Recently, the Northeast Ohio Information Security Forum put on a malware reverse engineering challenge. The winners still haven’t been announced because they’re still reviewing all the submissions but below is the write up that I submitted:
Describe your malware lab.
My lab is a simple setup. It consists of a MacBook with 2GB of memory running MacOSX 10.5.5. I use VMWare Fusion 2.0 since this lets me take multiple snapshots and revert back to any of my previous snapshots. I have two virtual machines setup. The first one is a stock Windows XP Pro machine with minimal extra software installed. OllyDbg is the main application installed along with other utilities like Process Monitor, Regshot, Wireshark and PEiD. The other virtual machine is a stock Ubuntu 8 machine used only when I need a Linux platform for analysis.
Is the malware packed? If so, how did you determine what it was?
I chose to answer this question second since if an executable is packed then there isn’t a lot of static analysis you can do until it is unpacked.
The first thing I did, was open up malware.exe in OllyDbg. OllyDbg immediately displayed the following warning:
“Quick statistical test of module ‘malware’ reports that its code section is either compressed, encrypted, or contains large amount of embedded data. Results of code analysis can be very unreliable or simply wrong. Do you want to continue analysis?”
This is usually a good first indication that an executable might be packed. The next thing I did, was to look at the different sections in the executable. Usually, in typical applications, you find sections like .text, .data or .rsrc. When I opened up the memory window in OllyDbg the following is what I saw:
Notice that the only sections that are present are ones called ABC0, ABC1 and ABC2 and the typical ones I listed above are not present. This was another good indication to me that the executable was packed. The way that packers typically work are to take an existing executable and transform it in some way and then include an unpacking stub that is executed first to reverse the previous transformation. A lot of the time what you will see is an extra section added and then the entry point of the executable changed to execute the unpacking stub first and then it jumps to the unpacked code. These ABC sections also stood out to me as being similar to what you see in a UPX packed executable. In a typical UPX packed executable you will see sections like
UPX2. So It seems like this executable is packed and possibly with some sort of modified UPX packer.
Next I looked at the function imports of the executable. So I opened up the Names window in OllyDbg.
This stands out to me as a pretty short list, with almost all of the imports from KERNEL32.dll. Normally you would find a long list of imports and from many different DLLs. Additionally the functions that are imported are things for loading additionally libraries manually (LoadLibraryA, GetProcAddress) and modifying memory (VirtualProtect, VirtualAlloc, …).
This convinced me that this is a packed executable but I wasn’t a hundred percent sure what it was packed with. My guess was UPX and to double check this I opened up malware.exe in PEiD, and this was the results:
So I was correct. The executable is packed and is packed with UPX.
What information can you gather about the malware without executing it?
Before attempting static analysis I first needed to unpack the executable. I first tried downloading the UPX utility and running the upx command to unpack the program. Since malware.exe had non standard section names the UPX utility was not able to do the job. I did a quick google search on manual unpacking of UPX and found this article, http://vault.reversers.org/UPXUnpackingTut, that told me how to do it. When the UPX unpacking stubs starts it does a
PUSHAD instruction to save all the registers, then unpacks, then does a
POPAD to restore the registers and then jumps to the original entry point of the application. All that I needed to do was to locate the
POPAD instruction and place a breakpoint on the jmp instruction. I found the following code:
0047AFBE 61 POPAD 0047AFBF 8D4424 80 LEA EAX,DWORD PTR SS:[ESP-80] 0047AFC3 6A 00 PUSH 0 0047AFC5 39C4 CMP ESP,EAX 0047AFC7 ^75 FA JNZ SHORT malware.0047AFC3 0047AFC9 83EC 80 SUB ESP,-80 0047AFCC -E9 FB59F9FF JMP malware.004109CC
I then set a breakpint at
0x0047AFCC, ran OllyDbg to that line, and then used OllyDump to save the
unpacked executable to my hard drive.
Now that the executable was unpacked I started the static analysis. The first thing I did was to run the
strings command on the unpacked file. This alone revealed a lot about the malware. The following is a list of strings that caught my attention:
There were a lot of
Echostrings that were creating a
1.regfile. So at some point I would guess that registry modifications are made
I started to see a lot of strings with
RealmBoTin it. A quick google search turned up a handful of pages offering to let me download groups of bot source code, one of them being Crx- realmbot.VNC+RFI.
