Shifting yourself to space

June 6, 2011

PE in thy blood

Filed under: Uncategorized — shift32 @ 4:42 pm

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June 5, 2011

Spyeye: Father `n Son

Filed under: Uncategorized — shift32 @ 1:45 pm
Tags: , , , , ,

I do not work much on SpyEye, I only get a chance to view it on my days off nowadays, hence the slow progress, but here’s my latest progress with SpyEye.

Also, a short tip before I start digging a bit – I found that the collaboration of IDA and OllyDBG together (if you got two screen [ I don’t have two screen though 😦 ] ) is quite great, how is this possible some of you might ask ?
Well, you can use OllySync + IDA-Sync plugins in order to share comments etc
The plugin is a bit outdated and I plan to rewrite it a bit (though Pedram has done great work)
When trying to set function names in OllySync the IDA-Sync server fails to interpret it well, but comments are amazing and IDA’s analysis adds quite alot of information.

It seems that I was mistaken in my previous post , the function which I stepped into was not the decryption stub of anything, it was only an initial check of the system and grabbing some basic info about what’s what and where
basically, the function consisted of fetching the computer’s name, the windows version, and some other details which are not that interesting for us.

It seems that SpyEye’s resource section play an important role in it’s infection process, section C2 and C3 are the sections which SpyEye holds the compressed configuration and sections SC1 and SC2 (I might be mistaken here with the exact names, but they do reside under the “SC” dir in the resources) hold the parasite code

After gathering all the information SpyEye needs from the basic initialization function, SpyEye creates a mutex and constantly checks for the Volume:\algonic\ directory existence, the reason for that is because that’s where SpyEye creates it’s reboot-killer executable named algonic.exe, it also contains the config.bin which has all the juicy information and plugins one wants to obtain once SpyEye reversed.

SpyEye frequently calls RtlAdjustPrivilege in order to get max privileges and infect processes with it’s parasite (inside the resource dir).
Also – a small hint to those who fear the “600 functions spyeye contains” – the reason SpyEye holds so “many” functions is quite simple – SpyEye doesn’t import/export all the functions it uses, if the author would’ve been smarter, he would’ve used only GetProcAddress and used the PEB to get the kernel32.dll base address
SpyEye uses some sort of “special” macro which uses a classical technique to walk through the dll the function resides in and find it, it has a hardcoded value of the hash it’s looking for and whenever someone wants to call any function it just wraps it around some wrapper function
This could be easily evaded by writing some sort of pattern matching function
Since the function which finds the dll and walks through it is the same, and the push order is always the same to find the function – a simple pattern matching procedure could name all those functions by simple instrumentation

Another thing I wanted to discuss is the infection process, which I found a bit nice,
SpyEye calls CreateToolhelp32Snapshot to get a list of all running processes and walks through them using Process32Next, each time it finds a process which isn’t csrss, smss, or System (which are critical system processes :/) it injects itself into, the parasite injection process is as follows:


1. Spyeye Calls OpenProcess(CREATE_THREAD | VM_READ | VM_WRITE | QUERY_INFORMATION,FALSE,1144 /* explorer.exe */);
2. Called NtAllocateVirtualMemory in the remote process at address 0F60000 (RWE)
3. I started debugging explorer.exe and found the page spyeye is going to inject itself into and set a memory on access breakpoint
4. Spyeye Calls NtWriteProcessMemory
5. Called CreateRemoteThread to create a new thread for spyeye malicious parasite
6. Called WaitForSingleObject to figure out that the thread was injected correctly (?)
7. Called GetExitCodeThread to see if it was injected successfully

After that, the parasite SpyEye injected has finished executing or is executing at the moment, the parasite, from what I’ve seen so far does the following things:


1. open Volume:\algonic\
2. write Volume:\algonic\algonic.exe
3. execute Volume:\algonic\algonic.exe
4. delete the original malware executable using DeleteFileA
5. sleep
6. call ExitThread

I might be missing the whole hooking part, as while I’m writing this document seems to be part I’m currently debugging
As I’ve written previously – SpyEye has a loop which walks through all the processes and injects itself into them, somewhere inside it it performs the hooking process

I hope you’ve enjoyed this although it lacked assembly information, I’ll however try to edit the post and add some assembly code too.

