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rule win_virut_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-07-11" version = "1" description = "Detects win.virut." 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.virut" 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 = { 50 ff15???????? 8bf0 3bf3 0f8e82000000 ff74240c 57 } // n = 7, score = 200 // 50 | push eax // ff15???????? | // 8bf0 | mov esi, eax // 3bf3 | cmp esi, ebx // 0f8e82000000 | jle 0x88 // ff74240c | push dword ptr [esp + 0xc] // 57 | push edi $sequence_1 = { 50 54 50 56 51 } // n = 5, score = 200 // 50 | push eax // 54 | push esp // 50 | push eax // 56 | push esi // 51 | push ecx $sequence_2 = { 6a10 59 f3ab 50 50 50 } // n = 6, score = 200 // 6a10 | push 0x10 // 59 | pop ecx // f3ab | rep stosd dword ptr es:[edi], eax // 50 | push eax // 50 | push eax // 50 | push eax $sequence_3 = { 57 56 ff15???????? 56 ff15???????? 6a44 } // n = 6, score = 200 // 57 | push edi // 56 | push esi // ff15???????? | // 56 | push esi // ff15???????? | // 6a44 | push 0x44 $sequence_4 = { 8bcf 52 f6d9 52 83e103 } // n = 5, score = 200 // 8bcf | mov ecx, edi // 52 | push edx // f6d9 | neg cl // 52 | push edx // 83e103 | and ecx, 3 $sequence_5 = { 69c06d4ec641 0539300000 a3???????? c1e80a c3 55 8bec } // n = 7, score = 200 // 69c06d4ec641 | imul eax, eax, 0x41c64e6d // 0539300000 | add eax, 0x3039 // a3???????? | // c1e80a | shr eax, 0xa // c3 | ret // 55 | push ebp // 8bec | mov ebp, esp $sequence_6 = { 7416 e314 50 8bd4 6a00 } // n = 5, score = 200 // 7416 | je 0x18 // e314 | jecxz 0x16 // 50 | push eax // 8bd4 | mov edx, esp // 6a00 | push 0 $sequence_7 = { 50 53 6a05 8bcc } // n = 4, score = 200 // 50 | push eax // 53 | push ebx // 6a05 | push 5 // 8bcc | mov ecx, esp $sequence_8 = { 74c7 885c2413 ff742418 ff15???????? 385c2413 0f8402010000 803f4d } // n = 7, score = 200 // 74c7 | je 0xffffffc9 // 885c2413 | mov byte ptr [esp + 0x13], bl // ff742418 | push dword ptr [esp + 0x18] // ff15???????? | // 385c2413 | cmp byte ptr [esp + 0x13], bl // 0f8402010000 | je 0x108 // 803f4d | cmp byte ptr [edi], 0x4d $sequence_9 = { 2bcb 60 8bcb f3a6 61 } // n = 5, score = 200 // 2bcb | sub ecx, ebx // 60 | pushal // 8bcb | mov ecx, ebx // f3a6 | repe cmpsb byte ptr [esi], byte ptr es:[edi] // 61 | popal $sequence_10 = { 50 ff15???????? 6800100000 8d842474050000 50 8d8424d0000000 50 } // n = 7, score = 200 // 50 | push eax // ff15???????? | // 6800100000 | push 0x1000 // 8d842474050000 | lea eax, [esp + 0x574] // 50 | push eax // 8d8424d0000000 | lea eax, [esp + 0xd0] // 50 | push eax $sequence_11 = { 885c2422 885c2423 33c9 e8???????? } // n = 4, score = 200 // 885c2422 | mov byte ptr [esp + 0x22], bl // 885c2423 | mov byte ptr [esp + 0x23], bl // 33c9 | xor ecx, ecx // e8???????? | $sequence_12 = { 46 3bf1 7ce5 8b442414 6a03 99 } // n = 6, score = 200 // 46 | inc esi // 3bf1 | cmp esi, ecx // 7ce5 | jl 0xffffffe7 // 8b442414 | mov eax, dword ptr [esp + 0x14] // 6a03 | push 3 // 99 | cdq $sequence_13 = { 8d8424d4010000 50 56 e8???????? 83c40c } // n = 5, score = 200 // 8d8424d4010000 | lea eax, [esp + 0x1d4] // 50 | push eax // 56 | push esi // e8???????? | // 83c40c | add esp, 0xc $sequence_14 = { 8bc4 6a00 6800000008 6a40 51 52 } // n = 6, score = 200 // 8bc4 | mov eax, esp // 6a00 | push 0 // 6800000008 | push 0x8000000 // 6a40 | push 0x40 // 51 | push ecx // 52 | push edx $sequence_15 = { 43 4b 3332 2e44 4c } // n = 5, score = 200 // 43 | inc ebx // 4b | dec ebx // 3332 | xor esi, dword ptr [edx] // 2e44 | inc esp // 4c | dec esp condition: 7 of them and filesize < 98304 }
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