How I almost caught a virus trying to sell my boots

I am one of those people who with the onset of autumn tries to spend less time on the street. In Moscow it is not difficult: you limit yourself to the route from home to office and back. However, the wet weather can cause discomfort in the room, especially if your workplace, like mine, is at the window, and every second colleague, complaining of stuffiness, asks to air the office. In order not to fall into a blues, I have updated my wardrobe this fall.

Reflecting on the fate of unnecessary things, I wondered what to do with them: throw it away, cut it into rags, give it to my younger brother? But for one thing, none of these methods did not suit: they were leather boots of 44 sizes of a decent look, but I was pretty tired. I decided to sell them on Avito. I uploaded photos, indicated a fake name (information security), put on boots, a couple of other things and went to sleep. How could I know that this would result in a lengthy analysis of the application for hidden threats?

A pleasant surprise

The next day, after a couple of dubious calls, I received an interesting SMS message with the following content:

A couple of days later I received another similar message:

Surprised that someone somehow could transfer me money via the Internet (apparently, I’m the old one I still use paper savings books), I clicked on the link in SMS.

After that I was offered to download an application for Android (apk-file). Happily downloading the file, I saw the following:

Causes confidence! I eagerly wanted to quickly install everything and get it over with.
But here, as usual, the annoying Android operating system for some reason prevented me from running the file. "Yes, give the money already!" - I was indignant. I had to go to the settings and turn on some option "Unknown sources", is the phone really that stupid in 2018? By the way, my phone is Xiaomi Remdi with Andoid 6.0.1 (note for techies).

This was followed by a chain of strange events. The phone continued to report inaccurate sources. But Avito is a reliable source ! I had to google, figure out how to get around this, and then disable it in the settings. Soon a certain antivirus appeared that I did not install.

Finally, I saw the cherished standard installation window - there is no point in looking at permissions in our time, now even the notebook will not start until you give him full access to the phone. Joyful moment of the end of the installation of the application and the START! I was looking forward to the promised money. Additionally, the application requested administrator privileges, with which I happily agreed. Unfortunately, the application behaved strangely and did not want to pay, and soon disappeared completely from the list of applications on the general screen.

Spoiler

Later I checked on another phone - Lenovo with Android 4.4.2 on board. The list of permissions during installation turned out to be much larger. And no Play Protection and Anti-Virus do not interfere, it is only necessary to allow installation from unreliable sources.

Altruism

So, what we have come to:

The installation took 20 minutes of time.
I did not get the money.

I thought that the problem was in the error code, as is often the case with programmers. I decided to identify the errors that occur when the application is running on my phone, and send a report about this to the developer.

Spoiler

Now there are so few unselfish people left, one of them is me.

It is clear that this type of application should work when the Internet is connected, so for a start I tried to analyze the traffic between the phone and the application server.

Technical instructions for setting up a proxy

Можно прослушать интернет-трафик в любой точке, проходящей по пути от телефона до сервера, будь то домашний роутер, местный интернет-провайдер, магистральный интернет-провайдер или сервер приложения.

Проблемы:

Необходим доступ к данному оборудованию.
Требуется отделить трафик нужного приложения от остального.
В случае шифрования (а в 2018 шифруется уже всё) — необходимо знание ключа.

Я задумал пройти более классическим путём и настроить прокси на телефоне с прокси сервером на собственном ноутбуке. Чтобы нивелировать проблему шифрования, решил импортировать свой сертификат, а для отделения трафика приложения не стал запускать другие приложения.
В качестве программы прокси-сервера выбрал burp suite. Настроил прокси-сервер и экспортировал сертификат на телефон.

After setting up the specialized software, I was able to see which requests the application sends to the server: As you can see, the data is not sent (the IP value is “unknown host”), moreover, they cannot be analyzed due to the presence of additional encryption at the application level . Judging by the error, the phone could not determine the IP address of the server and its subdomains https: //*.sky-sync.pw by its domain name. This could only mean the following options:

Domain name has ceased to exist
- It was blocked by the owner himself.
- He was blocked by the registrar of the complaint.
DNS server issue
- The DNS server does not know the address, as the developer in production rolled out the local DNS address.
- The DNS server specifically blocked this request, which is not surprising in the era of Internet censorship.

To check the assumption about the problem with the DNS server, I tried to make requests from various large DNS servers: Google, Yandex, OpenDNS (local DNS is usually censored):

Here you can see that none of them knows anything about such a name. Then I looked at the whois-domain registration information:

Curiously: the domain is registered, that is, most likely, it is not local, but since the domain is not resolved, it may have been blocked by the registrar on the complaint (abuse). But for what? What did he do wrong?

To find out what this is all about the application and how I can take my money, I decided to use the ~~magic of~~ reverse engineering.

Dive into the abyss

If you are a humanist and have read this far, then this is already good - for mastering the subsequent, you are worthy of the award ~~posthumously~~ .