I also noticed a list of web page names like PayPal, Gmail, Yahoo!, so possible the malware is looking for these pages
Next I saw a long list of what seemed like random words. My guess would be that this is a password list of some sort for trying to brute force passwords for something.
Then I started noticing some strings about IRC. Things like NICK, USER, PASS, for example. I would guess that this malware tries to connect to an irc server. Earlier there were some strings of #chalenge so maybe that is the channel that the bot tries to connect to
I noticed some strings about remote shell, so I would guess the program provides some way to spawn a remote shell
Some of the strings suggested that the program could start a ftp server
I found the string,
Normal key logger active. This indicates to me that there is some sort of key logging functionality that can be activated.
There were also some strings about DDoS flooding
There were a handful of strings that seemed to deal with downloading files.
There were many strings throughout the program that suggested that there was some sort of httpd functionality.
All of these things are just what I gathered from reading the output from the
strings command. At first guess I would think based on the name RealmBoT throughout the binary and all the different sort of commands found that this is some sort of IRC bot that installs itself on the victim machine, connects to an irc server and then waits for commands.
Next I started to analyze the main function of the program in OllyDbg to try to figure out what it does on start up. The first function, called from the main function that I noticed was at
0x00401CEE, here’s a snippet from the start of it:
00401CEE > 53 PUSH EBX 00401CEF 55 PUSH EBP 00401CF0 8B2D A0804100 MOV EBP,DWORD PTR DS:[<&kernel32.GetModuleHandleA>] 00401CF6 56 PUSH ESI 00401CF7 57 PUSH EDI 00401CF8 68 B4C44100 PUSH malware-.0041C4B4 ; ASCII "kernel32.dll" 00401CFD FFD5 CALL EBP ; GetModuleHandle 00401CFF 8B35 B0804100 MOV ESI,DWORD PTR DS:[<&kernel32.GetProcAddress>] 00401D05 8BF8 MOV EDI,EAX ; EDI = Kernel32Handle 00401D07 33DB XOR EBX,EBX 00401D09 3BFB CMP EDI,EBX ; Make sure we got a handle to kernel32 00401D0B 0F84 FD000000 JE malware-.00401E0E 00401D11 68 A4C44100 PUSH malware-.0041C4A4 ; ASCII "SetErrorMode" 00401D16 57 PUSH EDI 00401D17 FFD6 CALL ESI 00401D19 68 88C44100 PUSH malware-.0041C488 ; ASCII "CreateToolhelp32Snapshot" 00401D1E 57 PUSH EDI 00401D1F A3 C8B64200 MOV DWORD PTR DS:[<lpSetErrorMode>],EAX
This function continued on like this for a long time. Basically the author of this malware is loading almost of all the libraries they needed dynamically. This can make the disassembly less obvious because OllyDbg can’t always figure out what the function pointer being called really is. I went through this function and labeled the imports so that the rest of the disassembly would make more sense.
Back in the main function, after the load library function is called, the program calls CreateMutex and
WaitForSingleObject so that it makes sure only one instance of itself is running at the same time. After that it initializes the winsock library for network functionality.
004038D0 BF 04010000 MOV EDI,104 004038D5 8D85 18FCFFFF LEA EAX,DWORD PTR SS:[EBP-3E8] 004038DB 57 PUSH EDI 004038DC 50 PUSH EAX 004038DD FF15 5C804100 CALL DWORD PTR DS:[<&kernel32.GetWindowsDirectoryA>] 004038E3 8D85 1CFDFFFF LEA EAX,DWORD PTR SS:[EBP-2E4] 004038E9 57 PUSH EDI 004038EA 50 PUSH EAX 004038EB 56 PUSH ESI 004038EC FF15 A0804100 CALL DWORD PTR DS:[<&kernel32.GetModuleHandleA>] 004038F2 50 PUSH EAX 004038F3 FF15 9C804100 CALL DWORD PTR DS:[<&kernel32.GetModuleFileNameA>]
This code above is the start of the program trying to figure out if this is the first time it has run or not. It does this by calling
GetModuleFileNameA and looking to see if the fully-qualified path returned from
GetModuleFileNameA contains the windows directory. If it does not contain the windows directory then it considers this the first run. If this is the first run then it will make a copy of itself in the windows directory as a file named
Winsec32.exe. Then the code will call
CreateProcessA to start the copy running and then
ExitProcess to stop the first copy from running.
