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rule win_nokoyawa_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-03-28" version = "1" description = "Detects win.nokoyawa." 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.nokoyawa" malpedia_rule_date = "20230328" malpedia_hash = "9d2d75cef573c1c2d861f5197df8f563b05a305d" malpedia_version = "20230407" 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 = { c1e908 81e100ff0000 0bc1 488b4c2440 8b4910 c1e918 } // n = 6, score = 100 // c1e908 | mov eax, dword ptr [eax + 8] // 81e100ff0000 | dec eax // 0bc1 | mov dword ptr [esp + 0x40], eax // 488b4c2440 | dec eax // 8b4910 | mov eax, dword ptr [esp + 0x30] // c1e918 | dec eax $sequence_1 = { b804000000 486bc001 488b8c24c0010000 8b440114 ffc0 b904000000 486bc901 } // n = 7, score = 100 // b804000000 | movzx eax, word ptr [eax] // 486bc001 | test eax, eax // 488b8c24c0010000 | jne 0x5d // 8b440114 | dec eax // ffc0 | mov eax, dword ptr [esp + 0x30] // b904000000 | dec eax // 486bc901 | mov eax, dword ptr [esp + 8] $sequence_2 = { 4889542410 48894c2408 4883ec28 488b442430 8b00 488b4c2448 } // n = 6, score = 100 // 4889542410 | mov edx, 0xca62c1d6 // 48894c2408 | mov ecx, edx // 4883ec28 | mov edx, dword ptr [esp + 0x160] // 488b442430 | add edx, ecx // 8b00 | mov ecx, edx // 488b4c2448 | mov edx, 0xca62c1d6 $sequence_3 = { c1e91b 8b54240c c1e205 0bd1 8bca 8b942410010000 03d1 } // n = 7, score = 100 // c1e91b | movzx ecx, byte ptr [esp + 0x38] // 8b54240c | mov byte ptr [eax], cl // c1e205 | dec eax // 0bd1 | mov eax, dword ptr [esp + 0x10] // 8bca | dec eax // 8b942410010000 | sub ecx, eax // 03d1 | dec eax $sequence_4 = { 48ffc0 4889442410 488b442440 48ffc8 4889442440 ebd0 488b442430 } // n = 7, score = 100 // 48ffc0 | lea eax, [eax + ecx + 0x6ed9eba1] // 4889442410 | mov ecx, dword ptr [esp + 4] // 488b442440 | add ecx, eax // 48ffc8 | mov edx, dword ptr [esp + 0xa0] // 4889442440 | add edx, ecx // ebd0 | mov ecx, edx // 488b442430 | lea eax, [eax + ecx + 0x6ed9eba1] $sequence_5 = { 4881ecb8020000 8b05???????? 89442424 b9e8030000 ff15???????? 33d2 488d0dab7d0000 } // n = 7, score = 100 // 4881ecb8020000 | mov eax, 4 // 8b05???????? | // 89442424 | dec eax // b9e8030000 | imul eax, eax, 7 // ff15???????? | // 33d2 | mov ecx, 4 // 488d0dab7d0000 | dec eax $sequence_6 = { 482b442430 4889442438 488b442438 4889442428 488b442470 488b4c2430 } // n = 6, score = 100 // 482b442430 | dec eax // 4889442438 | mov eax, dword ptr [esp + 0x70] // 488b442438 | dec eax // 4889442428 | mov ecx, dword ptr [esp + 0x20] // 488b442470 | dec eax // 488b4c2430 | lea eax, [eax + ecx + 0x20] $sequence_7 = { 488bc8 e8???????? 488d0dd9740000 e8???????? 4898 } // n = 5, score = 100 // 488bc8 | xor eax, eax // e8???????? | // 488d0dd9740000 | test eax, eax // e8???????? | // 4898 | jne 0x105f $sequence_8 = { 8b09 33c8 8bc1 488b4c2438 8901 488b442438 8b00 } // n = 7, score = 100 // 8b09 | lea ecx, [esp + 0x5c] // 33c8 | dec eax // 8bc1 | cwde // 488b4c2438 | inc ecx // 8901 | mov eax, 0x40 // 488b442438 | mov edx, 0x36 // 8b00 | dec eax $sequence_9 = { c1e205 0bd1 8bca 8b942490000000 03d1 } // n = 5, score = 100 // c1e205 | dec eax // 0bd1 | lea ecx, [esp + 0x90] // 8bca | dec eax // 8b942490000000 | lea eax, [esp + 0x38] // 03d1 | dec eax condition: 7 of them and filesize < 92160 }
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