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IDOR

IDOR (Insecure Direct Object Reference) This type of Vulnerability can happens when a Web Server receives User-Supplied input to retrieve Objects Files - Data - Documents too much trust has been placed on the Input Data, and it is not Validated on the Server-Side to confirm the Requested Object belongs to the User requesting it.


Vulnerable URL Example

  • Changing the Order Number will allow us to see another Customer Order.
  • Changing the User ID will allow us to see another Customer Profile
┌────────────────────────────────────────────┐  ┌────────────────────────────────────────────────┐
| https://onlinestore.com/order/1234/invoice |  | http://online-service.com/profile?user_id=1305 |
└────────────────────────────────────────────┘  └────────────────────────────────────────────────┘
                       |                                               |
                       ▼                                               ▼
┌────────────────────────────────────────────┐  ┌────────────────────────────────────────────────┐
| https://onlinestore.com/order/1000/invoice |  | http://online-service.com/profile?user_id=1000 |
└────────────────────────────────────────────┘  └────────────────────────────────────────────────┘

IDORs In Encoded ID's​

When passing Data from page to page either by (POST Data - Query Strings - Cookies) Web Developers will often first take the Raw Data and ENCODE it. Encoding ensures that the receiving Web Server will be able to understand the contents.

Encoding changes binary data into an ASCII string commonly using the (a-z A-Z 0-9) and ( = ) character for Padding.


  • Decode - Tamper - Encode - Submit
┌──────────────┐    ┌───────────┐    ┌──────────┐    ┌──────────────┐
| eyJpZCI6MzB9 | -► | {"id":30} | -► | {"id":5} | -► | eyJpZCI6NX0= |
└──────────────┘    └───────────┘    └──────────┘    └──────────────┘

IDORs In Hashed ID's​

Hashed ID's are more complicated to deal with than Encoded. But they may follow a Predictable Pattern, such as being the Hashed version of the Integer Value.


  • MD5 HASH
    • The ID 123 would become 202cb962ac59075b964b07152d234b70 if MD5 Hashing were in use.
┌──────────────────────────────────┐    ┌─────┐
| 202cb962ac59075b964b07152d234b70 | -► | 123 |
└──────────────────────────────────┘    └─────┘

IDORs In Unpredictable ID's​

A method of IDOR detection is to create Two Accounts and Swap the ID Numbers between them. If we can view the other User content using their ID Number while still being Logged in with a Different Account or not Logged, we found an IDOR Vulnerability.


IDORs Location​

The Vulnerable Endpoint we are Targeting may not always be something we see in the Address Bar. It could be content our Browser loads in via an AJAX Request or something that we find referenced in a JavaScript File.

Sometimes Endpoints could have an Unreferenced Parameter that may have been of some use during development and got pushed to production.

We may notice a call to /user/details displaying our User Information [Authenticated through our Session]. But through an Attack known as Parameter Mining we Discover a Parameter called user_id that we can use to display other User's Information.


  • Parameter Mining
┌───────────────┐    ┌─────────┐    ┌───────────────────────────┐
| /user/details | -► | user_id | -► | /user/details?user_id=123 |
└───────────────┘    └─────────┘    └───────────────────────────┘