Winsec32.exe instance starts up it will go through the same check again to determine if the running process is running in the Windows directory. This time however the code will determine that this is not the first time the program has run and continue running at
The next function that is called is at
0x00408E8A. This function calls 4 other functions:
RegCloseKey. This function takes a single argument passed in from the main function. The main function calls it passing in the
Winsec32.exe string. The functions purpose it to call
RegSetValueExA on a list of key and sub key values if the argument is not NULL. If the argument is NULL, then the function will call
RegDeleteValueA and remove all of the values that might have been previously set. The following is the list of keys/sub keys at
0x0041E5F4 that get set:
For each of these keys
RegSetValueExA is called setting
lpValueName equal to
Microsoft Svchost local services and the
Next comes some strings that I would assume are related to IRC based on the first one.
00403B5B 6A 7F PUSH 7F 00403B5D 68 00C84100 PUSH malware-.0041C800 ; ASCII "testirc1.sh1xy2bg.NET" 00403B62 68 4C554700 PUSH malware-.0047554C 00403B67 E8 D4B90000 CALL malware-.0040F540 00403B6C A1 B8C74100 MOV EAX,DWORD PTR DS:[41C7B8] 00403B71 6A 3F PUSH 3F 00403B73 68 18C84100 PUSH malware-.0041C818 ; ASCII "#chalenge" 00403B78 68 CC554700 PUSH malware-.004755CC 00403B7D A3 9C564700 MOV DWORD PTR DS:[47569C],EAX 00403B82 E8 B9B90000 CALL malware-.0040F540 00403B87 83C4 40 ADD ESP,40 00403B8A 6A 3F PUSH 3F 00403B8C 68 24C84100 PUSH malware-.0041C824 ; ASCII "happy12" 00403B91 68 0C564700 PUSH malware-.0047560C 00403B96 E8 A5B90000 CALL malware-.0040F540
It looks like the function at
0x0040F540 is some sort of string copy and these strings deal with IRC.
testirc1.sh1xy2bg.NET looks like a host name, so probably the IRC server to connect to.
#chalenge is a channel and I would guess that
happy12 is either a user name or a password.
After this comes the final part of the main function that looks to be a run loop
00403B9B 83C4 0C ADD ESP,0C 00403B9E 8935 A0564700 MOV DWORD PTR DS:[4756A0],ESI 00403BA4 33FF XOR EDI,EDI 00403BA6 3935 00B74200 CMP DWORD PTR DS:[42B700],ESI 00403BAC 75 16 JNZ SHORT malware-.00403BC4 00403BAE 8D45 F8 LEA EAX,DWORD PTR SS:[EBP-8] 00403BB1 56 PUSH ESI 00403BB2 50 PUSH EAX 00403BB3 FF15 20B54200 CALL DWORD PTR DS:[<lpInternetGetConnectedState>] 00403BB9 85C0 TEST EAX,EAX 00403BBB 75 07 JNZ SHORT malware-.00403BC4 00403BBD 68 30750000 PUSH 7530 00403BC2 EB 26 JMP SHORT malware-.00403BEA 00403BC4 68 48554700 PUSH malware-.00475548 00403BC9 8935 A85D4700 MOV DWORD PTR DS:[475DA8],ESI 00403BCF E8 3C000000 CALL malware-.00403C10 00403BD4 83F8 02 CMP EAX,2 00403BD7 8945 FC MOV DWORD PTR SS:[EBP-4],EAX 00403BDA 74 20 JE SHORT malware-.00403BFC 00403BDC 3935 A85D4700 CMP DWORD PTR DS:[475DA8],ESI 00403BE2 74 01 JE SHORT malware-.00403BE5 00403BE4 4F DEC EDI 00403BE5 68 B80B0000 PUSH 0BB8 00403BEA FF15 4C804100 CALL DWORD PTR DS:[<&kernel32.Sleep>] 00403BF0 47 INC EDI 00403BF1 83FF 06 CMP EDI,6 00403BF4 ^7C B0 JL SHORT malware-.00403BA6 00403BF6 837D FC 02 CMP DWORD PTR SS:[EBP-4],2 00403BFA ^75 A8 JNZ SHORT malware-.00403BA4 00403BFC E8 7EFAFFFF CALL malware-.0040367F 00403C01 FF15 38B54200 CALL DWORD PTR DS:[<lpWSACleanup>] 00403C07 5F POP EDI 00403C08 5E POP ESI 00403C09 33C0 XOR EAX,EAX 00403C0B 5B POP EBX 00403C0C C9 LEAVE 00403C0D C2 1000 RETN 10
What we see here is at
EDI register is initialized to 0. Instructions are executed and then at
0x00403BF0 we increment the
