Android/TimpDoor Turns Mobile Devices Into Hidden Proxies

The McAfee Mobile Research team recently found an active phishing campaign using text messages (SMS) that tricks users into downloading and installing a fake voice-message app which allows cybercriminals to use infected devices as network proxies without users’ knowledge. If the fake application is installed, a background service starts a Socks proxy that redirects all …

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The McAfee Mobile Research team recently found an active phishing campaign using text messages (SMS) that tricks users into downloading and installing a fake voice-message app which allows cybercriminals to use infected devices as network proxies without users’ knowledge. If the fake application is installed, a background service starts a Socks proxy that redirects all network traffic from a third-party server via an encrypted connection through a secure shell tunnel—allowing potential access to internal networks and bypassing network security mechanisms such as firewalls and network monitors. McAfee Mobile Security detects this malware as Android/TimpDoor.

Devices running TimpDoor could serve as mobile backdoors for stealthy access to corporate and home networks because the malicious traffic and payload are encrypted. Worse, a network of compromised devices could also be used for more profitable purposes such as sending spam and phishing emails, performing ad click fraud, or launching distributed denial-of-service attacks.

Based on our analysis of 26 malicious APK files found on the main distribution server, the earliest TimpDoor variant has been available since March, with the latest APK from the end of August. According to our telemetry data, these apps have infected at least 5,000 devices. The malicious apps have been distributed via an active phishing campaign via SMS in the United States since at least the end of March. McAfee notified the unwitting hosts of the phishing domains and the malware distribution server; at the time of writing this post we have confirmed that they are no longer active.

Campaign targets North America

Since at least the end of March users in the United States have reported suspicious text messages informing them that they have two voice messages to review and tricking them into clicking a URL to hear them:

Figure 1. User reporting a text that required downloading a fake voice app. Source 800notes.com.

Figure 2. An August 9 text. Source: findwhocallsyou.com.

Figure 3. An August 26 text. Source: 800notes.com.

If the user clicks on one of these links in a mobile device, the browser displays a fake web page that pretends to be from a popular classified advertisement website and asks the user to install an application to listen to the voice messages:

Figure 4. A fake website asking the user to download a voice app.

In addition to the link that provides the malicious APK, the fake site includes detailed instructions on how to disable “Unknown Sources” to install the app that was downloaded outside Google Play.

Fake voice app

When the user clicks on “Download Voice App,” the file VoiceApp.apk is downloaded from a remote server. If the victim follows the instructions, the following screens appear to make the app look legitimate:

Figure 5. Fake voice app initial screens.

The preceding screens are displayed only if the Android version of the infected device is 7.1 or later (API Level 25). If the Android version is earlier, the app skips the initial screens and displays the main fake interface to listen to the “messages”:

Figure 6. The main interface of the fake voice messages app.

Everything on the main screen is fake. The Recents, Saved, and Archive icons have no functionality. The only buttons that work play the fake audio files. The duration of the voice messages does not correspond with the length of the audio files and the phone numbers are fake, present in the resources of the app.

Once the user listens to the fake messages and closes the app, the icon is hidden from the home screen to make it difficult to remove. Meanwhile, it starts a service in the background without user’s knowledge:

Figure 7. Service running in the background.

Socks proxy over SSH

As soon as the service starts, the malware gathers device information: device ID, brand, model, OS version, mobile carrier, connection type, and public/local IP address. To gather the public IP address information, TimpDoor uses a free geolocation service to obtain the data (country, region, city, latitude, longitude, public IP address, and ISP) in JSON format. In case the HTTP request fails, the malware make an HTTP request to the webpage getIP.php of the main control server that provides the value “public_ip.”

Once the device information is collected, TimpDoor starts a secure shell (SSH) connection to the control server to get the assigned remote port by sending the device ID. This port will be later used for remote port forwarding with the compromised device acting as a local Socks proxy server. In addition to starting the proxy server through an SSH tunnel, TimpDoor establishes mechanisms to keep the SSH connection alive such as monitoring changes in the network connectivity and setting up an alarm to constantly check the established SSH tunnel:

Figure 8. An execution thread checking changes in connectivity and making sure the SSH tunnel is running.

To ensure the SSH tunnel is up, TimpDoor executes the method updateStatus, which sends the previously collected device information and local/public IP address data to the control server via SSH.

Mobile malware distribution server

By checking the IP address 199.192.19[.]18, which hosted VoiceApp.apk, we found more APK files in the directory US. This likely stands for United States, considering that the fake phone numbers in the voice app are in the country and the messages are sent from US phone numbers:

Figure 9. APK files in the “US” folder of the main malware distribution server.

