Actor(s): Turla
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rule win_crutch_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-07-11" version = "1" description = "Detects win.crutch." 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.crutch" malpedia_rule_date = "20230705" malpedia_hash = "42d0574f4405bd7d2b154d321d345acb18834a41" malpedia_version = "20230715" 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 = { 7477 8b5c2420 8b0b 83b9a403000000 7446 8b4560 85c0 } // n = 7, score = 100 // 7477 | je 0x79 // 8b5c2420 | mov ebx, dword ptr [esp + 0x20] // 8b0b | mov ecx, dword ptr [ebx] // 83b9a403000000 | cmp dword ptr [ecx + 0x3a4], 0 // 7446 | je 0x48 // 8b4560 | mov eax, dword ptr [ebp + 0x60] // 85c0 | test eax, eax $sequence_1 = { c6442e0100 e8???????? 8b54244c 8b442448 8b4c243c 52 50 } // n = 7, score = 100 // c6442e0100 | mov byte ptr [esi + ebp + 1], 0 // e8???????? | // 8b54244c | mov edx, dword ptr [esp + 0x4c] // 8b442448 | mov eax, dword ptr [esp + 0x48] // 8b4c243c | mov ecx, dword ptr [esp + 0x3c] // 52 | push edx // 50 | push eax $sequence_2 = { 5e 8bc3 5b e9???????? 8b742418 85f6 7477 } // n = 7, score = 100 // 5e | pop esi // 8bc3 | mov eax, ebx // 5b | pop ebx // e9???????? | // 8b742418 | mov esi, dword ptr [esp + 0x18] // 85f6 | test esi, esi // 7477 | je 0x79 $sequence_3 = { 51 50 e8???????? 8b542424 83c40c 3bd3 0f8435feffff } // n = 7, score = 100 // 51 | push ecx // 50 | push eax // e8???????? | // 8b542424 | mov edx, dword ptr [esp + 0x24] // 83c40c | add esp, 0xc // 3bd3 | cmp edx, ebx // 0f8435feffff | je 0xfffffe3b $sequence_4 = { e8???????? 83c404 8be8 eb1b 55 ff15???????? 8b442410 } // n = 7, score = 100 // e8???????? | // 83c404 | add esp, 4 // 8be8 | mov ebp, eax // eb1b | jmp 0x1d // 55 | push ebp // ff15???????? | // 8b442410 | mov eax, dword ptr [esp + 0x10] $sequence_5 = { 8bec 56 8b7508 833cf5906e071000 7513 56 e8???????? } // n = 7, score = 100 // 8bec | mov ebp, esp // 56 | push esi // 8b7508 | mov esi, dword ptr [ebp + 8] // 833cf5906e071000 | cmp dword ptr [esi*8 + 0x10076e90], 0 // 7513 | jne 0x15 // 56 | push esi // e8???????? | $sequence_6 = { ffd0 83c404 83ceff 895c245c 899dc04a0000 895d08 83feff } // n = 7, score = 100 // ffd0 | call eax // 83c404 | add esp, 4 // 83ceff | or esi, 0xffffffff // 895c245c | mov dword ptr [esp + 0x5c], ebx // 899dc04a0000 | mov dword ptr [ebp + 0x4ac0], ebx // 895d08 | mov dword ptr [ebp + 8], ebx // 83feff | cmp esi, -1 $sequence_7 = { 33ff 3bc7 7422 50 ff15???????? 83c404 89bed0010000 } // n = 7, score = 100 // 33ff | xor edi, edi // 3bc7 | cmp eax, edi // 7422 | je 0x24 // 50 | push eax // ff15???????? | // 83c404 | add esp, 4 // 89bed0010000 | mov dword ptr [esi + 0x1d0], edi $sequence_8 = { 8d442434 50 8d4c2468 51 57 e8???????? 83c428 } // n = 7, score = 100 // 8d442434 | lea eax, [esp + 0x34] // 50 | push eax // 8d4c2468 | lea ecx, [esp + 0x68] // 51 | push ecx // 57 | push edi // e8???????? | // 83c428 | add esp, 0x28 $sequence_9 = { 837d4010 c745280f000000 c7452400000000 c6451400 720b ff752c e8???????? } // n = 7, score = 100 // 837d4010 | cmp dword ptr [ebp + 0x40], 0x10 // c745280f000000 | mov dword ptr [ebp + 0x28], 0xf // c7452400000000 | mov dword ptr [ebp + 0x24], 0 // c6451400 | mov byte ptr [ebp + 0x14], 0 // 720b | jb 0xd // ff752c | push dword ptr [ebp + 0x2c] // e8???????? | condition: 7 of them and filesize < 1067008 }
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