May 31, 2011

The case of the spying eyes: blizzard stubs

Filed under: Uncategorized — shift32 @ 11:17 pm
Tags: , , , , ,

So I finally managed to unpack SpyEye this Saturday, and only today (Thursday) had the time to start actually exploring what it does,
I’ve heard and read from friends and the net that SpyEye got some several interesting modules
also it’s module load – use – unload technique seemed interesting. I’ve also heard that it steals money and performs different kind of phising attacks, all of this seemed quite interesting to research.

I’ve hooked up olly and opened the unpacked version of spyeye, opened the names bar and looked for interesting function to set breakpoints on, I’ve also searched for all intermodular calls and found some (even more) interesting functions

As it seems, SpyEye doesn’t import all the function it’s using in it’s IAT, as when inspecting it with PEiD or anything else you see not many functions

To my humble guess it’s using a simple (yet, known), “trick” of dynamic libary loading, I have first seen it in uninformed and the technique is quite nice (originally by lsd-pl folks)

As olly shown in the “show all intermodular calls” window, it seems

However, be mistaken not – the calls repeat themselves, what really caught my eye was the unresolved call here, I’ve set bp on every possible call outside and started my static analysis journey

I started stepping the code, not running it, to see if there are any interesting things and it seems that the start of the code had some nice spots

The first thing which caught my eye was that SpyEye looks for kernel32.dll by first getting it’s address from the PEB, by walking through it’s linked list, this method is quite known as i mentioned earlier by uninformed ,however, spyeye doesn’t use a loop to look for kernel32.dll it
goes through two values and hopes for the best – if someone put kernel32.dll in a different place in the linked list – SpyEye is a bit doomed (;

The other thing which caught my eye was that SpyEye accesses its .rsrsrc section (resource), it gets a handle to them, changes their permissions and continues onward – this is something which might be pretty interesting

the find.resource calls are to find the specified resource with GetModuleFilenameA function
and the rsrsrc.alter.perm are to alternate the permissions the resource has probably to FFFFF, or something like it, it is still unknown what their purpose is, so I don’t know what to look for

One of the resources starts with a string “!EYE” which hints for some propriatery struct for SpyEye (or perhaps something different ? we don’t know yet)

There’re basically three resource section I got my eye on – C1 C2 and C3, but I didn’t find any usage with/of them for now, so we’ll leave them for now.

Also I found several strings which got my eye glitchy

Remember “algonic” from the previous posts ? this is the name of the child process that our malware creates, as for config.bin – well the name answers for everything, it seems to be some sort of configuration SpyEye has, perhaps it contains C&C IPs and passwords to communicate with our big brother

After stepping more code I’ve found some small jackpot, I remember when I was unpacking SpyEye I got really frustrated when I didn’t know which functions SpyEye was using in order to allocate space for itself, and once I’ve found them – everything went alot easier,
So after stepping some code I found that SpyEye calls NtAllocateVirtualMemory to allocate space for something…something big, as of writing now I have a few clues of what it might be, but I still can’t be sure,
however my guesses go from
1. a huge decryption stub to decrypt the configuration and other resource section
2. a huge decompression/compression stub to de/compress something else
3. something else I have no clue yet (always leave room for the unexpected, hehe)

Why am I not thinking about hooking processes ? because as it seems SpyEye is only going through the tasklist at later stages of the code, I’ve seen a few calls to GetCurrentProcessId, and you are right if you said that it doesn’t prove anything, this is only a guess…I’m writing this while still disassembling everything..
However in order to prove more that I’m right I’ve scrolled down with olly a bit more and found this little interesting (yet, exciting) block :

See the comments olly adds on the side ? see smss.exe, csrss.exe, services.exe, etc ? does this look to you like something that would’ve done after we hook things up ? This looks like a prologue to something…something interesting (:

I kept stepping the code until I reached the copy of a resource section, however, the rest seems to be like a topic for another post,
To be continued(:

May 28, 2011

The case of the spying eyes: The third eye

Filed under: Uncategorized — shift32 @ 4:52 pm
Tags: , , , , , , ,

About an hour ago I managed to fully unpack SpyEye, my work was stopped due to other commitments but this morning I promised myself that I’ll try finishing the initial analysis.