Tools

To find out what is under the hood of the application, we need to download specialized tools. You can download them separately:

Apk-container unpacker
- Classic - ApkTool .
- You can unpack with a regular archiver, but then all binary resources, including applications and the Manifest file, will be unreadable.
Smali code decompiler
- The standard is Dex2Jar , but learn that this program often performs crookedly.
- It is necessary to approach the matter very carefully, because the decompiler to the decompiler is different, consider it later.
A program to view the decompiled code , I would recommend jd-gui

Or you can use the product, usually paid, where there is everything at once. I prefer JebDecompiler : it can simply send an apk-application to the input, and he will carefully arrange everything on tabs, plus it is convenient to switch between smali and decompiled Java code.

Separately, I want to note:

In the presence of native libs (the / libs folder in the application structure), a disassembler would be needed .
You may need a set of utilities for working with smali-code (dex-to-smali, smali-to-dex).
Syntax highlighting in Notepad ++, so as not to break the eyes.

Only old men go to battle

Overview

When you open the decompiled code, it becomes immediately clear that it is obfuscated.

How do I understand this?

Unreadable class names
isqpwcmx.isfdztgb.adscjobz.nxscomkr.jypbdxnt.utagwpym.wprtdznb.swldgrhm.yrbjpktq.wukovicq;

Unreachable code

if(0 != 0) {</li>
            String v1 = "flnwznvh";</li>
            if(v1.length() != 661 && v1.charAt(0) == 104) {</li>
                v1.length();</li>
            }

String Encryption

vcgrnfjx.execSQL(nvhdzjfo.xipswfqb(new String[]{"f741f04a4991fc2f0a0029f610bbd1c250dfe115fb7770b892f75d8718b822d273251013991b4407e224fa3f9d4e92f6","378f40211b6e32a5406cd97e85bcf9ad","6378a459b1c20edf", "gexnfwok", "meazfhdp", "bsmotaxn"})

It is unlikely that the programmer is crazy enough to initially develop the code. Most likely, he used one of the public obfuscators. This step is quite usual for complicating the analysis of the code in order to protect intellectual property, for example, but what kind of “outlook” it is for the researcher.

Let's pay attention to the basic encryption function:

The encryption function itself accepts 3 lines as input (if more, the rest do not make sense):

ciphertext
key
initialization vector for CBC - AES

This function is referred to in the program at least 213 times:

I note that it is an important key for normal code analysis. Next ~~you need to think~~ we have the following ways to analyze the program:

Restore the logic of the function, collect all calls in a static analysis, decrypt strings. It may be difficult and long, but it will give a 100% result.
Make changes to the application smali code, re-compile, run the application and catch the decrypted lines in the logs. It is done easily, but how the application behaves in a particular launch is unknown, and you can not see the whole picture (do not get calls for all functions). In addition, there may be problems with self-checking certificate and (or) integrity.
If it is difficult to restore the logic of the function, you can collect all the function calls and pull these functions themselves with the necessary parameters directly in the dynamics (using, for example, Frida software) .

We will choose the method number 1 as the most ~~severe~~ reliable.

Deobfuscation

Immediately make a reservation, deobfuscation is often a long and tedious process, so you need to properly evaluate your time frame. For our analysis, it is enough to decipher all the lines in at least some way and do it in the minimum time, even if in a crutch way, to mess around for a vague ideal option.

High-quality de-obfuscation makes sense in the case of a complete reverse engineering, for example, this has to be done to intellectual property thieves when they try to copy a competitor's solution, or if you often have to analyze programs processed by one obfuscator, but this is not our case.

Source code after the JEB Decompiler v.1.4 decompiler

Spoiler

publicstatic String podxiwkt(String[] args){
        int v6;
        int v4;
        byte[] v2;
        Cipher v1;
        String v10 = args[0];
        String v7 = args[1];
        String v0 = args[2];
        if(v10 == null) {
            goto label_9;
        }
        if(v10.length() != 0) {
            goto label_11;
        }
        goto label_9;
    label_11:
        IvParameterSpec v5 = new IvParameterSpec(v0.getBytes());
        try {
            v1 = Cipher.getInstance("AES/CBC/NoPadding");
            goto label_15;
        }
        catch(NoSuchPaddingException v3) {
        }
        catch(NoSuchAlgorithmException v3_1) {
        }
        String v11 = "";
        goto label_10;
    label_15:
        SecretKeySpec v9 = new SecretKeySpec(v7.getBytes(), "AES");
        int v11_1 = 2;
        try {
            v1.init(v11_1, ((Key)v9), ((AlgorithmParameterSpec)v5));
            v2 = Base64.decode(v1.doFinal(bwdoclkr.xkvasepi(v10)), 0);
            if(v2.length <= 0) {
                goto label_48;
            }
            v4 = 0;
            v6 = v2.length - 1;
        label_29:
            if(v6 < 0) {
                goto label_38;
            }
            if(v2[v6] != 0) {
                goto label_33;
            }
        }
        catch(Exception v3_2) {
            goto label_51;
        }
        ++v4;
    label_33:
        --v6;
        goto label_29;
    label_38:
        if(v4 <= 0) {
            goto label_48;
        }
        try {
            byte[] v8 = newbyte[v2.length - v4];
            System.arraycopy(v2, 0, v8, 0, v2.length - v4);
            v2 = v8;
        }
        catch(Exception v3_2) {
        label_51:
            v11 = "";
            goto label_10;
        }
    label_48:
        v11 = new String(v2);
        goto label_10;
    label_9:
        v11 = "";
    label_10:
        return v11;
    }
}

