();
int16 id = System.Convert.ToInt16(invoiceID.Text);
SqlCommand query = new SqlCommand( "SELECT * FROM invoices WHERE id = @id", conn);
query.Parameters.AddWithValue("@id", id);
SqlDataReader objReader = objCommand.ExecuteReader();
...Mitigations & Prevention
For each and every data access, ensure that the user has sufficient privilege to access the record that is being requested.
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.
Detection Methods
- Automated Static Analysis High — Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then sea
Real-World CVE Examples
| CVE ID | Description |
|---|---|
| CVE-2021-36539 | An educational application does not appropriately restrict file IDs to a particular user. The attacker can brute-force guess IDs, indicating IDOR. |
Related Weaknesses
Frequently Asked Questions
What is CWE-639?
CWE-639 (Authorization Bypass Through User-Controlled Key) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Base-level weakness. 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.
How can CWE-639 be exploited?
Attackers can exploit CWE-639 (Authorization Bypass Through User-Controlled Key) to bypass protection mechanism. This weakness is typically introduced during the Architecture and Design phase of software development.
How do I prevent CWE-639?
Key mitigations include: For each and every data access, ensure that the user has sufficient privilege to access the record that is being requested.
What is the severity of CWE-639?
CWE-639 is classified as a Base-level weakness (Medium abstraction). It has been observed in 1 real-world CVEs.