The sample I have of SpyEye is triple packed with three layers of known packers, the configuration stub crypto and probably anything else is totally different topic

UPX is quite easy to unpack, basically when you hook up olly you begin at the regular “pusha” instruction

The first thing you gotta do is just scroll down until you meet lots of “db 00”
and set a breakpoint at

sub esp,-80
jmp entryPoint

This would be the last jump before you hit the entry point of the executable, in our case – we’ll hit the ep of ASPack, since my sample is triple packed

In order to get the decryptor stub, we’ll be setting a breakpoint at VirtualAlloc, as this is the function which is used to allocate the space for the function,

Once we hit VirtualAlloc, we’ll step over and return to the caller, we could see where the decryption stub will be written to by the return value of eax

So we set a memory bp on the address eax points to and run –
we hit one rep stos instrcution which copies the decrypted stub into the location and hit step over to complete the copy process

Right now we have the function which decrypt the real (packed with UPX) exectuable code, I’ll try to analyze it once I’ll finish the global analysis, in order to get to the real entrypoint, we have two possibilities:
1. Step the code and look for interesting writes and reads
2. Set a bp at the function which allocates space for the EP

The first option would work if we didn’t know which function is used to allocate the EP, however it would be tedious work.
The second option is quite easier, as assuming we don’t know which function actually writes the EP code, we set a bp on every interesting allocation function, this includes – (amongst others) – VirtualAlloc, VirtualAllocEx, NtAllocateVirtualMemory, GlobalAlloc, HeapAlloc, etc
I’ve had a few hints from friends and managed to figured that the function is ZwAllocateVirtualMemory

I’ve set a bp on ZwAllocateVirtualMemory and hit F9 in olly, the first occurrence was the routine which copies the decrypted PE.

Once the PE was written to it’s original place just hit twice “execute till return” and you’ll hit a ret that get you into ZwFreeVirtualMemory, return there and you’ll hit the EP
You’re now in the EP of the UPX packed code, as this is – once again – quite easy to unpack –
just jump to the real EP and have fun

To be continued.

Edit: the post is a bit messy, I’ll rewrite it later on

May 25, 2011

The case of the spying eyes

Filed under: Uncategorized — shift32 @ 10:48 pm
Tags: , , , , , ,

I found this sample of an interesting spyeye malware packed with UPX and ASPack,
and decided to reverse it on my own.
As I’ve never unpacked ASPack I decided to look around and found two interesting anchors,
both are interesting win32-api memory allocation functions which are called VirtualAlloc and ZwAllocateVirtualMemory

But before reversing the malware itself I wanted to see what goes “on the hood”, as Mark Russinovich documents in his blog
In other words – before dwelling into an unpacking nightmare I want to see what sort of files it adds to the system, what registry keys it modifies, what sort of hooks it adds etc

So onward my small journey I’ve hooked up several processes (sysinternals + rku, rootkitRevealer)
I’ve set a snapshot on the vm to return to my initial status after executing and executed the binary

And there I’ve had it, after just executing it everything remained the same, I’ve looked at procmon and regmon to see what sort changes in their process tree and started investigating.

