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rule win_downeks_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-03-28" version = "1" description = "Detects win.downeks." 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.downeks" 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 = { e8???????? 8b7708 83fe01 7dad 8b4dfc 5e 33cd } // n = 7, score = 200 // e8???????? | // 8b7708 | mov esi, dword ptr [edi + 8] // 83fe01 | cmp esi, 1 // 7dad | jge 0xffffffaf // 8b4dfc | mov ecx, dword ptr [ebp - 4] // 5e | pop esi // 33cd | xor ecx, ebp $sequence_1 = { 85c0 0f98c1 8bc1 85c0 74bd 8b4b60 8b15???????? } // n = 7, score = 200 // 85c0 | test eax, eax // 0f98c1 | sets cl // 8bc1 | mov eax, ecx // 85c0 | test eax, eax // 74bd | je 0xffffffbf // 8b4b60 | mov ecx, dword ptr [ebx + 0x60] // 8b15???????? | $sequence_2 = { e8???????? 8bf0 83c40c 85f6 752d 8d4612 eb21 } // n = 7, score = 200 // e8???????? | // 8bf0 | mov esi, eax // 83c40c | add esp, 0xc // 85f6 | test esi, esi // 752d | jne 0x2f // 8d4612 | lea eax, [esi + 0x12] // eb21 | jmp 0x23 $sequence_3 = { 6a01 6a00 56 50 ff15???????? 8b8da8fdffff 51 } // n = 7, score = 200 // 6a01 | push 1 // 6a00 | push 0 // 56 | push esi // 50 | push eax // ff15???????? | // 8b8da8fdffff | mov ecx, dword ptr [ebp - 0x258] // 51 | push ecx $sequence_4 = { e8???????? 85db 0f8ead000000 8b955cffffff 8bbd58ffffff 8d4bff 2bd7 } // n = 7, score = 200 // e8???????? | // 85db | test ebx, ebx // 0f8ead000000 | jle 0xb3 // 8b955cffffff | mov edx, dword ptr [ebp - 0xa4] // 8bbd58ffffff | mov edi, dword ptr [ebp - 0xa8] // 8d4bff | lea ecx, [ebx - 1] // 2bd7 | sub edx, edi $sequence_5 = { 85f6 7508 b81b000000 5e 5d c3 8d5001 } // n = 7, score = 200 // 85f6 | test esi, esi // 7508 | jne 0xa // b81b000000 | mov eax, 0x1b // 5e | pop esi // 5d | pop ebp // c3 | ret // 8d5001 | lea edx, [eax + 1] $sequence_6 = { 8bc1 83f82c 7435 83f85d 745a 837f1800 7417 } // n = 7, score = 200 // 8bc1 | mov eax, ecx // 83f82c | cmp eax, 0x2c // 7435 | je 0x37 // 83f85d | cmp eax, 0x5d // 745a | je 0x5c // 837f1800 | cmp dword ptr [edi + 0x18], 0 // 7417 | je 0x19 $sequence_7 = { e8???????? 50 8b852cffffff 56 6854150804 50 e8???????? } // n = 7, score = 200 // e8???????? | // 50 | push eax // 8b852cffffff | mov eax, dword ptr [ebp - 0xd4] // 56 | push esi // 6854150804 | push 0x4081554 // 50 | push eax // e8???????? | $sequence_8 = { b927000000 8db588fdffff 50 f3a5 e8???????? 83c404 8bfc } // n = 7, score = 200 // b927000000 | mov ecx, 0x27 // 8db588fdffff | lea esi, [ebp - 0x278] // 50 | push eax // f3a5 | rep movsd dword ptr es:[edi], dword ptr [esi] // e8???????? | // 83c404 | add esp, 4 // 8bfc | mov edi, esp $sequence_9 = { c1e91f 33ff 03ca 7435 33db 8d55c0 52 } // n = 7, score = 200 // c1e91f | shr ecx, 0x1f // 33ff | xor edi, edi // 03ca | add ecx, edx // 7435 | je 0x37 // 33db | xor ebx, ebx // 8d55c0 | lea edx, [ebp - 0x40] // 52 | push edx condition: 7 of them and filesize < 1318912 }
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