FirstBlood-#260[COLLAB] Query appointment with simple ID / Bypass front end restriction
This issue was discovered on FirstBlood v1

On 2021-05-15, jomar Level 4 reported:


Hello :)
As for the other reports this one is created in collaboration with Serizao.

I had initially not submitted this report because I thought it was the same root cause as report #46, but after a second check there is one thing that differs and so I created a new report.

However, if you look at the code of the page /yourappointments.php you can see this piece of javascript code:

The circled part corresponds to a small client-side check to verify that the submitted ID contains a pull, it sort of verifies that it matches the expected format, i.e. something like XXX-XXX-XXX-XXX

However, if we play the request directly into burp suite, this check will not be performed and it is therefore possible to submit anything. At this point an XHR query will be performed and will display the response if it is valid otherwise "Invalid appoitment ID!"

It is therefore also possible to submit here the reservation number with a simple ID which will be mapped to its complex equivalent.

For ex, the simple ID 56911356 correspond to the complexe ID cef4d2e6-a63b-40aa-bcfa-246bef277374.


  • It is therefore possible to access another user's reservation by iterating on the ID and also to modify/cancel his reservation.
  • With this bug, it is also possible to obtain the stored XSS through the message parameter on the admin panel via the reservation of another user (cf bug #208


  • Do not limit yourself to a client-side verification and also perform a server-side verification
  • Try to use as much complex IDs (GUID) as possible as in the user part and do not map between a "simple" ID and a "complex" ID
  • If possible add a second factor to validate that the reservation belongs to the user (such as validating the date of birth)
  • Set up a system of request limit or captcha (recaptchav3 for example) in order to limit abusive requests

P2 High

Endpoint: /api/qa.php

Parameter: id=

Payload: id=56911356

FirstBlood ID: 5
Vulnerability Type: Insecure direct object reference

The endpoint QA.php (to query for an appointment) will allow for integer values to be used when querying for appointments. A bad cause of security through obscurity was attempted.