EDI register and check to see if it is 6. If it is not 6 then we jump back to the beginning of the loop. If it is 6 then we check another variable to see if it is equal to 2 and if it’s not then we loop back to zeroing out the EDI register. Essentially the code in here will run until the variable at [EBP-4] is equal 2. When it is equal to 2 then we call the function at
0x0040367F and then
WSACleanup. Inside of the loop the first function call is a call to
InternetGetConnectedState. If this machine is not connected to the internet, then we end up at the call to
kernel32.Sleep and then we loop. If it is connected to the internet then the next function to be called is at
0x00403C10. Just glancing inside the function at
0x00403C10 I see calls to things like
closesocket. My guess base on the fact that the code right before the main loop appeared to be setting a host name and channel is that the function at
0x00403C10 is what tries to do the IRC connection.
Describe the malware’s behavior. What files does it drop? What registry keys does it create and/or modify? What network connections does it create? How does it auto-start, etc?
Based on the malware’s disassembly the behavior seems to be as follows: Create a copy of the malware in the Windows directory named Winsec32.exe, create three registry keys to get the malware to start at system startup, and then try to connect to an IRC server. To verify these findings I set out to actually run and observer the malware. I started by taking a snapshot of my virtual machine so that I could revert back to a clean state after running the malware. I then started up some utilities to help me observe the actions of the malware. I started regshot and took an initial snapshot of the registry. I also started
Process Monitor so I could watch what files were being written to. I then started up a network sniffer to see what the malware tried to connect to. Unfortunately the VMWare Fusion network driver on MacOSX doesn’t have BPF support so I couldn’t use Wireshark directly. Instead I started up the
vmnet-sniffer utility that comes with VMWare Fusion which will log virtual machine network traffic in a raw format that can be opened in Wireshark at a later time.
I then started malware.exe and watched what happened in
Process Monitor. In the screenshot below, I’ve highlighted all the
WriteFile calls and the
This confirms what I found while following the disassembly of the main function. When the malware starts up it will make a copy of itself in the Windows directory called Winsec32.exe and then start Winsec32.exe running and terminate. Now that it seemed like the malware had “installed” itself, I took a second snapshot of the registry with regshot and then compared it to the original. The results below also confirm what I found during static analysis.
Regshot 1.8.2 Comments: Datetime:2008/10/18 11:30:28 , 2008/10/18 11:30:50 Computer:SCOTT-8879C7D10 , SCOTT-8879C7D10 Username:Administrator , Administrator ---------------------------------- Keys added:2 ---------------------------------- HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices HKU\S-1-5-21-746137067-1409082233-839522115-500\Software\Microsoft\OLE ---------------------------------- Values added:3 ---------------------------------- HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\Microsoft Svchost local services: "Winsec32.exe" HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices\Microsoft Svchost local services: "Winsec32.exe" HKU\S-1-5-21-746137067-1409082233-839522115-500\Software\Microsoft\OLE\Microsoft Svchost local services: "Winsec32.exe"
On startup the malware writes these three registry keys. These keys will ensure that when the computer is restarted the Winsec32.exe application will start as well.
