How to crack Conseal PC Firewall in an 'unusual' way
(Hooking API calls via IAT)

  

18 September 1999

By NeuRaL_NoiSE

a 1999 RingZ3r0 production
advanced
Advanced
tools used:
  • SoftIce v4.00
  • BoundsChecker v6.01
  • Hacker's View v6.15
  • Procdump v1.5
  • OpGen v1.0b
  • Tasm v4.1

 

( )Beginner (X)Intermediate (X)Advanced ( )Expert

 

 

 

Courtesy of Reverser's page of reverse engineering
lo reverser,

i'm aware of your (correct imho) criteria of "non-targeted" essays...i find
it stupid that STILL now there are essays that won't teach you anything new,
and most of the tutorial writers cant come up with brand new ideas or
such...but, in this case i chose to write something target-related as this
conseal pc firewall tutorial just because...well, just because i followed a
non-usual approach, which is always a good thing...i implemented an IAT hook
trying to explain the basics of it, exploited a mempatcher to patch the hook
inside the import table, injected the hooking routine code in 00-byte caves
between the object table and the first section's raw data in order to avoid
an obvious decryption-due code modification, without actually adding a
bloated 200 bytes raw section...i mean, i think i came up with something
new...a more 'funny' way of cracking stuff...a 'reversive' approach that
hopefully will open most young reversers minds...woah,
well i'm floating a bit too high there, better to get down again ;)
anyway you get the drift: no matter which target it is, the important is
what i did here... if only 2 more persons tomorrow will be aware that you CAN
hook api calls inside a pe file via IAT hooking thanks to this modest
writing, that would make me the happiest person on earth.

laters,
nN.
A great essay by a fine reverser! Italian crackers sublimissimi and machiavellici!
Note how good reversers don't simply breakpoint everything in sight to patch a target, but actually STUDY its less common features in order to understand deeper truths! Wanna start to understand what's like to reverse as it should be? Read this. Enjoy!
Of course, as you all (should) know, once you master such kind of import address table reversing you will also be able to work for your favourite "dll taming" projects... eheh... ad astra per aspera!


Part 1: Intro


Hi everyone...

What does it mean "in an unusual way" ? If u're wondering about it, after reading the title, here is the explanation... it's quite some time that i don't crack anymore, like my friends know, and i prefer to dedicate to the (imho) much richest, more interesting and intriguing Reverse Engineering scenario... meanwhile, tho, among a chat and a nuke to a friend i happened to notice that my precious firewall (Conseal PC Firewall, i think it's one of the best ones even if i know shit about that) goes down... license has expired ?? ohh SHIT, my license has expired! =)

Typical background for a common quick crack (i haven't been settling for long cracking sessions for quite a while...), neverthless i soon realized that there were some good aspects that led to something nicer than a plain serial or a jz/jnz check...

Let me just say that this tute will be as short as possible (not for the fact that it's 4.30am here and i'm quite tired, but because i don't really want to flood you with tons of text....let's try =)

 

Part 2 : Da Crack.


Ok, this is the story.

The program, once expired, and once ran, doesn't make you suspect anything, when, after like 2/3 seconds, voila' a msgbox that tells us that we have finished our time =/... Oh btw i use version 1.37. As i was saying, there's a msgbox, but we won't break on messageboxa, we said we wanna have fun, no usual stuff. So let's open boundschecker and launch frw.exe, being careful to all the api's used... if u are careful enough and u collapse every thread created at the start of the program, u'll notice 6 initial threads and, right before the nag pops, the creation of a seventh thread. Interesting, let's take a look at this 7th thread... u'll notice an overwhelming amount of registry poking, quering and so on, well nothing strange, nothing changed, as bob marley put it... But let's take a look at the values being checked... uhm, u'll notice a certain repetition of LicenseInfo, LicenseID etc... let's open regedit for a second and look for LicenseID... deh, a nice trio of interesting keys... LicenseCode contains probably the encrypted version of the installation date + other various rubbish, LicenseID has a default string for our universal license, LicenseInfo with various unidentified trash... uhm, what are we gonna do ? a coupla bpm's, looking for the decrypting routine, and we write our l33t crack ? NO :)