Before running the malware I’ve used shellrunas to first run the malware in a Guest user restricted mode, just to see how it handles things, and I saw that the malware forks itself to a new process called “algonic.exe”,

I’ve set the process in suspended mode and started looking at the log of procmon to see which values it tried modifying

Considering that the malware doesn’t have any zerodays it couldn’t leave Guest user, and execute code in ring0, this helps a bit as I know I’m dealing with any kernelmode malware

Now onto the interesting part, I’ve looked at procmon and saw that the process fork itself and looks for certain specific registry values such as ComputerName,
“HKU\S-1-5-21-1547161642-152049171-839522115-501\Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders” ,
“HKU\S-1-5-21-1547161642-152049171-839522115-501\Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders\Cache” , “HKLM\SOFTWARE\Policies\Microsoft\Windows\Safer\CodeIdentifiers\Paths\{dda3f824-d8cb-441b-834d-be2efd2c1a33}” etc,

it tries to lower down the security attributes ie has, open different know dlls (ntdll, wininet, usp01 (??), windows Shell manifest etc),

At this time of writing I do not know the purpose of all those, I can only think it wants to hide itself (with hooks, though), and add different malicious things
I can also ponder that it tries to collect information about the system, if the malware is smart enough it will detect that it’s running inside VirtualBox ( as vbox has two main processes with *vbox* initials inside them, though there are other ways to detect you’re inside a vm like timing-attacks etc )

One interesting thing my eyes caught was that the malware tries to read the

E:\Documents and Settings\Guest\Application Data\Microsoft\SystemCertificates\My\CRLs

This path is quite important as it includes the local system certificates the user has, adding the virus’s certificate to the trusted path will probably break any av or scanner that tries to look for malicious things automagically

Aight, enough for that now –
Let’s move onto the real binary – the algonic.exe which seems to do all the dirty job
[btw, as this time of writing, since no dynamic/static analysis of the binary is done, it is quite unknown what the malware is looking for, I can only assume that I’m missing alot of under the hood stuff, but that’s only an assumption which must be analyzed and faced ]

The algonic.exe is located in the same root drive the malware was originally located, in my own situation it’s located in

 E:\algonic 

The folder is secret and probably well protected if ran with administrator privileges.
The folder contains to files – algonic.exe and config.bin

I’ve hit PEiD on algonic.exe and I wasn’t surprised to see that it is indeed also packed with UPX and
probably also with ASPack,
at this point I’ve unpacked the UPX packing protection by simply putting a bp at 497F3 which is probably the most classical way to unpack most UPX versions

I’ve set also two hardware breakpoints – one for each unique function I was hint’ed, one for VirtualAlloc and one for ZwAllocateVirtualMemory,

Once I’ve hit both bp’s I’ve managed to get the decryption stub, and also the function which calls the EP, I’ve seen the real PE header (at 0x4000000) and currently I’m reversing the last part of the loop before reaching the last popad + ret part.
(I do want to apologize for not writing too much about this phase, but since it’s incomplete I’m still unsure what I am missing and what’s not)
Wish me luck.

To be continued

May 23, 2011

Nanomites – First thoughts

Filed under: Uncategorized — shift32 @ 4:19 pm

After reading about nanomites I got quite excited and thought about implementing it on Linux
I thought it would quite easy, however it didn’t seem as the development started.

My work was basically based upon signals, whenever an application hits a signal
it goes to a signal handler, either registered by the parent process (debugger, etc)
or that the executable itself has it’s own signal handler

Signals are not a vague topic in Linux and there’s full documentation, I read a few papers about them and started working

1. SINGLESTEPPING with int $3

The basic idea was this –
1. Executable executes it's instructions one by one.
2. A signal handler is registered to handle interrupt traps
3. When the executable hits int $3 - Interrupt Trap the signal handler is executed
3.1 The signal handler check its tables against the current EIP to see whether or not it's a nanomite
3.1.1 Assuming it is a nanomite - the handler replaces the instructions of int $3 with the real instructions
3.1.2 The handler transfers execution to the executable to continue its journey

Problems –
1. When an int $3 is occured the program stops :/ so you can’t do anything
2. It’s not that easy to replace instructions due to sizes, int $3 only takes two bytes, while the real instructions might take more…