The final thing I looked at was the logs from
vmnet-sniffer. The logs were full of DNS lookup requests for the host name testirc1.sh1xy2bg.NET. My virtual machine was set up in host only mode so the lookup failed. In order to further check the network traffic. I edited the host file on my virtual Windows machine and set the
testirc1.sh1xy2bg.NET host name to point to the IP address of my MacBook’s network interface. After I set the host file my network sniffer started showing the following packets:
174 152.241528 172.16.99.128 172.16.99.1 TCP 1427 > 6667 [SYN] Seq=0 Win=64240 Len=0 MSS=1460 175 152.241588 172.16.99.1 172.16.99.128 TCP 6667 > 1427 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0
126.96.36.199 is the IP address of my virtual Windows XP machine and 172.16.99.1 is the IP address of the VMWare network interface on my MacOSX machine. Port 6667 is the default port for IRC, so the malware was now trying to connect it’s IRC server.
So to summarize, on startup the malware drops a copy of itself called Winsec32.exe into the Windows directory. It creates three registry keys setting the values to the Winsec32.exe. These registry keys are used to auto-start the malware when the system starts up. After that it tries to connect to an IRC server at
What type of command and control server does the malware use? Describe the server and
interface this malware uses as well as the domains and URLs accessed by the malware.
Based on everything that was discovered during the previous two questions, I think it’s safe to say that this malware uses IRC as it’s command and control server. The interface it uses is to connect to a specific server, join the #chalenge channel and then wait for commands. The only domain accessed is that of the IRC server that it connects to which is
What commands are present within the malware and what do they do? If possible, take control of the malware and run some of these commands, documenting how you did it.
The first thing I did in order to answer this question was to set up an IRC server on my MacBook. I download ngircd from http://ngircd.barton.de/. I chose
ngircd because it was small, easy to compile and has MacOSX support. Next I reverted my VMWare machine back to a clean state. I then used mIRC to connect to my MacBook’s IRC server and joined the #chalenge channel so I could watch what happened. Then I ran
malware.exe ran I saw the following entries show up in the ngircd logs:
[1106:6] Accepted connection 7 from 172.16.99.128:2744 on socket 4. [1106:5] User "USA[XP]firstname.lastname@example.org" registered (connection 7)
In mIRC, I saw the following:
I tried sending a couple private messages to the bot but there was no response. I started to look through the disassembly to try to figure out what commands the bot understood. I went back to the output from my
strings command and started looking through it for things that looked like possible commands and where they were referenced from. I started to come across strings like
proc.on. All of these strings were referenced from the same procedure located at
0x00403EF2. I then went through and made a list of all referenced strings in this function. There seemed to be quite a bit of logging messages containing either the string
RealmBoT so I then dropped all strings with either of those two words in it. Next I went through the list by hand removing items that didn’t look like commands and came up with the following list:
Next I started going through the list of possible commands, sending them to the bot and looking to see if I got any response. I went through the whole list and there was no response, so I started debugging the procedure so I could watch what happened when I sent a message. Eventually I stumbled upon this line:
004045A6 3A05 D0C74100 CMP AL,BYTE PTR DS:[41C7D0] 004045AC 897D 28 MOV DWORD PTR SS:[EBP+28],EDI 004045AF ^0F85 B4FDFFFF JNZ Winsec32.00404369
The data at
0x0041C7D0 is the ‘.’ character. If the first character in the command wasn’t a period then the procedure didn’t do anything. So then I went through trying the commands with a period in front of the command. Still no response. Next I started debugging/looking at the login command in more detail. It looked like it wanted a password sent to it so I tried the .login command with a password and got this response:
-USA[XP]8929677- Are you a Fucker?. (email@example.com). -USA[XP]8929677- No pass for you.
After more debugging through the login handling code around
0x004045AF I figured out that the password it wanted was gemp123 and my hostname on IRC needed to be legalize.it. I eventually just ended up patching Winsec32.exe in memory so that it would accept my login. After I was logged in then the commands above started working. See the example session below.