Note about decompilers

Кстати, dex2jar часто даёт сбои. Так, на рисунке ниже видно, что dex2jar версии 2.0 не смог справиться и просто выдал smali-код.

Его свежая версия, собранная из исходников, выдала декомпилированный код данной функции, но не смогла декомпилировать многие другие (вот так фокусы).

Итог: внимательно отнеситесь к выбору декомпилятора — это сэкономит вам кучу времени и будет проще, чем анализ smali-кода.

So, if we now just insert this code into the IDE, then it will not work due to errors.

It is important to remember: The decompiler is not required to issue a valid code written by the developer. He is just a magic wand when analyzing and makes assumptions how the code could be written. In most cases, after optimization by the compiler, the task of restoring the original code ceases to be trivial at all.

An example of a bad decompile:

if(v10 == null) {
            goto label_9;
        }
        if(v10.length() != 0) {
            goto label_11;
        }
        goto label_9;
…
label_9:
        v11 = "";
        return v11;

We see that it turned out bad and inoperable. Rewrite:

if ((v10 == null) || (v10.length() == 0)) {
    return"";
}

Now it has become much clearer, here is the usual input data validation. In this case, we need:

Replace all “goto” with other language constructs, since “Goto” has long been an invalid operator.
Replace calls to Android libraries with calls to Java libraries (if we are trying to execute code in the Java IDE).
Insert dependent classes referenced by our code.
Think for yourself what is wrong.

As a result, we obtain:

package com.company;
    //package isqpwcmx.isfdztgb.adscjobz.nxscomkr.jypbdxnt.utagwpym.wprtdznb.swldgrhm.yrbjpktq;import java.util.Base64;
    //import android.util.Base64;//import bnxvhlyg.nkhoirul.zfxogwqi.mdpqejcw.srnepbly.pcbvwxrs.vixdqclm.wnuqvrhp.bnvceayd.bwdoclkr;//вставим свой классimport java.security.Key;
import java.security.NoSuchAlgorithmException;
import java.security.spec.AlgorithmParameterSpec;
import javax.crypto.Cipher;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
publicabstractclassMain{
    publicMain(){
        super();
    }
    //hex to asciipublicstaticbyte[] xkvasepi(String str) {
        byte[] v0 = null;
        if(str != null && str.length() >= 2) {
            int v2 = str.length() / 2;
            v0 = newbyte[v2];
            int v1;
            for(v1 = 0; v1 < v2; ++v1) {
                v0[v1] = ((byte)Integer.parseInt(str.substring(v1 * 2, v1 * 2 + 2), 16));
            }
        }
        return v0;
    }
    publicstatic String podxiwkt(String[] args){
        int v6;
        int v4;
        byte[] v2;
        Cipher v1;
        String v10 = args[0]; //text
        String v7 = args[1]; //key
        String v0 = args[2]; //IV//checkif ((v10 == null) || (v10.length() == 0)) {
            return"";
        }
        IvParameterSpec v5 = new IvParameterSpec(v0.getBytes());
        try {
            v1 = Cipher.getInstance("AES/CBC/NoPadding");
        }
        catch(NoSuchPaddingException v3) {
            return"";
        }
        catch(NoSuchAlgorithmException v3_1) {
            return"";
        }
        SecretKeySpec v9 = new SecretKeySpec(v7.getBytes(), "AES");
        int v11_1 = 2;
        try {
            v1.init(v11_1, ((Key)v9), ((AlgorithmParameterSpec)v5));
            //v2 = Base64.decode(v1.doFinal(bwdoclkr.xkvasepi(v10)), 0);
            v2=v1.doFinal(xkvasepi(v10));
            //checkif(v2.length <= 0) {
                returnnew String(v2);
            }
        } catch(Exception v3_2) {
            return"";
        }
        v4=0;
        for (v6=v2.length-1;v6>=0;v6--){
            if (v2[v6]==0) ++v4;
        }
        if(v4 > 0) {
            try {
                byte[] v8 = newbyte[v2.length - v4];
                System.arraycopy(v2, 0, v8, 0, v2.length - v4);
                v2 = v8;
            } catch (Exception v3_2) {
                return"";
            }
        }
        v2 = Base64.getDecoder().decode(v2);
        returnnew String(v2);
    }
    publicstaticvoidmain(String[] args){
        // write your code here
        System.out.println(podxiwkt(new String[] { "b1acd584a6eae4ca6321b1f7cdf9ba9617112b4fb39e76c8def876346e3032fbd32b2d188a09715f27124c1bf9facfdc", "637904cd08aeb2d3f6a21b5c7e84f519", "8f4c796d5a3120eb", "zcmwgvdn", "mkngbsyr", "rwcdaieu" }));
    }
}

This code successfully fulfills. Once his work becomes clear, it can be simplified and simplified, leading to the originally intended laconic look written by the programmer (if, of course, his hands were not crooked initially).

