Fakecalls Android Malware Abuses Reliable Signing Key

Authored by Dexter Shin 

McAfee Cellular Analysis Staff discovered an Android banking trojan signed with a key utilized by reputable apps in South Korea final yr. By design, Android requires that every one functions should be signed with a key, in different phrases a keystore, to allow them to be put in or replaced. As a result of this key can solely be utilized by the developer who created it, an software signed with the identical key is assumed to belong to the identical developer. That’s the case of this Android banking trojan that makes use of this reputable signing key to bypass signature-based detection methods. And these banking trojans weren’t distributed on Google Play or official app shops till now. This risk had been disclosed to the firm that owns the reputable key final yr and the firm has taken precautions. The firm has confirmed that they’ve substituted the signing key and at the moment, all of their reputable apps are signed with a brand new signing key. 

Android malware utilizing a reputable signing key 

Whereas monitoring the Android banking trojan Fakecalls we discovered a pattern utilizing the identical signing key as a properlyrecognized app in Korea. This app is developed by a respected IT companies firm with in depth enterprisees throughout numerous sectors, together with however not restricted to IT, gaming, cost, and advertising. We confirmed that many of the malicious samples utilizing this key fake to be a financial institutioning app as they use the identical icon as the true banking apps. 

Determine 1. Malware and reputable app on Google Play 

Distribution technique and newest status 

Domains verified final August once we first found the samples are actually down. Nonetheless, we investigated URLs associated to this malware and we discovered related ones associated to this risk. Amongst them, we recognized a phishing website that is nonetheless alive throughout our analysis. The location can be disguised as a banking website. 

Determine 2. A phishing web page disguised as a Korean banking website 

We additionally discovered that they up to date the area data of this internet web page a number of days earlier than our investigation. 

So we took a deeper look into this area and we discovered extra uncommon IP addresses that led us to the Command and control(C2) server admin pages utilized by the cybercriminals to manage the contaminated gadgets. 


Determine 3. Fakecalls Command and management(C2) admin web pages 

How does it work 

When we examine the APK file construction, we will see that this malware makes use of a packer to keep away from evaluation and detection. The malicious code is encrypted in one of many information beneath. 

Determine 4. Tencent’s Legu Packer libraries 

After decrypting the DEX file, we discovered some uncommon performance. The code beneath will get the Android bundle data from a file with a HTML extension. 

 Determine 5. Questionable code within the decrypted DEX file 

This file is in truth one other APK (Android Software) moderately than a conventional HTML file designed to be displayed in an online browser. 

Determine 6. APK file disguised as an HTML file 

When the person launches the malware, it instantly asks for permission to put in one other app. Then it tries to put in an software saved in the property listing as introduction.html”. Theintroduction.html” is an APK file and actual malicious conduct occurs right here. 

Determine 7. Dropper asks you to put in the principle payload 

When the dropped payload is about to be put in, it asks for a number of permissions to entry delicate private data. 

Determine 8. Permissions required by the principle malicious software 

It additionally registers a number of companies and receivers to manage notifications from the system and to obtain instructions from a distant Command and Management server. 

 Determine 9. Companies and receivers registered by the principle payload

Against this, the malware makes use of a reputable push SDK to obtain commands from a distant server. Listed below are the full listing of instructions and their goal. 


Command title  Function 
observe  sms message add 
incoming_transfer  caller quantity add 
del_phone_record  delete name log 
zhuanyi  set name forwarding with parameter 
clear_note  delete sms message 
assign_zhuanyi  set name forwarding 
file  file add 
lanjie  block sms message from specified numbers 
allfiles  discover all doable information and add them 
email_send  ship e-mail 
record_telephone  name recording on 
inout  re-mapping on C2 server 
blacklist  register as blacklist 
listener_num  no operate 
no_listener_num  disable monitoring a particular quantity 
rebuild  reset and reconnect with C2 
deleteFile  delete file 
num_address_list  contacts add 
addContact  add contacts 
all_address_list  name file add 
deleteContact  delete contacts 
note_intercept  intercept sms message from specified numbers 
intercept_all_phone  intercept sms message from all 
clear_date  delete all file 
clear_phone_contact  delete all contacts 
clear_phone_record  delete all name log 
per_note  fast sms message add 
soft_name  app title add 


Cybercriminals are continuously evolving and utilizing new methods to bypass safety checks, akin to abusing reputable signing keys. Fortuitously, there was no injury to customers as a result of this signing key leak. Nonetheless, we advocate that customers set up safety software program on their gadgets to answer these threats. Additionally, customers are beneficial to obtain and use apps from the official app shops. 

McAfee Cellular Safety detects this risk as Android/Banker whatever the software, is signed with the beforehand reputable signing key. 


Indicators of Compromise 


SHA256  Identify  Kind 
7f4670ae852ec26f890129a4a3d3e95c079f2f289e16f1aa089c86ea7077b3d8  신한신청서  Dropper 
9e7c9b04afe839d1b7d7959ad0092524fd4c6b67d1b6e5c2cb07bb67b8465eda  신한신청서  Dropper 
21ec124012faad074ee1881236c6cde7691e3932276af9d59259df707c68f9dc  신한신청서  Dropper 
9621d951c8115e1cc4cf7bd1838b8e659c7dea5d338a80e29ca52a8a58812579  신한신청서  Dropper 
60f5deb79791d2e8c2799e9af52adca5df66d1304310d1f185cec9163deb37a2  보안인증서  Banker 
756cffef2dc660a241ed0f52c07134b7ea7419402a89d700dffee4cc6e9d5bb6  보안인증서  Banker 
6634fdaa22db46a6f231c827106485b8572d066498fc0c39bf8e9beb22c028f6  보안인증서  Banker 
52021a13e2cd7bead4f338c8342cc933010478a18dfa4275bf999d2bc777dc6b  보안인증서  Banker 
125772aac026d7783b50a2a7e17e65b9256db5c8585324d34b2e066b13fc9e12  보안인증서  Banker 
a320c0815e09138541e9a03c030f30214c4ebaa9106b25d3a20177b5c0ef38b3  보안인증서  Banker 
c7f32890d6d8c3402601743655f4ac2f7390351046f6d454387c874f5c6fe31f  보안인증서  Banker 
dbc7a29f6e1e91780916be66c5bdaa609371b026d2a8f9a640563b4a47ceaf92  보안인증서  Banker 
e6c74ef62c0e267d1990d8b4d0a620a7d090bfb38545cc966b5ef5fc8731bc24  보안인증서  Banker 



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