We said in an unusual way... so let's close regedit (dunno about you, but i'll reserve the decrypting routine for the next time, might be an interesting algo)... anyway, as we were saying, let's come back to our 7th thread, re-popping boundschecker again. Browsing a bit downwards among the api calls, we'll reach a zone where a heap gets allocated+freed, then OH! what's that GetLocalTime =) yup, it's this easy... GetLocalTime gets the current date and hour... then it's obvious that the program decrypts the LicenseCode key, gets the installation date, and then makes his calculations... What are we gonna do ? we could patch the checks in a quick and dirty way, but we talked about having fun, no?? So... let's close boundschecker after a quick look at the rest of the (useless) api calls... open the file with Hiew... wow a little surprise for us, there's a .WWP32 section... the file is packed with wwpack 32... procdump unpacks it i think... but we are hard headed... we want the packed file, wich is cooler and less space-consuming ;) at this point a little pervert thought crossed my mind... let's see... GetLocalTime. Gets year, month and day... I installed Conseal the 17th of July 1999... if i make him believe that it's always the 18th of July 1999 we'll all live in peace... it would be interesting, but how to do it ? uhm, the solution is easy... a IAT hook that intercepts every GetLocalTime call and that fakes the result... easy to do, just that the file is packed, so the problems are basically 2: one, how to install the hook, and two, WHERE to inject the hooking routine... well, installing the hook is as easy as smoking a cigarette, neverthless the situation was interesting and i thought i'd keep walking this path :)

IAT hooking is basically, really, really easy in the concept. I assume that the reader has a medium knowledge of the PE structure, and that he/she knows what an Import Table is... if not, may i suggest you to read some good doc, the best ones are imo Pietrek's and Luevelsmeyer's (whose famous pe.txt i included)... Now, we know that in the Import Table there's an array called FirstThunk, which gets patched at runtime with the addresses of the functions that the program imports... the concept of IAT hooking is based on this: you retrieve the spot that concerns the function we want to hook, and you patch the VA of our hooking routine inside it. This done, when the program will call the function (and thus will pass for the deviation inside the Import Address Table (aka FirstThunk array)), instead of running straight towards the kernel woods, it'll run towards our injected routine's lair... at that point we'll quietly examine the passed params, we forward them to the kernel, or we keep them, or we reset the system, or we make a window pop up saying "Moonshadow is gay =)" or whatever else pleases us ;) (jk mun:P)... well, u got it. Obviously, we can as well fake the result of a call, in our case GetLocalTime, returning to our dear friend frw.exe the perpetual date of 18th July 1999 :)

There's a problem anyway. The file is packed... how and where to inject a hooking routine ? Well, the first idea that popped in my mind was writing a small hooker .exe, then, from within a memory patcher (unavoidable as we'll see) mapping it into memory and access to it from the unpacked process... easy to do since MMF's are mapped in the shared region of the linear address space, thus we wouldn't need any additional context switching routine etc... but then i thought, is it really worth it ? let's make something quicker =)... i wanted to physically patch the routine inside frw.exe, and there was only one place safe from the fury of the storm caused by a decrypting stub that devastates the initial image of the file with his mathematcally cold decompression/patching... i'm talking about the so called caves... this term is particularly familiar to virii writers... caves are those empty spaces (in reality filled with 00-bytes) inside a PE file, in other words 'dead' spaces you can use for any code injection purpose... in our case, not viral code but a nice hooking routine :)

Which cave are we gonna use ?? well, i'd say that the one between the Object Table and the first section's raw data will do fine... open the file with Hiew, just to make an idea... after the stub (this proggie can't be run in dos mode) and the PE,0,0 signature we get the first file header data, then the optional header etc... browsing downwards we find the object table (.text with the relative data, .rdata with its data etc...) ... then we have a succession of zero bytes (our cave) starting from offset 268h and finally we get to .text section at offset 1000h... all this space isn't used/relocated/modified at all, by wwpack32's loader... now you have an idea of what we're gonna do... you choose wether to keep reading or to destroy this htm file ;)

