RCE Security Advisory
https://www.rcesecurity.com


1. ADVISORY INFORMATION
=======================
Product:        FC Red Bull Salzburg App
Vendor URL:     https://play.google.com/store/apps/details?id=laola.redbull
Type:           Improper Authorization in Handler for Custom URL Scheme [CWE-939]
Date found:     2023-04-06
Date published: 2023-06-01
CVSSv3 Score:   6.1 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N)
CVE:            CVE-2023-29459


2. CREDITS
==========
This vulnerability was discovered and researched by Julien Ahrens from
RCE Security.


3. VERSIONS AFFECTED
====================
FC Red Bull Salzburg App <= 5.1.9-R


4. INTRODUCTION
===============
Die FC Red Bull Salzburg-App bietet allen Fans innovative Features, die ein
modernes Stadionerlebnis ermöglichen.

Mit verschiedenen Livecams, die nur innerhalb der Red Bull Arena abrufbar
sind und das Spielgeschehen aus unterschiedlichen Perspektiven zeigen, sowie
auch Sofortwiederholungen aller wichtigen Szenen wird der Besuch in der Red
Bull Arena auf ein neues Level gehievt.

(from the vendor's homepage)


5. VULNERABILITY DETAILS
========================
The "FC Red Bull Salzburg App" app for Android exposes an activity called
"at.redbullsalzburg.android.AppMode.Default.Splash.SplashActivity".

This activity aims to show the contents of a given URL within the app's context.
However, the app does not properly validate the URL and the intent's data URI,
which an unauthenticated attacker can abuse to load arbitrary contents into the
app by either tricking the user into opening a specifically crafted link or using
a malicious app on the same device.

The specific problem here is the assumed trust between the user having the app
installed and what the app is actually doing/displaying to the user. So if the
user sees the app being loaded and automatically redirecting to another page, it
can be assumed that the user also trusts the loaded page.


6. PROOF OF CONCEPT
===================
There are two ways to exploit this vulnerability:

1. Via the app's custom URI scheme "fcrbs" followed by any arbitrary URL:
fcrbs://www.rcesecurity.com

2. Via an explicit intent invocation:
Intent i = new Intent();
i.setComponent(new ComponentName("laola.redbull", "at.redbullsalzburg.android.AppMode.Default.Splash.SplashActivity"));
i.setData(Uri.parse("https://www.rcesecurity.com"));
startActivity(i);


7. SOLUTION
===========
None. Uninstall the app.


8. REPORT TIMELINE
==================
2023-04-06: Discovery of the vulnerability
2023-04-06: RCE Security sends initial notification to vendor via security@redbull.com and to soc@redbull.com
2023-04-06: RCE Security asks Intigriti.com for a security contact because of a disagreement with Intigriti's disclosure terms
2023-04-06: Intigriti states that they don't hand out contact email addresses of customers
2023-04-06: MITRE assigns CVE-2023-29459
2023-04-07: Vendor responds stating to submit everything via Intigriti
2023-04-07: RCE Security asks for another way to report due to the unacceptable T&Cs of Intigriti
2023-04-11: Vendor responds stating that a report to soc@redbull.com is sufficient
2023-04-11: RCE Security provides a preliminary version of this advisory
2023-04-19: Vendor acknowledges the vulnerability
2023-04-19: RCE Security extends disclsoure date to its maxiumum of 45 days
2023-05-07: No Response from vendor
2023-05-07: RCE Security asks vendor for an update since disclosure date is coming
2023-05-11: No Response from vendor
2023-05-11: RCE Security asks vendor for an update
2023-05-12: Vendor response stating that more time is needed to fix the bug since the developers are not within the organization
2023-05-15: RCE Security reminds the vendor of the disclosure policy and date
2023-05-27: No response from vendor
2023-05-27: RCE Security sends one last notification and adjusted the disclosure date to 01st June 2023
2023-06-01: No response from vendor
2023-06-01: Public Disclosure


9. REFERENCES
=============
https://github.com/MrTuxracer/advisories
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-29459