Actor(s): Lazarus Group
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rule win_bistromath_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2022-05-16" version = "1" description = "Detects win.bistromath." info = "autogenerated rule brought to you by yara-signator" tool = "yara-signator v0.6.0" signator_config = "callsandjumps;datarefs;binvalue" malpedia_reference = "https://malpedia.caad.fkie.fraunhofer.de/details/win.bistromath" malpedia_rule_date = "20220513" malpedia_hash = "7f4b2229e6ae614d86d74917f6d5b41890e62a26" malpedia_version = "20220516" malpedia_license = "CC BY-SA 4.0" malpedia_sharing = "TLP:WHITE" /* DISCLAIMER * The strings used in this rule have been automatically selected from the * disassembly of memory dumps and unpacked files, using YARA-Signator. * The code and documentation is published here: * https://github.com/fxb-cocacoding/yara-signator * As Malpedia is used as data source, please note that for a given * number of families, only single samples are documented. * This likely impacts the degree of generalization these rules will offer. * Take the described generation method also into consideration when you * apply the rules in your use cases and assign them confidence levels. */ strings: $sequence_0 = { 8b5510 8955f4 85d2 753d 52 8bcb e8???????? } // n = 7, score = 400 // 8b5510 | mov edx, dword ptr [ebp + 0x10] // 8955f4 | mov dword ptr [ebp - 0xc], edx // 85d2 | test edx, edx // 753d | jne 0x3f // 52 | push edx // 8bcb | mov ecx, ebx // e8???????? | $sequence_1 = { c684242b02000065 c684242c02000073 c684242d02000073 c684242e02000000 48 8d942420020000 48 } // n = 7, score = 400 // c684242b02000065 | mov byte ptr [esp + 0x22b], 0x65 // c684242c02000073 | mov byte ptr [esp + 0x22c], 0x73 // c684242d02000073 | mov byte ptr [esp + 0x22d], 0x73 // c684242e02000000 | mov byte ptr [esp + 0x22e], 0 // 48 | dec eax // 8d942420020000 | lea edx, [esp + 0x220] // 48 | dec eax $sequence_2 = { 8b742410 f6462c10 0f858a000000 837c247000 0f857f000000 8b442464 3b442454 } // n = 7, score = 400 // 8b742410 | mov esi, dword ptr [esp + 0x10] // f6462c10 | test byte ptr [esi + 0x2c], 0x10 // 0f858a000000 | jne 0x90 // 837c247000 | cmp dword ptr [esp + 0x70], 0 // 0f857f000000 | jne 0x85 // 8b442464 | mov eax, dword ptr [esp + 0x64] // 3b442454 | cmp eax, dword ptr [esp + 0x54] $sequence_3 = { 7472 98 8b8c8688000000 85c9 7408 8b4944 e8???????? } // n = 7, score = 400 // 7472 | je 0x74 // 98 | cwde // 8b8c8688000000 | mov ecx, dword ptr [esi + eax*4 + 0x88] // 85c9 | test ecx, ecx // 7408 | je 0xa // 8b4944 | mov ecx, dword ptr [ecx + 0x44] // e8???????? | $sequence_4 = { 7de1 eb07 83caff 89542414 83f96c 7523 0fbe4e01 } // n = 7, score = 400 // 7de1 | jge 0xffffffe3 // eb07 | jmp 9 // 83caff | or edx, 0xffffffff // 89542414 | mov dword ptr [esp + 0x14], edx // 83f96c | cmp ecx, 0x6c // 7523 | jne 0x25 // 0fbe4e01 | movsx ecx, byte ptr [esi + 1] $sequence_5 = { c6434001 8bd6 ff4744 8bcb c7470c07000000 e8???????? 5f } // n = 7, score = 400 // c6434001 | mov byte ptr [ebx + 0x40], 1 // 8bd6 | mov edx, esi // ff4744 | inc dword ptr [edi + 0x44] // 8bcb | mov ecx, ebx // c7470c07000000 | mov dword ptr [edi + 0xc], 7 // e8???????? | // 5f | pop edi $sequence_6 = { 8b7de0 8b45fc 33d2 f775d8 8b45f4 eb02 33d2 } // n = 7, score = 400 // 8b7de0 | mov edi, dword ptr [ebp - 0x20] // 8b45fc | mov eax, dword ptr [ebp - 4] // 33d2 | xor edx, edx // f775d8 | div dword ptr [ebp - 0x28] // 8b45f4 | mov eax, dword ptr [ebp - 0xc] // eb02 | jmp 4 // 33d2 | xor edx, edx $sequence_7 = { 807e0802 0f8587000000 8b5e04 e8???????? ff7508 8b0b 8bd7 } // n = 7, score = 400 // 807e0802 | cmp byte ptr [esi + 8], 2 // 0f8587000000 | jne 0x8d // 8b5e04 | mov ebx, dword ptr [esi + 4] // e8???????? | // ff7508 | push dword ptr [ebp + 8] // 8b0b | mov ecx, dword ptr [ebx] // 8bd7 | mov edx, edi $sequence_8 = { 8be5 5d c3 6aff 6a01 6aff 8d4e08 } // n = 7, score = 400 // 8be5 | mov esp, ebp // 5d | pop ebp // c3 | ret // 6aff | push -1 // 6a01 | push 1 // 6aff | push -1 // 8d4e08 | lea ecx, [esi + 8] $sequence_9 = { 7530 8b4d0c e8???????? 85c0 7420 8b442410 f6402c20 } // n = 7, score = 400 // 7530 | jne 0x32 // 8b4d0c | mov ecx, dword ptr [ebp + 0xc] // e8???????? | // 85c0 | test eax, eax // 7420 | je 0x22 // 8b442410 | mov eax, dword ptr [esp + 0x10] // f6402c20 | test byte ptr [eax + 0x2c], 0x20 condition: 7 of them and filesize < 33816576 }
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