So..so... what do we need now ? Well, considered that we have to install a IAT hook, we need the decrypted image of the file.. in reality we have a 'notionistic' need of a coupla virtual addresses, that we'll be able to stick as patchspots from a memory patcher, even if the file we'll use will always be the packed one... so we open procdump, and we start conseal... as soon as the process has been fired, press the right button inside procdump's tasklist and select Refresh list... here comes a new process, frw.exe... Quickly, right button on the taskname and then "Dump (Full)"... save the dump in a file, and close frw and procdump. That file contains the image of frw.exe exactly as it appears once mapped+decrypted... now the problem is climbing to the import table, and then dwelling inside it until finding the FirstThunk array's dword realtive to GetLocalTime's address... and this implies a DAMN BORING (at least for me) search... so what do we do ? well, some time ago i got really sick of this situation (i had to face it every time i wanted to patch an api call inside a process... which is a rather common thing when u reverse programs, and i had to manually look for the spot in the IAT), and i decided to write a small tool, that i called OpGen, which contains another quite useful function too, it pratically generates opcodes for patching far jumps, only given the starting and the destination VA/RVA (hiew sux when it comes to far jumps)... but we're not interested in such feature, neverthless the little IT scanner that i put into it is useful here, it gives you the patchspot for every function in a snap... seen that i included it in conseal.zip, open it and choose Lookup Imports for patching... select our dumped file and what u'll get (among other things) will be this:

GetLocalTime == call dword ptr [46459C]

Oh, interesting :) that ([46459c]) is the place where we'll stick the address of our hooking routine... Here we are at the point where we face the need of a memory patcher. Having to patch the hook inside the decrypted image of the file, let's open our dear Ultraedit with Tasm support (tm;) and let's begin writing down some code...

 

.386p
.model flat, stdcall

extrn   ReadProcessMemory       :PROC
extrn   WriteProcessMemory      :PROC

UNICODE = 0
include winsux.inc

 


.DATA

        exe_name            DB      "frw.exe",0

        processInfo        PROCESS_INFORMATION     <>
        ini_info                STARTUPINFO                          <>

        iat_hooking_routine     DD      04002A0h        ; VA OF THE HOOKING ROUTINE (IN THE CAVE BETWEEN THE OBJECT TABLE AND                                                                                        ; THE .TEXT SECTION)
        funct_va                         DD      0
        dummybuffer                  DB      0

 


.CODE

start:

        call    CreateProcessA, OFFSET exe_name, 0, 0, 0, 0, NORMAL_PRIORITY_CLASS,0 ,0 ,OFFSET ini_info,OFFSET processInfo
        test    eax, eax
        jz      @@end

; we'll wait for frw.exe to be loaded and unpacked with a little loop (even if we're not able to hook every GetLocalTime there's no problem, the ; ones we effectively need are the ones in the 7th thread, remember)

        mov     ecx, 100000000
        
        .WHILE  ecx != 0
          dec   ecx
        .ENDW

; we retrieve the effective address of GetLocalTime in the kernel directly from the IAT of the unpacked process
        call    ReadProcessMemory, [processInfo].pi_hProcess, 046459Ch, OFFSET funct_va, 4, OFFSET dummybuffer

; now we patch this address in a dword (@ 4002dd) that we'll call from the hooking routine when we wanna call GetLocalTime
        call    WriteProcessMemory, [processInfo].pi_hProcess, 04002DDh, OFFSET funct_va, 4, OFFSET dummybuffer

; and finally we'll effectively install the hook in the FirstThunk array, modifying the address that the program will call inside the IAT
; with the address of our function (in the iat_hooking_routine dword)
        call    WriteProcessMemory, [processInfo].pi_hProcess, 046459Ch, OFFSET iat_hooking_routine, 4, OFFSET dummybuffer

@@end:
        call    ExitProcess, 0                 ; our job is done... now everything is in the hooking routine's hands (bytes:)

 

end     start

 

very good.