According to the “Last modified” dates on the server, the oldest APK in the folder is chainmail.apk (March 12) while the newest is VoiceApp.apk (August 27) suggesting the campaign has run for at least five months and is likely still active.

We can divide the APK files into two groups by size (5.1MB and 3.1MB). The main difference between them is that the oldest use an HTTP proxy (LittleProxy) while the newest (July and August) use a Socks proxy (MicroSocks), which allows the routing of all traffic for any kind of network protocol (not only HTTP)TTp on any port. Other notable differences are the package name, control server URLs, and the value of appVersion in the updateStatus method—ranging from 1.1.0 to 1.4.0.

In addition to the US folder we also found a CA folder, which could stand for Canada.

Figure 10. The “CA” folder on the distribution server.

Checking the files in the CA folder we found that VoiceApp.apk and relevanbest.apk are the same file with appVersion 1.4.0 (Socks proxy server). Octarineiads.apk is version 1.1.0, with an HTTP proxy.

TimpDoor vs MilkyDoor

TimpDoor is not the first malware that turns Android devices into mobile proxies to forward network traffic from a control server using a Socks proxy though an SSH tunnel. In April 2017 researchers discovered MilkyDoor, an apparent successor of DressCode, which was found a year earlier. Both threats were distributed as Trojanized apps in Google Play. DressCode installs only a Socks proxy server on the infected device; MilkyDoor also protects that connection to bypass network security restrictions using remote port forwarding via SSH, just as TimpDoor does. However, there are some relevant differences between TimpDoor and MilkyDoor:

  • Distribution: Instead of being part of a Trojanized app in Google Play, TimpDoor uses a completely fake voice app distributed via text message
  • SSH connection: While MilkyDoor uploads the device and IP address information to a control server to receive the connection details, TimpDoor already has the information in its code. TimpDoor uses the information to get the remote port to perform dynamic port forwarding and to periodically send updated device data.
  • Pure proxy functionality: MilkyDoor was apparently an adware integrator in early versions of the SDK and later added backdoor functionality. TimpDoor’s sole purpose (at least in this campaign) is to keep the SSH tunnel open and the proxy server running in the background without the user’s consent.

MilkyDoor seems to be a more complete SDK, with adware and downloader functionality. TimpDoor has only basic proxy functionality, first using an HTTP proxy and later Socks.

Conclusion

TimpDoor is the latest example of Android malware that turns devices into mobile backdoors—potentially allowing cybercriminals encrypted access to internal networks, which represents a great risk to companies and their systems. The versions found on the distribution server and the simple proxy functionality implemented in them shows that this threat is probably still under development. We expect it will evolve into new variants.

Although this threat has not been seen on Google Play, this SMS phishing campaign distributing TimpDoor shows that cybercriminals are still using traditional phishing techniques to trick users into installing malicious applications.

McAfee Mobile Security detects this threat as Android/TimpDoor. To protect yourselves from this and similar threats, employ security software on your mobile devices and do not install apps from unknown sources.

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Intercepter-NG – Android App For Hacking

Intercepter-NG is a multi functional network toolkit including an Android app for hacking, the main purpose is to recover interesting data from the network stream and perform different kinds of MiTM attacks.

Specifically referring to Intercepter-NG Co…

Intercepter-NG – Android App For Hacking

Intercepter-NG is a multi functional network toolkit including an Android app for hacking, the main purpose is to recover interesting data from the network stream and perform different kinds of MiTM attacks.

Specifically referring to Intercepter-NG Console Edition which works on a range of systems including NT, Linux, BSD, MacOSX, IOS and Android.

The Windows version is the one with the most powerful feature-set, but the Android app is fairly handy too.

Read the rest of Intercepter-NG – Android App For Hacking now! Only available at Darknet.

Google Play Users Risk a Yellow Card With Android/FoulGoal.A

English soccer fans have enthusiastically enjoyed the team’s current run in the World Cup, as the tune “Three Lions” plays in their heads, while hoping to end 52 years of hurt. Meanwhile a recent spyware campaign distributed on Google Play has hurt fan…

English soccer fans have enthusiastically enjoyed the team’s current run in the World Cup, as the tune “Three Lions” plays in their heads, while hoping to end 52 years of hurt. Meanwhile a recent spyware campaign distributed on Google Play has hurt fans of the beautiful game for some time. Using major events as social engineering is nothing new, as phishing emails have often taken advantage of disasters and sporting events to lure victims.

“Golden Cup” is the malicious app that installs spyware on victims’ devices. It was distributed via Google Play, and “offered” the opportunity to stream games and search for records from the current and past World Cups. McAfee Mobile Security identifies this threat as Android/FoulGoal.A; Google has removed the malicious applications from Google Play.