The solutions I tried going with were basically these:
1. Use PTRACE (shrug, I know) interface in order to single-step the executable and look for “cc” opcodes (int $3) using PEEKUSER parameter in the ptrace(…) function
2. The instructions after the int $3 will be padded with nops/garbage so we could replace them upon runtime

2. Using a different signal than int $3

I chose a random signal than int $3 and hoped for good, the idea was basically the same except this time I wasn’t using ptrace() at all
The problems which occured were that I was unable to write code to the running process and thus had to continue execution in my own huge char tables[c0de] = { “\xcd\x80”} array

3. Section permissions

This is a theoretical idea which I read that was implemented in the Shrinker packer (win32)
We set our section permissions to non-readable/executable and once a signal is raised we check our tables

Every packed section is encrypted and has no read/execution permissions
Each time there’s a jmp a section without read/execution permissions a signal is raised
We intercept the signal and on the fly decrypt one instruction at a time (and not the whole section, to avoid cold memory attacks) and execute it on the fly
The section remains encrypted and once its execution is done we set back the permissions to non-readable/execution

I haven’t started implementing it yet but it seems quite interesting work.

Stay tuned (:

May 21, 2011

Push `n call

Filed under: Uncategorized — shift32 @ 8:43 pm
Tags: , , ,

I’m no glorious reverser, however I’m always glad to learn some cool new technique to
detect interesting behaviour
As my journey reversing for fun and non-profit I got into different methods to call a function
in an “obfuscated” way

Such way that in most cases you won’t be able to know where the call would actually go to
The actual value of the call is decided upon runtime and is based on the value of a few things
The actualy value of the call is decided upon runtime and is based on usually one of things below:

1.The value of the register
For example – let’s take a look at this simple method

mov eax,[ebp-22]
shl eax,3
call eax

in this example below the value of ebp-22 can be calculated upon runtime
but if we’d try to statically analyse the function it will be quite hard to follow the stack changes and call
as this example is quite abstract, most malware add different kind of obduscation methods
such as different calls to useless function and register manipulation

2. push `n ret

push 5
push &exit
call obfuscation_method
ret

In this example it gets a bit trickier, obfuscation_method doesn’t really interest us
since once we’ll comeback from obfuscation_method, we’ll be back to the previous stack frame
and since we’ve pushed the address of printf beforehand – we’ll return to it immidiately after calling obfuscation_method

3. nopsled, bruteforce

In this specific method we don’t really know at all (nor does the program itself) where are we going
The method is based on a simple “brute-force” loop which tries calling addresses by simple arithmetic manipluation

mov eax,&base_offset
mov ecx,MAX_BASE_OFFSET
call [eax+ecx]

in this specific method we’ll have to allocate an array of MAX_BASE_OFFSET
pad it with nops or garbage instructions and add our real code in specific location for example

nop
nop
nop
nop
nop
[ ... real code goes here ... ]
ret
nop
nop
nop
nop
[ ... more real code goes here ... ]
ret
nop
nop
nop
nop

it is quite hard (and frustrating) to know where the real code is especially if don’t have nops and real garbage code the disadvantage in this specific method is that you must align you code perfectly else you’ll get an exception of an invalid instruction

this method is quite equivalent to a malware which doesn’t know it’s decryption key (same concept) and so it just bruteforce’s itself until it finds the key the disadvantage here is that you’ll need large computation power in order to get they decryption key when not dealing with the classical xor/XTEA/etc crypto

4. nanomites

I’ve read about this method in peter ferrie’s article and decided to try to implement it on my own
From Peter Ferrie’s article :

Nanomites are a more advanced method of anti-dumping.
They were introduced in Armadillo. They work by replacing
branch instructions with an “int 3” instruction, and using
tables in the unpacking code to determine the details. The
details in this case are whether or not the “int 3” is a
nanomite or a debug break; whether or not the branch
should be taken, if it is a nanomite; the address of the
destination, if the branch is taken; and how large the
instruction is, if the branch is not taken.
A process that is protected by nanomites requires selfdebugging
(known as “Debug Blocker” in Armadillo, see Anti-Debugging:Self-Debugging
section below), which uses a copy of the same process.
This allows the debugger to intercept the exceptions that are
generated by the debuggee when the nanomite is hit.
When the exception occurs in the debuggee, the debugger recovers
the exception address and searches for it in an address table. If a match is found, then
the nanomite type is retrieved from a type table. If the CPU
flags match the type, then the branch will be taken. When
that happens, the destination address is retrieved from a
destination table, and execution resumes from that address.
Otherwise, the size of the branch is retrieved from the size
table, in order to skip the instruction.