Note

Кстати, в данном случае дешифрование строк можно продемонстрировать с помощью связки онлайн-ресурсов. Пример вызова шифрованной строки внутри программы:

Здесь вектор инициализации нужно сначала перевести в Hex-формат:

Подставляем все значения:

И в конце декодируем из base64:

В результате получаем обычную строку, и вызов приобретает осмысленный вид.

Thus, you need to go through the whole code and collect all the encrypted strings, now we can independently decrypt them. The important point here is that at the stage of “modifying and commenting on code” we can work both at the smali level and at the Java level (decompiled smali).

	Pluses modifications	Downsides modification
Smali	You can make changes, reassemble in dex and decompile with new lines.	It is not always easy to work on smali-code. If the change is incorrect, the application will not be collected.
Java	More often, it is much easier to extract data from high-level operations.	Edit in most Java-code viewers can not.

Another string example

vcgrnfjx.execSQL(nvhdzjfo.xipswfqb(new String[]{"f741f04a4991fc2f0a0029f610bbd1c250dfe115fb7770b892f75d8718b822d273251013991b4407e224fa3f9d4e92f6","378f40211b6e32a5406cd97e85bcf9ad","6378a459b1c20edf", "gexnfwok", "meazfhdp", "bsmotaxn"})

From here it is very easy to pick up parameters using a regular expression than to write a regular code for the following code:

Smali code, example 1

00000280  new-instance            v13, Ljava/lang/StringBuilder;
00000284  invoke-direct           {v13}, Ljava/lang/StringBuilder;-><init>()V
0000028A  const/4                 v14, 0x6
0000028C  new-array               v14, v14, [Ljava/lang/String;
00000290  const/4                 v15, 0x0
00000292  const-string            v16, "f741f04a4991fc2f0a0029f610bbd1c250dfe115fb7770b892f75d8718b822d273251013991b4407e224fa3f9d4e92f6"
00000296  aput-object             v16, v14, v15
0000029A  const/4                 v15, 0x1
0000029C  const-string            v16, "378f40211b6e32a5406cd97e85bcf9ad"
000002A0  aput-object             v16, v14, v15
000002A4  const/4                 v15, 0x2
000002A6  const-string            v16, "6378a459b1c20edf"
000002AA  aput-object             v16, v14, v15
000002AE  const/4                 v15, 0x3
000002B0  const-string            v16, "gexnfwok"
000002B4  aput-object             v16, v14, v15
000002B8  const/4                 v15, 0x4
000002BA  const-string            v16, "meazfhdp"
000002BE  aput-object             v16, v14, v15
000002C2  const/4                 v15, 0x5
000002C4  const-string            v16, "bsmotaxn"
000002C8  aput-object             v16, v14, v15

Smali code example 2

0000008E  new-array               v0, v0, [Ljava/lang/String;
00000092  move-object/from16      v89, v0
00000096  const/16                v90, 0x0
0000009A  const-string            v91, "4500b5e2e2ad26b7545eb54d70ab360ae28c9d031e2afcc3f6a2b2ac488ea440"
0000009E  aput-object             v91, v89, v90
000000A2  const/16                v90, 0x1
000000A6  const-string            v91, "da96f678922d4b07350b3a184ecc1f5e"
000000AA  aput-object             v91, v89, v90
000000AE  const/16                v90, 0x2
000000B2  const-string            v91, "0cf69e3d2745a1b8"
000000B6  aput-object             v91, v89, v90
000000BA  const/16                v90, 0x3
000000BE  const-string            v91, "jhiqsaoe"
000000C2  aput-object             v91, v89, v90
000000C6  const/16                v90, 0x4
000000CA  const-string            v91, "khbqxurn"
000000CE aput-object           v91, v89, v90