Once Golden Cup is installed it appears to be a typical sporting app, with multimedia content and general information about the event. Most of this data comes from a web service without malicious activity. However, in the background and without user consent the app silently transfers information to another server.

Data captured

Golden Cup captures a considerable amount of encrypted data from the victim’s device:

  • Phone number
  • Installed packages
  • Device model, manufacturer, serial number
  • Available internal storage capacity
  • Device ID
  • Android version
  • IMEI, IMSI

This spyware may be just the first stage of a greater infection due to its capability to load dex files from remote sources. The app connects to its control server and tries to download, unzip, and decrypt a second stage.

Android/FoulGoal.A detects when the screen is on or off and records this in its internal file scrn.txt, with the strings “on” or “off” to track when users are looking at their screens:

The Message Queuing Telemetry Transport protocol serves as the communication channel between the device and the malicious server to send and receive commands.

Data encryption

User data is encrypted with AES before it is sent to the control server. Cryptor class provides the encryption and decryption functionality. The doCrypto function is defined as a common function. As the first parameter of the function, “1” represents encryption and “2” is decryption mode:

The encryption key is generated dynamically using the SecureRandom function, which generates a unique value on the device to obfuscate the data. The addKey function embeds the encryption key into the encryption data. The data with the key is uploaded to the control server.

We believe the malware author uses this AES encryption technique for any information to be uploaded to escape the detection by Google Bouncer and network inspection products.

Our initial analysis suggests there were at least 300 infections, which we suspect occurred between June 8‒12, before the first World Cup matches began.

The second round

The second phase of the attack leverages an encrypted dex file. The file has a .data extension and is downloaded and dynamically loaded by the first-stage malware; it is extracted with the same mechanism used to upload the encrypted files. The location of the decryption key can be identified from the size of the contents and a fixed number in the first-stage malware.

After decryption, we can see out.dex in zipped format. The dex file has spy functions to steal SMS messages, contacts, multimedia files, and device location from infected devices.

The control server in second stage is different from the first stage’s. The encryption methodology and the server folder structures on the remote server are identical to the first stage.

We found one victim’s GPS location information and recorded audio files (.3gp) among the encrypted data on the control server.

Variants

We have also discovered two other variants of this threat created by the same authors and published to Google Play as dating apps. Although all the apps have been removed from Google Play, we still see indications of infections from our telemetry data, so we know these apps are active on some users’ devices.

Our telemetry data indicates that although users around the world have downloaded the app, the majority of downloads took place in the Middle East, most likely as a result of a World Cup–themed Twitter post in Hebrew directing people to download the app for a breakdown of the latest events.

McAfee Mobile Security users are protected against all the variants of this threat, detected as   Android/FoulGoal.A.

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AsiaHitGroup Returns With New Billing-Fraud Campaign

Are you tired yet of the music track “Despacito”? If you downloaded this ringtone app from Google Play, chances are your answer is a resounding Yes. But it gets worse: The McAfee Mobile Research team recently found 15 apps on Google Play that were uplo…

Are you tired yet of the music track “Despacito”? If you downloaded this ringtone app from Google Play, chances are your answer is a resounding Yes. But it gets worse: The McAfee Mobile Research team recently found 15 apps on Google Play that were uploaded by the AsiaHitGroup Gang. The ringtone app was one of them—downloaded 50,000 times from the official app store—that were designed to steal money from their victims. The AsiaHitGroup Gang has been active since at least 2016, attempting to charge 20,000 victims for the download of popular mobile applications containing the fake-installer app Sonvpay.A. For more analysis, see the Mobile Research team’s post.

Ordinarily we advise users to review the requested permissions before installing a mobile app, and normally this is enough. In this case, the only permission requested was access to SMS messages, and once installed the app behaved as expected. In the background, however, Sonvpay silently used the push notification service to subscribe users to premium-rate services.

This campaign displays a significant level of customization. The criminals can tailor their fraud to the country of their choosing. In our analysis we looked at mobile billing fraud targeting users in Kazakhstan, Malaysia, and Russia. In Kazakhstan victims are subscribed to a premium-rate service whereas in Malaysia and Russia they are connected to a WAP billing service. Further, the criminals recognize that in Malaysia the mobile operator sends a PIN code, so the attackers include functionality to intercept the SMS. Once intercepted, the app communicates with the mobile operator to subscribe to the service.

This group began targeting users in Asia, but the move to Russia shows its increasing ambition. The goal of the AsiaHitGroup Gang remains the same, but the manner in which they attempt to achieve their ends differs per campaign, and their techniques are improving. Although the security industry focuses much attention on “loud” and destructive attacks, many campaigns quietly steal funds from unsuspecting victims or those who have little visibility into what is happening.

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