YARA Detection Rule: CobaltStrike_Sleeve_BeaconLoader_VA_x86_o_v4_3_v4_4_v4_5_and_v4_6
Repository: Neo23x0/signature-base
Detects: Cobalt Strike's sleeve/BeaconLoader.VA.x86.o (VirtualAlloc) Versions 4.3 through at least 4.6
Author: gssincla@google.com
Reference: https://cloud.google.com/blog/products/identity-security/making-cobalt-strike-harder-for-threat-actors-to-abuse

Pattern signatures:
/*
      C6 45 B0 56 mov     [ebp+var_50], 56h ; 'V'
      C6 45 B1 69 mov     [ebp+var_50+1], 69h ; 'i'
      C6 45 B2 72 mov     [ebp+var_50+2], 72h ; 'r'
      C6 45 B3 74 mov     [ebp+var_50+3], 74h ; 't'
      C6 45 B4 75 mov     [ebp+var_50+4], 75h ; 'u'
      C6 45 B5 61 mov     [ebp+var_50+5], 61h ; 'a'
      C6 45 B6 6C mov     [ebp+var_50+6], 6Ch ; 'l'
      C6 45 B7 41 mov     [ebp+var_50+7], 41h ; 'A'
      C6 45 B8 6C mov     [ebp+var_50+8], 6Ch ; 'l'
      C6 45 B9 6C mov     [ebp+var_50+9], 6Ch ; 'l'
      C6 45 BA 6F mov     [ebp+var_50+0Ah], 6Fh ; 'o'
      C6 45 BB 63 mov     [ebp+var_50+0Bh], 63h ; 'c'
      C6 45 BC 00 mov     [ebp+var_50+0Ch], 0
    */

    $core_sig = {
      C6 45 B0 56
      C6 45 B1 69
      C6 45 B2 72
      C6 45 B3 74
      C6 45 B4 75
      C6 45 B5 61
      C6 45 B6 6C
      C6 45 B7 41
      C6 45 B8 6C
      C6 45 B9 6C
      C6 45 BA 6F
      C6 45 BB 63
      C6 45 BC 00
    }

    /*
      8B 4D FC    mov     ecx, [ebp+var_4]
      83

Detection condition:
all of them

Full rule:
rule CobaltStrike_Sleeve_BeaconLoader_VA_x86_o_v4_3_v4_4_v4_5_and_v4_6
{
  meta:
    description = "Cobalt Strike's sleeve/BeaconLoader.VA.x86.o (VirtualAlloc) Versions 4.3 through at least 4.6"
    hash =  "94d1b993a9d5786e0a9b44ea1c0dc27e225c9eb[PII_REDACTED]715c47f9af78cc1"
		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 = "5f89c4be-f4c5-54d3-b923-d125de53902f"
  strings:
    /*
      C6 45 B0 56 mov     [ebp+var_50], 56h ; 'V'
      C6 45 B1 69 mov     [ebp+var_50+1], 69h ; 'i'
      C6 45 B2 72 mov     [ebp+var_50+2], 72h ; 'r'
      C6 45 B3 74 mov     [ebp+var_50+3], 74h ; 't'
      C6 45 B4 75 mov     [ebp+var_50+4], 75h ; 'u'
      C6 45 B5 61 mov     [ebp+var_50+5], 61h ; 'a'
      C6 45 B6 6C mov     [ebp+var_50+6], 6Ch ; 'l'
      C6 45 B7 41 mov     [ebp+var_50+7], 41h ; 'A'
      C6 45 B8 6C mov     [ebp+var_50+8], 6Ch ; 'l'
      C6 45 B9 6C mov     [ebp+var_50+9], 6Ch ; 'l'
      C6 45 BA 6F mov     [ebp+var_50+0Ah], 6Fh ; 'o'
      C6 45 BB 63 mov     [ebp+var_50+0Bh], 63h ; 'c'
      C6 45 BC 00 mov     [ebp+var_50+0Ch], 0
    */

    $core_sig = {
      C6 45 B0 56
      C6 45 B1 69
      C6 45 B2 72
      C6 45 B3 74
      C6 45 B4 75
      C6 45 B5 61
      C6 45 B6 6C
      C6 45 B7 41
      C6 45 B8 6C
      C6 45 B9 6C
      C6 45 BA 6F
      C6 45 BB 63
      C6 45 BC 00
    }

    /*
      8B 4D FC    mov     ecx, [ebp+var_4]
      83 C1 01    add     ecx, 1
      89 4D FC    mov     [ebp+var_4], ecx
      8B 55 FC    mov     edx, [ebp+var_4]
      3B 55 0C    cmp     edx, [ebp+arg_4]
      73 19       jnb     short loc_231
      0F B6 45 10 movzx   eax, [ebp+arg_8]
      8B 4D 08    mov     ecx, [ebp+arg_0]
      03 4D FC    add     ecx, [ebp+var_4]
      0F BE 11    movsx   edx, byte ptr [ecx]
      33 D0       xor     edx, eax
      8B 45 08    mov     eax, [ebp+arg_0]
      03 45 FC    add     ea