At this point, once we compiled the program we'll have our mem patcher that creates the process, waits a bit, then retrieves GetLocalTime's address from the IAT, then patches it inside the hooking routine, and in the end installs the IAT hook in the decrypted image of the program.

now we only have the problem of the hooking routine. What do we need to put inside of it ?

enter Softice and put a bpx getlocaltime... start conseal pc firewall, and press f12 at the first pop. Write DD and then D ESP-4. This will show you the address that has been pushed on the stack before the call GetLocalTime (you can also find it by tracing thru kernel until that "mov ecx, esp-c" (the fifth codeline in the function) where u'll find, in ecx, the same address. Anyway, as i was saying, type "d address" and u'll get the dump of the SYSTEMTIME structure, that gets filled with data concerning current time and date. Let's take a look at it's definition:

typedef struct _SYSTEMTIME {  // st  
    WORD wYear;
    WORD wMonth;
    WORD wDayOfWeek;
    WORD wDay;
    WORD wHour;
    WORD wMinute;
    WORD wSecond;
    WORD wMilliseconds;
} SYSTEMTIME;

uhm, uhm... remember that we have to make the proggie believe that it's always the 18th of July 1999, in other words we have to modify the first, second and fourth Word in the structure... making them respectively 7CFh (1999 dec), 7, and 12h (18 dec)... if u wanna get a close look at the struct, give a DW and then analize it... u'll see how easy this concept is.

So, let's make a lil summary. What will happen is this: the program will call the IAT thinking that it's calling GetLocalTime, while the control will be passed to our hook routine (at 04002A0h)... at that point our situation will be this: we'll save EAX pushing it and then [ESP+4] will hold the return address for the program's code, and we'll save it in a physical dword to call afterwards for the return (the same thing we did from the mempatcher for GetLocalTime's address)... then we'll pop EAX and we'll increase the stack pointer of 4 bytes... at that point [ESP] will point to the SYSTEMTIME structure... so we'll effectively call GetLocalTime... at the return, we'll have, in [ESP-4], the address of the SYSTEMTIME structure, and we'll start modifying it... but first we'll save the value of EAX in a third physical dword (we can't push it because often, if you analize the code flow with softice, the VA of the structure is dangerously close to the stack pointer, so a badly placed push could ruin the struct and crash the program) and we'll stick the VA of the struct inside it... at this point, we'll modify the words relative to year, month and day, then we restore EAX and we jump to the return address, that we saved at the beginning of the routine...

now let's write the code... open hiew and go to offset 2A0h (that'll become 4002A0h as soon as the file gets mapped and the imagebase gets added), and inject our hooking routine:

        push    eax                           ; save EAX
        mov     eax, [esp+4]            ; return VA in EAX
        mov     [4002E3h], eax        ; we save it in a variable X
        pop     eax                           ; restore EAX
        add     esp, 4                        ; [ESP] points to the SYSTEMTIME structure
        call    dword [4002DDh]      ; == call GetLocalTime (dword patched from the Mem Patcher)
        mov     [4002E9h], eax         ; save EAX in a variable Y
        mov     eax, [esp-4]              ; EAX holds a pointer to the structure
        mov     word [eax], 07CFh   ; WORD wYear
        mov     word [eax+2], 07h    ; WORD wMonth
        mov     word [eax+6], 012h  ; WORD wDay
        mov     eax, [4002E9h]         ; restore EAX from variable Y
        jmp     dword [4002E3h]      ; back to .text via the variable X

gone :)

for those among you not very familiar with Hiew and its barbarian way of handling byte, word and dword ptr, you must know that they are respectively B,[blabla]   ,   W,[blabla]   and   D,[blabla].

once u did this, you can run our mempatcher, and everything will work perfectly... your Conseal PC firewall will never expire again, and we made something unusual for sure... i had some fun, what about u ?? ;)

 

Part 3: Shout Outz


Greetings logorrhea shortened by reverser+, maybe not enough :-)

For any question, comment, add-on, polemic etc etc my email is neural@cryogen.com

my nickname on IRC ~ #cracking4newbies (EFNet) or #crack-it (IRCNet) ~ is nuural_en.

other stuff written by me can be found at http://neudump.cjb.net

my preferred italian reverse engineering group's page is at http://ringzer0.cjb.net

and my preferred international reversing group's page is http://dread99.cjb.net

 

'till next time,

NeuRaL_NoiSE 1999 for RingZ3r0 and DREAD.

 

Ob Duh

I wont even bother explaining you that you should BUY programs if you intend to use them for a longer period than the allowed one. Should you want to STEAL software instead (unlikely in this case :-) you don't need to crack protection schemes at all: you'll find everything on most Warez sites, complete and already regged, farewell, don't come back.

You are deep inside reverser's page of reverse engineering, choose your way out:


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