Thursday, March 01, 2007

Session State Protection and URL Tampering in ApEx

For the third night in a row I'm working on my whitepaper "APEX by Example: Shared Components" for the IOUG Collaborate 07 conference. I need to upload it tomorrow, so no time to loose! Nevertheless I wanted to blog about URL Tampering, which I was investigating when I came to "Session State Protection" in the Shared Components area of ApEx.

For the moment I described it like this in my whitepaper (comments to make it better are welcome):

Session State Protection

Enabling Session State Protection can prevent hackers from tampering with the URLs within your application. URL tampering can adversely affect program logic, session state contents, and information privacy.

In DG Tournament


Why?

For security reasons! URL Tampering - Web based applications, including those developed in Oracle Application Express often pass values from one page to another through a URL. A clever enough user may observe this and override a value by typing his own value in the location field of his browser. For example in DG Tournament, when logged in as Admin, I can see a list of all users. When I click on that user for his details I see the same screen as a normal user would see in the “Your Profile” page. The URL that’s doing that call looks like this:

f?p=103:10:240848379705417::NO::P10_USER_ID:70

My application is 103, on page 10 with session id 240848379705417 (my session has a unique nr) you see at the end: P10_USER_ID:70 which means that my record (Dimitri Gielis) is user_id 70. By putting this in the url, the session knows about this value.
When “Session State Protection” is disabled you can easily see another user by changing the url to

f?p=103:10:240848379705417::NO::P10_USER_ID:71

This will give me the record (user) with user_id 71, without passing through the application I can obtain other information.
When “Session State Protection” is enabled you get a message like on the above screenshot, which tells you that the session state protection is violated.

How?

  1. At the moment the Session State Protection is disabled.


  2. To enable, disable, or configure Session State Protection using a wizard, click Set Protection.


  3. Click the Enable Session State Protection button


  4. We can see that the Session State Protection is now Enabled


  5. By clicking on the Page button you get following screen


  6. Select the page you want to protect, in DG Tournament for ex. User Detail and change the Page Access Protection.You can also go onto Item level to set the protections.


  7. That will add to the end of the url a checksum. An example of the previous url, but protected:
    f?p=103:10:240848379705417::NO::P10_USER_ID:70&cs=3831E8EB498FF406064BE08337E72A9DF When you try to change the user_id from 70 to 71 you get a message that the session state protection is violated.

6 comments:

Dimitri Gielis said...

BTW My goal isn't to be complete in any way. I just want to show the shared components in a real environment and how I used a specific Shared Component in DG Tournament.

Anonymous said...

Adding a checksum to an URL to prevent URL tampering was already described in a book... In the last century! There are quite some messages on Usenet archives too (groups.google.com on "url tampering") dating from easily more than five years ago. Ideally you'll also want to add some random value to your URL like, say, a cryptographic salt.

titti said...

how is this checksum calculated?

Anonymous said...

Thank you for all your insight. I have a slight problem. I am performing authentication through a database package. It works. Problem is, once a user signs in and goes to a page in the application, they can bypass the login page by bookmarking other pages in the application. How do I prevent that?

Dee Bee said...

Thank you for all your insight. I have a slight problem. I am performing authentication through a database package. It works. Problem is, once a user signs in and goes to a page in the application, they can bypass the login page by bookmarking other pages in the application. How do I prevent that?

p.s. Same msg on here 2X.

Anonymous said...

This prevent tampering only in item level if i change page id or application id page redirects