Smali code example 3

00000D3E  new-array               v0, v0, [Ljava/lang/String;
00000D42  move-object/16          v298, v0
00000D48  const/4                 v0, 0x0
00000D4A  move/16                 v299, v0
00000D50  const-string            v0, "b286945744e085f4d5c19916fd261481"
00000D54  move-object/16          v300, v0
00000D5A  move-object/from16      v0, v300
00000D5E  move-object/from16      v1, v298
00000D62  move/from16             v2, v299
00000D66  aput-object             v0, v1, v2
00000D6A  const/4                 v0, 0x1
00000D6C  move/16                 v299, v0
00000D72  const-string            v0, "df6883742b2911ac5ac7b4dee065390f"
00000D76  move-object/16          v300, v0
00000D7C  move-object/from16      v0, v300
00000D80  move-object/from16      v1, v298
00000D84  move/from16             v2, v299
00000D88  aput-object             v0, v1, v2
00000D8C  const/4                 v0, 0x2
00000D8E  move/16                 v299, v0
00000D94  const-string            v0, "90a463ce2df17b58"
00000D98  move-object/16          v300, v0
00000D9E  move-object/from16      v0, v300
00000DA2  move-object/from16      v1, v298
00000DA6  move/from16             v2, v299
00000DAA  aput-object             v0, v1, v2
00000DAE  const/4                 v0, 0x3
00000DB0  move/16                 v299, v0
00000DB6  const-string            v0, "cupyzsgq"
00000DBA  move-object/16          v300, v0
00000DC0  move-object/from16      v0, v300
00000DC4  move-object/from16      v1, v298
00000DC8  move/from16             v2, v299
00000DCC  aput-object             v0, v1, v2

As we see, the internal variables change, the sequence of commands differs, the number of arguments also varies, in addition to the program, the decryption function is not called directly, but through the functions of the interlayer. Try to write a rule yourself to search for this construct, not to make mistakes on capturing strings from other functions, and do it all quickly ( ~~good luck~~ ).

Plan-trap:

Extract all values from decompiled code.
We decrypt.
Let's replace the ciphertext with the one opened in smali-code. We substitute, for example, in exchange for the first operator. (It will be more professional to cut out the entire function call and leave the returned decrypted string, but then again there is a big risk to break the program).
We collect the smali-code in a dex-file.
We will continue to look further in the code analyzer, from which we started.

If you compile the entire decompiled code into one file, you will get about 20,000 lines, which for manual analysis takes a lot of time, which is clearly more expensive than the boots I have put up for sale. To begin with we will collect all strings with a regular expression.

We see 593 coincidences, plus about a dozen that did not fall under this rule, ~~in a family with a black sheep~~ . Example:

Sort, weed out, total 422 unique lines: We

skip through the decryption function that we restored earlier. Result:

Replace the ciphertext with the one opened in smali-code using Python:

import os
words_replace=dict()
words_replace["0018aacad3d146266317d8d8c51785fd"]="imei"
words_replace["016d15e4d0a72667c61428e736a6f3b8"]="WakeLock"
words_replace["032c534efb6c9990cd845a08c5a08b95"]="inbox"
#… и т.д.
#Открыть smali-файл
#Найти все вхождения массива и заменить
def change(path):
    print("file="+path)
    file_handle = open(path, 'r')
    context_full = file_handle.read()
    file_handle.close()
    for i in words_replace:
        context_full=context_full.replace(i, words_replace[i])
        #print (i+""+words_replace[i])
    file_handle = open(path, 'w')
    context_full = file_handle.write(context_full)
    file_handle.close()
#Пройтись по всем подпапкам и открыть smali-файлы
for top, dirs, files in os.walk('C:\\work\\test'):
    for nm in files:
        path=os.path.join(top, nm)
        print (path)
        change(path)

We compile smali-files in dex:

Now it can be somehow analyzed (reading the first argument from the whole construction):

Analysis

So, we have 20,000 more or less readable lines of code, we don’t have to do a complete analysis before us. It is necessary to understand the functionality as a whole. Here, in essence, only the skill of reading Java source code is required. Walk through the code, look at cross-references, rename variables and functions.

How is it better to analyze the Android application, especially large?

Option 1: You can move away from the Manifest file.

For example, from LAUNCHER you can try to unwind the entire call chain. By the way, do not forget that there is still “Receiver” and “Service”, which can change the linear execution of the program.