This method however adds much more complication to the code you’re writing
and divides it into separate projects:

One is your original project which has all the code you’ve written originally

The other is a “stub” ( those who ever wrote a packer would know this acronym better than I do) that keeps track of the nanomites and knows when a real nanomite is hit and not a regular int 3 instruction caused by the debugger / compiler.

The third is a project that injects the stub ( PE/ELF file manipulation, adding a new section if necessary ) and replaces the calls/jmps
with nanomites (int 3 instructions)

This is a whole new level of complication and it really frustrates the reversing process, not talking about that it is really hard to statically reverse such binary
without having all the instructions in your hand….

April 28, 2011

Dwelling into ZwSetSystemInformation

Filed under: Uncategorized — shift32 @ 4:34 pm
Tags: , , ,

As things got a bit out of control with my simple driver, I have decided to debug and see what’s going on really inside ZwSetSystemInformation.
Perplexed by the windows architecture (so far I was used to good old Linux 2.6.x ), I’ve plugged windbg
into a session an


kd> uf nt!ZwSetSystemInformation
nt!ZwSetSystemInformation:
804fe534 b8f0000000      mov     eax,0F0h
804fe539 8d542404        lea     edx,[esp+4]
804fe53d 9c              pushfd
804fe53e 6a08            push    8
804fe540 e80ce10300      call    nt!KiSystemService (8053c651)
804fe545 c20c00          ret     0Ch
kd> x nt!ZwSetSystemInformation
804fe534 nt!ZwSetSystemInformation = <no type information>

As I’ve read beforehand, ZwSetSystemInformation is an undocumented and “stealthy” function to load drivers, so I wasn’t looking for anything special
as the “examine” command doesn’t give anything at all, I’ve kept looking a bit more – I thought about checking out where the function is defined in the official sources – aka – Microsoft
or the WDK but it seems that undocumented is indeed undocumented, the best I could find was basically the original definition I had


NSTATUS (_stdcall *ZwSetSystemInformation)(	IN DWORD functionCode,
											IN OUT PVOID driverName,
											IN LONG driverNameLength );

and nothing more than.
Well, I guess that it’s enough for a start, I’ve a set a bp in ZwSetSystemInformation and kept hoping for good.

kd> bp nt!ZwSetSystemInformation
kd> bl
 0 e 804fe534     0001 (0001) nt!ZwSetSystemInformation

Once I’ve hit it, I’ve disassembled the call and wasn’t too surprised to see that it was calling to nt!KiSystemService

nt!ZwSetSystemInformation:
804fe534 b8f0000000      mov     eax,0F0h
804fe539 8d542404        lea     edx,[esp+4]
804fe53d 9c              pushfd
804fe53e 6a08            push    8
804fe540 e80ce10300      call    nt!KiSystemService (8053c651)
804fe545 c20c00          ret     0Ch

The interesting arguments here are

804fe534 b8f0000000      mov     eax,0F0h
804fe539 8d542404        lea     edx,[esp+4]
804fe53d 9c              pushfd
804fe53e 6a08            push    8

I don’t know enough to understand what each one of them means, but it’s worth a shot investigating deeper in order to understand

