Unpatched Android App with 1B Downloads Allows RCE

2021-02-16T14:08:04
ID THREATPOST:0C3F574DCF2CF781A74B1CCCE93146AD
Type threatpost
Reporter Elizabeth Montalbano
Modified 2021-02-16T14:08:04

Description

An Android app that’s been downloaded more than 1 billion times is riddled with flaws that can let attackers hijack app features or overwrite existing files to execute malicious code, or launch man-in-the-disk (MiTD) attacks on people’s devices, researchers discovered.

The flaws exist in an app called SHAREit, which allows Android app users to share files between friends or devices. They were identified and reported to the app maker three months ago by researchers at Trend Micro. However, the flaws remain unpatched, according to a report posted online Monday.

“We decided to disclose our research three months after reporting this since many users might be affected by this attack, because the attacker can steal sensitive data and do anything with the apps’ permission,” Echo Duan, a mobile threats analyst for Trend Micro, wrote in the report. “It is also not easily detectable.”

Trend Micro also notified Google of the app’s issues, which lie in several flaws in its code that too easily give third parties permissions to take over legitimate app features, overwrite existing app files or even take over Android storage shared by multiple apps to execute malicious code, he said.

SHAREit’s Bevy of Security Bugs

“We delved into the app’s code and found that it declares the broadcast receiver as ‘com.lenovo.anyshare.app.DefaultReceiver,'” Duan explained in the post. “It receives the action ‘com.ushareit.package.action.install_completed’ and Extra Intent then calls the startActivity() function.”

Researchers built a simple proof of concept (PoC) and found that “any app can invoke this broadcast component,” he said. “This shows arbitrary activities, including SHAREit’s internal (non-public) and external app activities.”

Moreover, third-parties also can gain temporary read/write access to the content provider’s data through a flaw in its FileProvider, Duan wrote. “Even worse, the developer specified a wide storage area root path,” he wrote. “In this case, all files in the /data/data/<package> folder can be freely accessed.”

In Trend Micro’s PoC, researchers included code that reads WebView cookies, which was used to write any files in the SHAREit app’s data folder. “In other words, it can be used to overwrite existing files in the SHAREit app,” Duan said of the attack.

In this way malicious apps installed on a device running SHAREit can run take over the app to run custom code or install third-party apps without the user knowing, researchers found.

Man-in-the-Disk Mobile Threat

SHAREit also is susceptible to an MiTD attack, a variation on a man-in-the-middle attack identified by Check Point in 2018 that arises from the way the Android OS uses two types of storage—internal and external, the latter of which uses a removable SD card and is shared across the OS and all apps.

This type of attack allows someone to intercept and potentially alter data as it moves between Android external storage and an installed app, and is possible using SHAREit “because when a user downloads the app in the download center, it goes to the directory,” Duan wrote. “The folder is an external directory, which means any app can access it with SDcard write permission.”

Researchers illustrated this action in their POC by manually copying Twitter.apk in the code to replace it with a fake file of the same name. As a result, a pop-up of the fake Twitter app appeared on the main screen of the SHAREit app, Duan wrote. Reopening SHAREit caused the fake Twitter app to appear on the screen again, prompting the user to install it, an action that is successful, according to the post.

Trend Micro’s discovery isn’t the first time serious flaws were found in SHAREit. Two years ago researchers discovered two high-severity flaws in the app that allowed an attacker to bypass the file transfer application’s device authentication mechanism and ultimately download content and arbitrary files from the victim’s device.

Duan recommended that people regularly update and patch mobile operating systems and the apps themselves to maintain security on their devices, as well as “keep themselves informed by reading reviews and articles about the apps they download.”

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