Full Manifest File

<?xml version="1.0" encoding="utf-8" standalone="no"?><manifestxmlns:android="http://schemas.android.com/apk/res/android"android:installLocation="internalOnly"package="xfmpuwon.mtnbupnc.ihqdgjal.ndgmqawx.bjunzerq.cznfpnoq.fzevcuym.jmpdiqft"><uses-permissionandroid:name="xfmpuwon.mtnbupnc.ihqdgjal.ndgmqawx.bjunzerq.cznfpnoq.fzevcuym.jmpdiqft.permission.C2D_MESSAGE"/><uses-permissionandroid:name="com.google.android.c2dm.permission.RECEIVE"/><uses-permissionandroid:name="android.permission.SEND_SMS"/><uses-permissionandroid:name="android.permission.INTERNET"/><uses-permissionandroid:name="android.permission.READ_PHONE_STATE"/><uses-permissionandroid:name="android.permission.ACCESS_NETWORK_STATE"/><uses-permissionandroid:name="android.permission.WAKE_LOCK"/><uses-permissionandroid:name="android.permission.SYSTEM_ALERT_WINDOW"/><uses-permissionandroid:name="android.permission.MODIFY_AUDIO_SETTINGS"/><uses-permissionandroid:name="android.permission.CHANGE_NETWORK_STATE"/><uses-permissionandroid:name="android.permission.RECEIVE_SMS"/><uses-permissionandroid:name="android.permission.RECEIVE_BOOT_COMPLETED"/><uses-permissionandroid:name="android.permission.QUICKBOOT_POWERON"/><uses-permissionandroid:name="android.permission.READ_SMS"/><uses-permissionandroid:name="android.permission.ACCESS_WIFI_STATE"/><uses-permissionandroid:name="android.permission.CHANGE_WIFI_STATE"/><permissionandroid:name="xfmpuwon.mtnbupnc.ihqdgjal.ndgmqawx.bjunzerq.cznfpnoq.fzevcuym.jmpdiqft.permission.C2D_MESSAGE"android:protectionLevel="signature"/><applicationandroid:allowBackup="true"android:icon="@drawable/icon"android:label="@string/tgiwmpqy"android:noHistory="true"><activityandroid:configChanges="orientation"android:excludeFromRecents="true"android:label="@string/tgiwmpqy"android:launchMode="singleTop"android:name="zemquyog.csrtmnak.xrkfygen.wkahrnjd.acnfunjh.rgipxbuf.lruiwxeg.blqndche.dcjihbou"android:screenOrientation="portrait"><intent-filter><actionandroid:name="android.intent.action.MAIN"/><categoryandroid:name="android.intent.category.LAUNCHER"/></intent-filter></activity><activityandroid:configChanges="orientation"android:launchMode="singleTop"android:name="xbfrscou.hxrvwnoi.djvpcqri.enlnrfio.aoegxbiu.heywzmnb.znfnxcht.nazcxobq"android:screenOrientation="portrait"/><activityandroid:configChanges="orientation"android:launchMode="singleTop"android:name="hcfkagds.timkagsd.oetvghzr.fcioynvl.psynofdj.slcghdjz.tapnwsdk.gzvwnban.htenafdb.qwebhzgy"android:noHistory="true"android:screenOrientation="portrait"/><activityandroid:configChanges="orientation"android:excludeFromRecents="true"android:launchMode="singleTop"android:name="njfbwmre.voefarqx.ftuxvngl.wrmshxqj.zdenywgn.eiwyunlg.jysgkbam.yrijthab.vstqxpuo.iplamgxf"android:priority="2147483647"android:screenOrientation="portrait"/><receiverandroid:name="gfbaznoc.asyoqtnm.kbetoqca.mqysobzu.gqwfibrv.dorxijuk.wgzkmiep.ywnnurzv.csfpqhrn"android:permission="android.permission.BIND_DEVICE_ADMIN"><meta-dataandroid:name="@string/pkzrlscm"android:resource="@xml/ynqukvnb"/><intent-filterandroid:priority="2147483646"><actionandroid:name="android.app.action.DEVICE_ADMIN_ENABLED"/></intent-filter></receiver><receiverandroid:name="ykwbodxc.gymjhibn.kgmdfqor.hbasvmfz.yegkmaif.ortzknvm.quplincn.cuxytvhs.fqonzuts.cyuoxgqi.znumwyct"android:permission="com.google.android.c2dm.permission.SEND"><intent-filter><actionandroid:name="com.google.android.c2dm.intent.RECEIVE"/><actionandroid:name="com.google.android.c2dm.intent.REGISTRATION"/><actionandroid:name="com.google.android.c2dm.intent.UNREGISTRATION"/><categoryandroid:name="xfmpuwon.mtnbupnc.ihqdgjal.ndgmqawx.bjunzerq.cznfpnoq.fzevcuym.jmpdiqft"/></intent-filter></receiver><receiverandroid:enabled="true"android:exported="true"android:name="kqwihjot.nvkqjloc.grjnyknm.owydvckh.mugknwdx.enhcyvja.mhvbpcue.ztbwjhfo"><intent-filterandroid:priority="2147483646"><actionandroid:name="android.intent.action.LOCKED_BOOT_COMPLETED"/><actionandroid:name="com.htc.intent.action.QUICKBOOT_POWERON"/><actionandroid:name="android.intent.action.QUICKBOOT_POWERON"/><actionandroid:name="android.intent.action.BOOT_COMPLETED"/><actionandroid:name="android.intent.action.USER_PRESENT"/><actionandroid:name="android.intent.action.BATTERY_OKAY"/><actionandroid:name="android.intent.action.BATTERY_LOW"/><actionandroid:name="android.intent.action.ACTION_POWER_CONNECTED"/><actionandroid:name="android.intent.action.ACTION_POWER_DISCONNECTED"/><actionandroid:name="android.intent.action.APP_ERROR"/><actionandroid:name="android.intent.action.HEADSET_PLUG"/><actionandroid:name="android.intent.action.PHONE_STATE"/><actionandroid:name="android.intent.action.NEW_OUTGOING_CALL"/><actionandroid:name="android.provider.Telephony.SMS_RECEIVED"/><actionandroid:name="android.intent.action.TIME_TICK"/><actionandroid:name="android.intent.action.SCREEN_ON"/><actionandroid:name="android.intent.action.SCREEN_OFF"/><actionandroid:name="android.net.conn.CONNECTIVITY_CHANGE"/><actionandroid:name="android.net.wifi.WIFI_STATE_CHANGED"/><actionandroid:name="android.intent.action.DREAMING_STOPPED"/><categoryandroid:name="android.intent.category.HOME"/></intent-filter></receiver><receiverandroid:name="btnsxnuz.wmjizbky.lynvjxqz.zinomjuv.yizlgcnf.qwoikgnc.wnrskjea.wfqgmeny.lcgvqrms.ocwkgblp"><intent-filterandroid:priority="2147483646"><actionandroid:name="android.provider.Telephony.SMS_RECEIVED"/></intent-filter></receiver><serviceandroid:name="ltvsrezg.ehxndrat.twnnyxrf.nqynefws.dhbalcnr.ynjkuxod.nhoxmsbq.nackoyhn.voycgfek.znhwkqba.taxvnfyn"/><serviceandroid:name="rbnakfzo.qsreiubk.pwvlnngs.twoxnhfv.mftarcnd.pfioxcub.xjlaftqr.nxrqvlwh"/><serviceandroid:enabled="true"android:name="xfmpuwon.mtnbupnc.ihqdgjal.ndgmqawx.bjunzerq.cznfpnoq.fzevcuym.jmpdiqft.ugshpjvo"/></application></manifest>

