joana&pedro: Emulating Shellcodes

Lets check different Cobalt Strike shellcodes and stages in the shellcodes emulator SCEMU.

This stages are fully emulated well and can get the IOC and the behavior of the shellcode.

But lets see another first stage big shellcode with c runtime embedded in a second stage.

In this case is loading tons of API using GetProcAddress at the beginning, then some encode/decode pointer and tls get/set values to store an address. And ends up crashing because is jumping an address that seems more code than address 0x9090f1eb.

Here there are two types of allocations:

Lets spawn a console on -c 3307548 and see if some of this allocations has the next stage.

The "m" command show all the memory maps but the "ma" show only the allocations done by the shellcode.

Dumping memory with "md" we see that there is data, and dissasembling this address with "d" we see the prolog of a function.

So we have second stage unpacked in alloc_e40064

With "mdd" we do a memory dump to disk we found the size in previous screenshot, and we can do some static reversing of stage2 in radare/ghidra/ida

In radare we can verify that the extracted is the next stage:

I usually do correlation between the emulation and ghidra, to understand the algorithms.

If wee look further we can realize that the emulator called a function on the stage2, we can see the change of code base address and is calling the allocated buffer in 0x4f...

And this stage2 perform several API calls let's check it in ghidra.

We can see in the emulator that enters in the IF block, and what are the (*DAT_...)() calls

Before a crash lets continue to the SEH pointer, in this case is the way, and the exception routine checks IsDebuggerPresent() which is not any debugger pressent for sure, so eax = 0;

So lets say yes and continue the emulation.

Both IsDebuggerPresent() and UnHandledExceptionFilter() can be used to detect a debugger, but the emulator return what has to return to not be detected.

Nevertheless the shellcode detects something and terminates the process.

Lets trace the branches to understand the logic:

target/release/scemu -f shellcodes/unsuported_cs.bin -vv | egrep '(\*\*|j|cmp|test)'

Continuing the emulation it's setting the SEH pointer to previous stage:

Lets see from the console where is pointing the SEH chain item:

to be continued ...

https://github.com/sha0coder/scemu

Quando eu te falei em amor

Quando os meus olhos te tocaram
Eu senti que encontrara
A outra, metade de mim
Tive medo de acordar
Como se vivesse um sonho
Que não pensei em realizar
E a força do desejo
Faz me chegar perto de ti

Quando eu te falei em amor
Tu sorriste para mim
E o mundo ficou bem melhor
Quando eu te falei em amor
Nos sentimos os dois
Que o amanha vem depois
E não no fim

Estas linhas que hoje escrevo
São do livro da memória
Do que eu sinto por ti
E tudo o que tu me das
É parte da história que eu ainda não vivi
E a força do desejo
Faz me chegar de ti

Quando eu te falei em amor
Tu sorriste para mim
E o mundo ficou bem melhor
Quando eu te falei em amor
Nos sentimos os dois
Que o amanha vem depois e não no fim

André Sardet

Collide

The dawn is breaking
A light shining through
You're barely waking
And I'm tangled up in you
Yeah

But I'm open, you're closed
Where I follow, you'll go
I worry I won't see your face
Light up again

Even the best fall down sometimes
Even the wrong words seem to rhyme
Out of the doubt that fills my mind
I somehow find, you and I collide

I'm quiet, you know
You make a first impression
I've found I'm scared to know
I'm always on your mind

Even the best fall down sometimes
Even the stars refuse to shine
Out of the back you fall in time
I somehow find, you and I collide

Don't stop here
I've lost my place
I'm close behind

Even the best fall down sometimes
Even the wrong words seem to rhyme
Out of the doubt that fills your mind

You finally find, you and I collide
You finally find You and I collide
You finally findYou and I collide
Howie Day

Everything

You're a falling star, You're the get away
car.
You're the line in the sand when I go too
far.
You're the swimming pool, on an August day.
And You're the perfect thing to see.

And you play it coy, but it's kinda cute.
Ah, When you smile at me you know exactly what you
do.
Baby don't pretend, that you don't know it's
true.
Cause you can see it when I look at you.

And in this crazy life, and through these crazy
times
It's you, it's you, You make me sing.
You're every line, you're every word, you're
everything.

You're a carousel, you're a wishing well,
And you light me up, when you ring my bell.
You're a mystery, you're from outer space,
You're every minute of my everyday.

And I can't believe, uh that I'm your man,
And I get to kiss you baby just because I
can.
Whatever comes our way, ah we'll see it
through,
And you know that's what our love can do.

And in this crazy life, and through these crazy
times
It's you, it's you, You make me sing
You're every line, you're every word, you're
everything.

So, La, La, La, La, La, La, La
So, La, La, La, La, La, La, La

And in this crazy life, and through these crazy
times
It's you, it's you, You make me sing.
You're every line, you're every word, you're
everything.
You're every song, and I sing along.
Cause you're my everything.
yeah, yeah

So, La, La, La, La, La, La, La
So, La, La, La, La, La, La, La

Michael Bublé