Trying to figure what is the address which gets into edx didn’t give much results beside archaic thoughts


kd> dw 81dc4068 
81dc4068  0006 0070 0000 0000 4070 81dc 4070 81dc
81dc4078  4078 81dc 4078 81dc 6000 f4ca 2000 f4ca
81dc4088  d000 7ffd 0000 0000 5b10 f4ca 0200 0000
81dc4098  0a00 0800 409c 81dc 409c 81dc 40a4 81dc
81dc40a8  40a4 81dc 2da0 8201 0000 0000 076e 0000
81dc40b8  0000 0000 0000 0000 0000 0000 40d8 81dc
81dc40c8  0000 0000 8db8 8054 5c6b 0001 0008 0400
81dc40d8  bbf8 81f2 bbf8 81f2 4068 81dc 3a60 f72a
kd> db 81dc4068 
81dc4068  06 00 70 00 00 00 00 00-70 40 dc 81 70 40 dc 81  ..p.....p@..p@..
81dc4078  78 40 dc 81 78 40 dc 81-00 60 ca f4 00 20 ca f4  x@..x@...`... ..
81dc4088  00 d0 fd 7f 00 00 00 00-10 5b ca f4 00 02 00 00  .........[......
81dc4098  00 0a 00 08 9c 40 dc 81-9c 40 dc 81 a4 40 dc 81  .....@...@...@..
81dc40a8  a4 40 dc 81 a0 2d 01 82-00 00 00 00 6e 07 00 00  .@...-......n...
81dc40b8  00 00 00 00 00 00 00 00-00 00 00 00 d8 40 dc 81  .............@..
81dc40c8  00 00 00 00 b8 8d 54 80-6b 5c 01 00 08 00 00 04  ......T.k\......
81dc40d8  f8 bb f2 81 f8 bb f2 81-68 40 dc 81 60 3a 2a f7  ........h@..`:*.
kd> 
81dc4068  06 00 70 00 00 00 00 00-70 40 dc 81 70 40 dc 81  ..p.....p@..p@..
81dc4078  78 40 dc 81 78 40 dc 81-00 60 ca f4 00 20 ca f4  x@..x@...`... ..
81dc4088  00 d0 fd 7f 00 00 00 00-10 5b ca f4 00 02 00 00  .........[......
81dc4098  00 0a 00 08 9c 40 dc 81-9c 40 dc 81 a4 40 dc 81  .....@...@...@..
81dc40a8  a4 40 dc 81 a0 2d 01 82-00 00 00 00 6e 07 00 00  .@...-......n...
81dc40b8  00 00 00 00 00 00 00 00-00 00 00 00 d8 40 dc 81  .............@..
81dc40c8  00 00 00 00 b8 8d 54 80-6b 5c 01 00 08 00 00 04  ......T.k\......
81dc40d8  f8 bb f2 81 f8 bb f2 81-68 40 dc 81 60 3a 2a f7  ........h@..`:*.
kd> u 81dc4068 
81dc4068 06              push    es
81dc4069 007000          add     byte ptr [eax],dh
81dc406c 0000            add     byte ptr [eax],al
81dc406e 0000            add     byte ptr [eax],al
81dc4070 7040            jo      81dc40b2
81dc4072 dc817040dc81    fadd    qword ptr [ecx-7E23BF90h]
81dc4078 7840            js      81dc40ba
81dc407a dc817840dc81    fadd    qword ptr [ecx-7E23BF88h]
kd>

So I kept on debugging .. to be continued for now….

Short tips: Debugging a vm with a named pipe

Filed under: Uncategorized — shift32 @ 12:59 pm
Tags: , ,

I recently started writing drivers with windows, so far I’ve only written one and you can see the results down below, however I tried loading the driver in a non-traditional way using the undocumented ZwSetSystemInformation

For some unknown reason, the driver halts the system and I get an exception of an invalid instruction
However this is not the case of this post

In order to debug things correctly, I’m using VirtualBox winxp-sp2 as a guest machine to run my code and my host machine runs a windbg session
VirtualBox’s support in com ports sucks and I didn’t make it at configurating a com port for my debugging session so I decided to use named pipes

In order to do so, go to the Settings -> Serial Ports – >
Check the “Enable serial port” and create “Host Pipe”