Option 2: You can move from interesting lines

Part of the decrypted lines

system_update.apk
(Общее)
(Перехват)
, error = 
, unregistered = 
, в 
.permission.C2D_MESSAGE
//sky-sync.pw/
//sms/inbox
/system_update.apk
ALLCONTACTS
ALLMSG
AUTHENTICATION_FAILED
Acquiring wakelock
Application
BLOCKER_BANKING_START
BLOCKER_EXTORTIONIST_START
BLOCKER_STOP
BLOCKER_UPDATE_START
Banking
CHANGE_GCM_ID
CONTACTS
CONTACTS_PRO
CREATE TABLE IF NOT EXISTS 
END
Error|No process list|No access
Extortionist
Foreground
GCM returned invalid number of 
GCMBaseIntentService
GCMBroadcastReceiver
GCMIntentService-
GCMRegistrar
GCM_LIB
GET
MESSAGE
Mobile Network
NEWMSG
Not retrying failed operation
ONLINE
PAGE
POST
Process finished with exit code 0
RESTART
Received deleted messages 
Registering receiver
Releasing wakelock
SERVICE_NOT_AVAILABLE
SSL
START
STOP
Saving regId on app version 
Scheduling registration retry, backoff = 
Setting registeredOnServer status as 
Stop
System
UNBLOCK
UPDATE
UPDATE_PATTERNS
URL
UTF-8
Update
WakeLock
Wakelock reference is null
Wi-Fi
WiMax
_success
add_msg_ok
address
android.intent.action.QUICKBOOT_POWERON
answer_text
answer_to
api_url
app
appVersion
application
application/vnd.android.package-archive
apps_list
ask
backoff_ms
blocker
blocker_banking
blocker_banking_autolock
blocker_banking_forced_access
blocker_banking_success
blocker_extortionist
blocker_extortionist_autolock
blocker_extortionist_forced_access
blocker_extortionist_success
blocker_update
blocker_update_forced_access
blocker_update_success
body
build
callback
cardSuccess
check
com.android.settings
com.google.android.c2dm.intent.RECEIVE
com.google.android.c2dm.intent.REGISTER
com.google.android.c2dm.intent.REGISTRATION
com.google.android.c2dm.intent.UNREGISTER
com.google.android.gcm
com.google.android.gcm.intent.RETRY
com.google.android.gsf
com.htc.intent.action.QUICKBOOT_POWERON
command
command_receive
contactslist
country
data
date
delete
deleted_messages
device_block
disableDataConnectivity
enableDataConnectivity
error
failure
file deleted.
first_start
force-locked
gafzpjxb.cix
gcm
gcm_id
gcm_register
gcm_register_ok
getITelephony
get_message_list
id integer primary key autoincrement,
id=?
imei
immunity
inbox
init_bootable
init_imei
is_admin
is_awake_display
is_imunnity
is_locked
is_network_type
is_top_activity
job
job_date
job_id
komgejif.hqr
locked
message
message_delivered
message_type
method
model
msg
msg_id
msglist
name
not
nypjtinq.nvp
ok
onServer
onServerExpirationTime
onServerLifeSpan
operator
org.android.sys.admin.disabled
org.android.sys.admin.enabled
org.android.sys.admin.request
org.android.sys.command.receive
org.android.sys.launch.first
org.android.sys.sms.pro.sent
org.android.sys.sms.push
org.android.sys.sms.sent
outbox
page
params
pattern
patterns
personal
phone
phone_list
privet
process_list
protocol
qwertyuiopasdfghjklzxcvbnm
receive
regId
regex
register
register_ok
registrationId = 
registration_id
repeat
resetting backoff for 
ru
save_contacts_list
save_message_history
sender
sent
sent_status
sid
ss
status
stop_blocker
text
text,
text/html
time
token
total_deleted
type
unknown
unregistered
until 
url
useragent
utf-8
value
version
xpls
yes
Идет инициализация приложения!
Не удалось установить приложение
Подождите...
Приложение вылетело в 
Приложение лишилось прав администратора в 
Приложение получило права администратора в 
Приложение проверено и является полностью безопасным! Выполнить запуск?
Приложение пытаются лишить прав администратора в 
Устройство перезапущено в 
отказ безопасности в 
перезапускаем его
является системным!

