Analysis of a Trojan in JAVA

Igual eu te falei aquele dia e voce nao quis acreditar. Friend to people counts not finger!
Veja só o que seu amiguinho andou aprontando nessas fotos.
DSC02421.jpg (568.3 KB)
DSC02521.jpg (603.4 KB)

That link leads to an executable file: http://www.givin[DELETED].com/UserFiles/File/photos.php?0.19325211365355321.

When you download the Trojan and observe it with Peid you will find that it is packaged with UPX. If we open the EXE we will see a string like this:

.rdata:00414BA8 0000000B C WINRAR. SFX
.rdata:00414BCC 00000039 C d:\\Projects\\WinRAR\\SFX\\build\\sfxrar32\\Release\\sfxrar.pdb

Now let's go to the best, decompile the . CLASS, the compiled JAVA files (the famous . OBJ). These files are interpreted by the JAVA classloader and are executed as one more application. There are many JAVA CLASS file decompilers and one of the best known is the JAVA Decompiler DJ.

We will see the Imports, some interesting and others not so much.

import b.d;
import by.squareroot.injector.lib.MyKernel32;
import by.squareroot.injector.struct.Context;
import by.squareroot.injector.struct.MemoryBasicInformation;
import by.squareroot.injector.struct.ProcessInformation;
import by.squareroot.injector.struct.StartupInfoA;
import by.squareroot.injector.struct.TotalProcInfo;
import by.squareroot.injector.struct.WoW64Context;
import by.squareroot.injector.struct.pe.MZHeader;
import by.squareroot.injector.struct.pe.PEInfo;
import by.squareroot.injector.struct.pe.PE_ExtHeader;
import by.squareroot.injector.struct.pe.PE_Header;
import by.squareroot.injector.struct.pe.SectionHeader;
import com.sun.jna.Platform;
import com.sun.jna.Pointer;
import com.sun.jna.platform.win32.Advapi32Util;
import com.sun.jna.platform.win32.WinReg;
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.nio.ByteBuffer;
import java.util.Properties;

We must not give up there (we must learn to look as the great Fravia, QEPD taught us) we will look a little further we will find a reference in this stitio that seems to be from another reverser analyzing jaZEUS.

If we read that article a little and then continue with it we can conclude two things:

1. The creator of this virus used the same technique and resources as the jaZEUS virus to infect its victims.
2. It is a variant of JAZeus or the original version.

In JAZeus apparently the two .EXE are encrypted, in our variant, only app.exe is encrypted and dummy.exe not, we can see it simply by opening the EXE and seeing its header. If we debug dummy.exe we will see that it is another dropper made in C++ that will seek to decrypt app.exe, looking for the encryption method in the method file and then using that parameter to decrypt and execute it.

Apparently the method of unpacking this virus is the same as JAZeus does, with the variant that the launcher does not have. From what I see the launcher is unified in a.class since it runs app.exe after decrypting it from there inside. The injector package takes care of the assembly and in-memory injection of the executable for the execution of the actual virus. In the method "a" of the class "a", we will see that it is put at the beginning to start when our OS starts:

s = a("data/app.exe");
b.a a1 = a();
try
{
ifnull)
{
String s1;
if((s1 = ((Properties) (obj)).getProperty("hklmnull)
{
String s2 = a();
Advapi32Util.registrySetStringValue(WinReg.HKEY_LOCAL_MACHINE, "SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Run\\", s1, s2);
}
String s3;
if((s3 = ((Properties) (obj)).getProperty("hklunull)
{
obj = a();
Advapi32Util.registrySetStringValue(WinReg.HKEY_CURRENT_USER, "Software\\Microsoft\\Windows\\CurrentVersion\\Run\\", s3, ((String) (obj)));
}
}
}

If it becomes a JAZeus we will have some more security problems, we can also find the 3DES encryption method as a string in the others. CLASS, in addition to a possible key, phrase widely used as a demo of blog post, etc.

Spark by Disidents

See original.