It is quite crucial that you’ll name your pipe as \\.\pipe\ since if not you’ll get an error while running the vm

Once you’ve created a named pipe, run

kdsrv.exe -t npipe:pipe=\\.\pipe\<pipe_name> in your guest machine

within the host machine go to File -> Kernel Debug ->
and choose “Port” within the COM box write your named pipe name, Check “Pipe” and you’re done.
You can also check “Reconnect” too, it saves a few things

Once you load up the os in debug mode (bcdedit etc) be sure to hit ctrl+break to halt the system and get control
It’s also noted to use the symbol server that ms offers in order not to fuck symbols up (it’s quite a nightmare setting things up imho)

enjoy.

April 17, 2011

The case of video.exe

Filed under: Uncategorized — shift32 @ 5:46 pm
Tags: , , ,

The case of video.exe

Just another day without much work and I wanted to do some fun reversing. I fetched some malware from malc0de.com database and started investigating.

The malware is packed, and from the begining it has a few annoying anti-debugging stuff, however IDA knows how to deal with them and with a little bit of editting in olly
everything can be overrun

loc_49C8F4:                            ; CODE XREF: start+9A7B6_j
.data:0049C8F4                 jmp     loc_49C8FD
.data:0049C8F4 ; END OF FUNCTION CHUNK FOR start
.data:0049C8F4 ; ---------------------------------------------------------------------------
.data:0049C8F9                 db 22h, 9Eh, 8Dh
.data:0049C8FC ; ---------------------------------------------------------------------------
.data:0049C8FC                 sahf
.data:0049C8FD ; START OF FUNCTION CHUNK FOR start
.data:0049C8FD

Notice the db 22h, 9eh and 8dh which resolve to

simple assembly obfuscation

Olly gets a little bit crazy when hitting the single step button, these anti-debuggin tricks appear all along the way

I’m writing this documentation while still disassembling the malware and so far I’ve ran into several xor-loop decryption
It seems that the crucial parts of this malware are encrypted with a simple xorl-loop encryption method, which is quite easy to spot

simple xor decryption loop of a code chunk

EAX seems to hold the address that will be decrypted, EBP holds the relative address and makes it a true virtual address
DL/EDX seems to hold the decryption key (70h) and ECX as always has the len

The malware continues it’s journey and allocate space at 0x00BEE00, without any known reasons (for now ? : )

It seems that every decryption method is quite similar to the other, only they’re written over and over
DST address is always in either EAX or EDX (depending on the size word,dword,byte, etc),
KEY is always in either EAX or DL which seems to be 0 most times
LEN is always in ECX

after these arguments are pushed onto the stack they’re moved into the registers and a simple mov-xor-dec-jnz loop begins

Next there’s an interesting PE header deobfuscation method, the method is very long and I still haven’t fully understood how it works
but the main thing it does is copy an obfuscated PE header from ESI to EDI using AL as the register holding the chars and DL as the state machine
The method consists of MANY JNB/JNZ and ADD/ADC’s with DL which makes it even harder to understand what’s going on and why

Once the DOS stub header is reconstructed, the basic PE header is copied along with the section names, size, and virtual addresses of the real executable
They’re all located from 0x00EB000.
There’s an interesting side note here to say, if you’ve been disassembling the binary with me, you’d notice that EB0000 plays an important role here, it is chunk we’ve allocated
somewhile ago with VirtualAlloc in 0x49C436

I didn’t follow all of it, I just ran through it managed to copy all the DOS header and the PE header,
once we return – the packer starts fixing regular jmps (E8,E9) and JMP DWORD (25FF), the loop itself is quite easy
it starts from the DOS stub looking for these bytes, if they exist, it just changes their values

fix jmps

Afterwards another PE header is parsed and copied, this time it’s a DLL type PE header, all the sections are copied into the executable and the original PE header is freed with VirtualFree (00BEE0000)

This is probably the end of part I in this series, I hope to continue and reverse this malware and actually see what it is doing

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