Option 3: You can move from interesting resources (assets, libs)

In this case, option 3 turned out to be preferable. In the folder / assets (apk-container) are three interesting html-files. Here is their view in the browser:

It looks doubtful for the official Avito payment transfer program, don't you think so? Track what happens when you press the key to send bank data on a page with the Sberbank logo. JavaScript calls the function sendCardData():

And then it is transmitted to the Java code through a call ok.performClick():

In the Java code, the processing is performed:

Further, all this is encrypted in the class mcrypt:

Inside the function, data is encrypted as previously discussed:

But for everything else, the keys are hard-wired:

We try to decrypt through an online-resource:

And convert from base64. Success! We can decrypt all application data: checked on traffic captured earlier.

The application reports all events to the server.

{
	"sid":15,
	"imei":"861117030537111",
	"phone":"System",
	"message":"Приложение получило права администратора в 22.10.2018 23:30:47",
	"time":"1540240247",
	"msg_id":1,
	"status":"unknown",
	"type":"inbox",
	"method":"message"
}

And also periodically transfers all running applications.

{
	"sid": 15,
	"imei": "861117030537111",
	"country": "ru",
	"operator": "MTS RUS",
	"phone": "",
	"model": "Xiaomi Redmi 3X",
	"version": "6.0.1",
	"application": "ПРК",
	"build": "30.0.2",
	"process_list": [
		"Background|com.android.bluetooth|com.android.bluetooth.hid.HidService",
		"Background|com.android.settings:remote|com.android.settings.wifi.MiuiWifiService",
		"Background|com.android.phone|org.codeaurora.ims.ImsService",
		"Background|system|com.qualcomm.location.LocationService",
		...,
		"Background|xfmpuwon.mtnbupnc.ihqdgjal.ndgmqawx.bjunzerq.cznfpnoq.fzevcuym.jmpdiqft|ltvsrezg.ehxndrat.twnnyxrf.nqynefws.dhbalcnr.ynjkuxod.nhoxmsbq.nackoyhn.voycgfek.znhwkqba.taxvnfyn"
	],
	"apps_list": [
		"com.introspy.config",
		"com.google.android.youtube",
		"com.google.android.googlequicksearchbox",
		"org.telegram.messenger",
		...,
		"com.google.android.inputmethod.latin",
		"jakhar.aseem.diva"
	],
	"method": "register"
}

If I had a window for entering bank data in dynamics, then the data would have been in traffic. Thus, we can conclude that this is a “phishing” application.

Those who were attentive noticed that there are quite a few permissions in the Manifest file, and the application has more rich functionality. We will carry out a deep analysis of the functional in another article. In the meantime, success!

findings

I am disappointed that I did not sell the boots. And the conclusions are:

~~Do not sell boots on Avito~~
Do not follow obscure links (even if from friends and even if “you need to urgently borrow 100 rubles - a matter of life and death”)
Do not download applications, except from Google Play or AppStore
- Disable the installation from "unreliable sources", if you really do not understand what's what.
- Do not disable Play Protect.
- Remember, there may be malware on Google Play
Install antivirus on the phone (really works).
If you are a developer, don't obfuscate the code, let people see your good intentions (joke)
If you are a researcher, do not work on food and analyze applications in your free time and publish reports. Together we will make the world a better place.

PS I tried to write an article in a slightly humorous format and submit as simply as possible, because even I wouldn’t want to read a serious longrid called “Reverse engineering of an obfuscated malicious application on the Android OS” on Friday.

Tags:

How I almost caught a virus trying to sell my boots

A pleasant surprise

Altruism

Dive into the abyss

Tools

Only old men go to battle

Overview

Deobfuscation

Analysis

findings

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