<USA[XP]8929677> [REALMBOT] : Thank for trying. <admin> .httpd.on <USA[XP]8929677> [REALMBOT] << Server listening on IP: 172.16.99.128:80, Directory: \. >> <admin> .ftpd.on <USA[XP]8929677> [REALMBOT-FTP] : Server started on Port: 0, File: C:\WINDOWS\Winsec32.exe, Request: Winsec32.exe. <admin> .proc.on <USA[XP]8929677> RealmBoT (processes.p.l.g) .Â»Â». Listing processes: <USA[XP]8929677> System (4) <USA[XP]8929677> smss.exe (428) <USA[XP]8929677> csrss.exe (660) <USA[XP]8929677> winlogon.exe (692) <USA[XP]8929677> services.exe (736) <USA[XP]8929677> lsass.exe (748) <USA[XP]8929677> vmacthlp.exe (908) <USA[XP]8929677> svchost.exe (924) <USA[XP]8929677> svchost.exe (1004) <USA[XP]8929677> svchost.exe (1116) <USA[XP]8929677> svchost.exe (1168) <USA[XP]8929677> svchost.exe (1328) <USA[XP]8929677> spoolsv.exe (1572) <USA[XP]8929677> explorer.exe (1708) <USA[XP]8929677> VMwareTray.exe (1844) <USA[XP]8929677> VMwareUser.exe (1860) <USA[XP]8929677> ctfmon.exe (1868) <USA[XP]8929677> VMwareService.exe (260) <USA[XP]8929677> alg.exe (1220) <USA[XP]8929677> svchost.exe (456) <USA[XP]8929677> mirc.exe (144) <USA[XP]8929677> Winsec32.exe (512) <USA[XP]8929677> OLLYDBG.EXE (1944) <USA[XP]8929677> idag.exe (1652) <USA[XP]8929677> notepad.exe (3908) <USA[XP]8929677> RealmBoT (processes.p.l.g) .Â»Â». Process list completed. <admin> .prockillid 3908 <USA[XP]8929677> [REALMBOT] << Process killed ID: 3908 >>
How would you classify this malware? Why?
I would classify this malware as a Bot. I would classify it as such since the sole purpose of this program seems to be to connect to an IRC server and await commands.
What do you think the purpose of this malware is?
See the question above. The purpose seems to be to connect to an IRC server and await commands from someone. The malware also seems to be able to attempt to infect new machines via a VNC exploit.
Is it possible to find the malware’s source code? If so, how did you do it?
I was able to find the malware’s source code. The first thing I did was search for “RealmBot” on Google which turned up a lot of hits for a World Of Warcraft bot. So next I searched on google for “RealmBot Malware” (note my use of quotes are just to detail what I searched for on google but I didn’t actually quote my search). The second hit on google had a title of bot source code and mentioned something called crx-realmbot.VNC+RFI. The link however didn’t have the source. I then searched for this more detailed name “crx realmbot vnc download” After looking through lots of results to different RAR files of multiple bots, I came across a link, http://darksun[.]ws/download/Bots/, that let me download just the individual crx realmbot files. After comparing the strings in the downloaded source code to the strings in the malware.exe and comparing the entry point in my disassembly to the WinMain function in the source, I concluded that this was in fact the source to this bot.
How would you write a custom detection and removal tool to determine if the malware is present on the system and remove it?
In order to write a custom detection and removal tool there is only a few things that would need to be done. First, you would want to look at the running processes and see if there are any processes running called Winsec32.exe. If you find this process running then immediately stop it. Even if you don’t see it running the detection program should still go on to the next step. Next look in the Windows directory for a file named Winsec32.exe, if this file is found then it should be deleted. Next the detection tool should look in the registry for the following three keys:
- HKLM\Software\Microsoft\Windows\CurrentVersion\Run\Microsoft Svchost local services
- HKLM\Software\Microsoft\Windows\CurrentVersion\RunServices\Microsoft Svchost local services
- HKCU\Software\Microsoft\OLE\Microsoft Svchost local services
If any of these keys are found then they should also be removed. Stopping the malware from running, removing the executable, and cleaning the registry keys should be enough to remove the malware from the system.