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Insecure Direct Object References
Insecure Direct Object References (IDOR) is a security vulnerability that occurs when an application allows users to directly access or modify objects (such as files, database records, or URLs) based on user-supplied input, without sufficient access controls. This means that if a user changes a parameter value (like an ID) in a URL or API request, they might be able to access or manipulate data that they aren’t authorized to see or modify.
Summary
Tools
- PortSwigger/BApp Store > Authz
- PortSwigger/BApp Store > AuthMatrix
- PortSwigger/BApp Store > Autorize
Methodology
IDOR stands for Insecure Direct Object Reference. It's a type of security vulnerability that arises when an application provides direct access to objects based on user-supplied input. As a result, attackers can bypass authorization and access resources in the system directly, potentially leading to unauthorized information disclosure, modification, or deletion.
Example of IDOR
Imagine a web application that allows users to view their profile by clicking a link https://example.com/profile?user_id=123
:
<?php
$user_id = $_GET['user_id'];
$user_info = get_user_info($user_id);
...
Here, user_id=123
is a direct reference to a specific user's profile. If the application doesn't properly check that the logged-in user has the right to view the profile associated with user_id=123
, an attacker could simply change the user_id
parameter to view other users' profiles:
https://example.com/profile?user_id=124
Numeric Value Parameter
Increment and decrement these values to access sensitive information.
- Decimal value:
287789
,287790
,287791
, ... - Hexadecimal:
0x4642d
,0x4642e
,0x4642f
, ... - Unix epoch timestamp:
1695574808
,1695575098
, ...
Examples
- HackerOne - IDOR to view User Order Information - meals
- HackerOne - Delete messages via IDOR - naaash
Common Identifiers Parameter
Some identifiers can be guessed like names and emails, they might grant you access to customer data.
- Name:
john
,doe
,john.doe
, ... - Email:
john.doe@mail.com
- Base64 encoded value:
am9obi5kb2VAbWFpbC5jb20=
Examples
Weak Pseudo Random Number Generator
- UUID/GUID v1 can be predicted if you know the time they were created:
95f6e264-bb00-11ec-8833-00155d01ef00
- MongoDB Object Ids are generated in a predictable manner:
5ae9b90a2c144b9def01ec37
- a 4-byte value representing the seconds since the Unix epoch
- a 3-byte machine identifier
- a 2-byte process id
- a 3-byte counter, starting with a random value
Examples
- HackerOne - IDOR allowing to read another user's token on the Social Media Ads service - a_d_a_m
- IDOR through MongoDB Object IDs Prediction
Hashed Parameter
Sometimes we see websites using hashed values to generate a random user id or token, like sha1(username)
, md5(email)
, ...
- MD5:
098f6bcd4621d373cade4e832627b4f6
- SHA1:
a94a8fe5ccb19ba61c4c0873d391e987982fbbd3
- SHA2:
9f86d081884c7d659a2feaa0c55ad015a3bf4f1b2b0b822cd15d6c15b0f00a08
Examples
Wildcard Parameter
Send a wildcard (*
, %
, .
, _
) instead of an ID, some backend might respond with the data of all the users.
GET /api/users/* HTTP/1.1
GET /api/users/% HTTP/1.1
GET /api/users/_ HTTP/1.1
GET /api/users/. HTTP/1.1
Examples
IDOR Tips
- Change the HTTP request:
POST → PUT
- Change the content type:
XML → JSON
- Transform numerical values to arrays:
{"id":19} → {"id":[19]}
- Use Parameter Pollution:
user_id=hacker_id&user_id=victim_id
Labs
References
- From Christmas present in the blockchain to massive bug bounty - Jesse Lakerveld - March 21, 2018
- How-To: Find IDOR (Insecure Direct Object Reference) Vulnerabilities for large bounty rewards - Sam Houton - November 9, 2017
- Hunting Insecure Direct Object Reference Vulnerabilities for Fun and Profit (PART-1) - Mohammed Abdul Raheem - February 2, 2018
- IDOR - how to predict an identifier? Bug bounty case study - Bug Bounty Reports Explained - September 21, 2023
- Insecure Direct Object Reference Prevention Cheat Sheet - OWASP - July 31, 2023
- Insecure direct object references (IDOR) - PortSwigger - December 25, 2019
- Testing for IDORs - PortSwigger - October 29, 2024
- Testing for Insecure Direct Object References (OTG-AUTHZ-004) - OWASP - August 8, 2014
- The Rise of IDOR - HackerOne - April 2, 2021
- Web to App Phone Notification IDOR to view Everyone's Airbnb Messages - Brett Buerhaus - March 31, 2017