500 Million UC Browser Android Users are Vulnerable to Man-in-the-Middle Attacks

Researchers discovered various unusual activities in UC Browser for Android and it abusing the Google play policies and exposing more than 500  users to Man-in-the-Middle attacks.

UC browser is the most popular browser in the Android platform with more than 500 million users and UC Browser Mini has 100 million downloads from the Google Play store alone.

GBHackers on Security has been reported several UC browser-based incidents including malicious activities, vulnerabilities before and it is a very serious concern that needs to be addressed for any unusual behaviors since it will directly affect the hundreds of millions of users.

Recent research from Zscaler reveals that the UC Browser and UC Browser Mini apps unusually made a request over unprotected (HTTP) channel to download an additional Android Package Kit from the remote server.

There are 3 main unusual  activities found from  UC Browser app in this research :

1. Downloading an additional APK from a third party – in violation of Google Play policy
2. Communication over an unsecured channel – opening doors to man-in-the-middle attacks
3. Dropping an APK on external storage (/storage/emulated/0) – allowing other apps, with appropriate permissions, to tamper with the APK

Downloading an additional APK

After completing the installation process, researchers noticed that the app sending multiple requests and finally drop an APK on the user’s device.

The APK dropped into external storage but there is no sign of installation process. Researchers believe that the functionality is still under development

According to Google Play policy, Apps should not download and APK from any third-party source.

“An app distributed via Google Play may not modify, replace, or update itself using any method other than Google Play’s update mechanism. Likewise, an app may not download executable code (e.g., dex, JAR, .so files) from a source other than Google Play.”

Unsecured channel Communication

UC browsers download the APK from completely unencrypted communication that possibility open for man-in-the-middle (MiTM) attacks.

In March 2019, We have already reported a similar issue in which hidden future that uncovered in UC browsers let attackers download and run untested code in any of the Android devices and also its bypass the Google Play servers by downloading the auxiliary software modules that allow hackers to hijack Android devices via Man-in-the-Middle Attacks.

Researchers believe that “It could be that the same app had been uploaded again on Google Play with a different name and developer along with modified or enhanced code to download additional APKs.” 

Dropping an APK on external storage

An APK file that being by UC browser from the remote server is stored on external storage which is world-readable by default.

 “An APK being placed on external storage, or any other app with storage permission (android:name=android.permission.READ/WRITE_EXTERNAL_STORAGE) can have access to this location and can tamper with the downloaded APK.” 

Since there wasn’t any installation behavior, the researcher manually tried to install the downloaded APK file and find found that the APK was a third-party app store named “9 Apps.

Further analysis revealed that the 3rd Party app store distributing several adult apps. When we tried to download any app, it downloaded from 9appsdownloading[.]com

After Google’s intervention, the latest version of both the apps, UC Browser and UC Mini, has stopped downloading the third-party app store and the UC browser users are advised to update the latest version.

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