YARA Detection Rule: CobaltStrike_Resources_Httpsstager_Bin_v2_5_through_v4_x
Repository: Neo23x0/signature-base
Detects: Cobalt Strike's resources/httpsstager.bin signature for versions 2.5 to 4.x
Author: gssincla@google.com
Reference: https://cloud.google.com/blog/products/identity-security/making-cobalt-strike-harder-for-threat-actors-to-abuse

Pattern signatures:
/*
		31 ??     xor     eax, eax
		AC        lodsb
		C1 ?? 0D  ror     edi, 0Dh
		01 ??     add     edi, eax
		38 ??     cmp     al, ah
		75 ??     jnz     short loc_10000054
		03 [2]    add     edi, [ebp-8]
		3B [2]    cmp     edi, [ebp+24h]
		75 ??     jnz     short loc_1000004A
		5?        pop     eax
		8B ?? 24  mov     ebx, [eax+24h]
		01 ??     add     ebx, edx
		66 8B [2] mov     cx, [ebx+ecx*2]
		8B ?? 1C  mov     ebx, [eax+1Ch]
		01 ??     add     ebx, edx
		8B ?? 8B  mov     eax, [ebx+ecx*4]
		01 ??     add     eax, edx
		89 [3]    mov     [esp+28h+var_4], eax
		5?        pop     ebx
		5?        pop     ebx
	*/

	$apiLocator = {
			31 ?? 
			AC
			C1 ?? 0D 
			01 ?? 
			38 ?? 
			75 ?? 
			03 [2]
			3B [2]
			75 ?? 
			5? 
			8B ?? 24 
			01 ?? 
			66 8B [2]
			8B ?? 1C 
			01 ?? 
			8B ?? 8B 
			01 ?? 
			89 [3]
			5? 
			5? 
		}

  // the signature for httpstager and httpsstager really only differ by the flags passed to WinInet API
  // and the inclusion of the InternetSetOp

Detection condition:
$apiLocator and $InternetSetOptionA

Full rule:
rule CobaltStrike_Resources_Httpsstager_Bin_v2_5_through_v4_x
{
	meta:
		description = "Cobalt Strike's resources/httpsstager.bin signature for versions 2.5 to 4.x"
		hash =  "5ebe813a4c899b037ac0ee0962a439833964a7459b7a70f275ac73ea475705b3"
		author = "gssincla@google.com"
		reference = "https://cloud.google.com/blog/products/identity-security/making-cobalt-strike-harder-for-threat-actors-to-abuse"
		date = "2022-11-18"
		
		id = "f45aa40a-3936-50f9-a60e-de7181862d19"
	strings:
	/*
		31 ??     xor     eax, eax
		AC        lodsb
		C1 ?? 0D  ror     edi, 0Dh
		01 ??     add     edi, eax
		38 ??     cmp     al, ah
		75 ??     jnz     short loc_10000054
		03 [2]    add     edi, [ebp-8]
		3B [2]    cmp     edi, [ebp+24h]
		75 ??     jnz     short loc_1000004A
		5?        pop     eax
		8B ?? 24  mov     ebx, [eax+24h]
		01 ??     add     ebx, edx
		66 8B [2] mov     cx, [ebx+ecx*2]
		8B ?? 1C  mov     ebx, [eax+1Ch]
		01 ??     add     ebx, edx
		8B ?? 8B  mov     eax, [ebx+ecx*4]
		01 ??     add     eax, edx
		89 [3]    mov     [esp+28h+var_4], eax
		5?        pop     ebx
		5?        pop     ebx
	*/

	$apiLocator = {
			31 ?? 
			AC
			C1 ?? 0D 
			01 ?? 
			38 ?? 
			75 ?? 
			03 [2]
			3B [2]
			75 ?? 
			5? 
			8B ?? 24 
			01 ?? 
			66 8B [2]
			8B ?? 1C 
			01 ?? 
			8B ?? 8B 
			01 ?? 
			89 [3]
			5? 
			5? 
		}

  // the signature for httpstager and httpsstager really only differ by the flags passed to WinInet API
  // and the inclusion of the InternetSetOptionA call. We will trigger off that API
	/*
		6A 04          push    4
		5?             push    eax
		6A 1F          push    1Fh
		5?             push    esi
		68 75 46 9E 86 push    InternetSetOptionA
		FF ??          call    ebp
	*/

	$InternetSetOptionA = {
			6A 04
			5? 
			6A 1F
			5? 
			68 75 46 9E 86
			FF  
		}
	
	condition:
		$apiLocator and $InternetSetOptionA
}