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rule win_downeks_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-01-25" 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 = "20230124" malpedia_hash = "2ee0eebba83dce3d019a90519f2f972c0fcf9686" malpedia_version = "20230125" 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 = { c1cf07 33cf 8bbd38ffffff c1ef03 33cf 03cb 038d34ffffff } // n = 7, score = 200 // c1cf07 | ror edi, 7 // 33cf | xor ecx, edi // 8bbd38ffffff | mov edi, dword ptr [ebp - 0xc8] // c1ef03 | shr edi, 3 // 33cf | xor ecx, edi // 03cb | add ecx, ebx // 038d34ffffff | add ecx, dword ptr [ebp - 0xcc] $sequence_1 = { e8???????? 6aff 6a00 8d8db0fdffff 51 e8???????? 6a04 } // n = 7, score = 200 // e8???????? | // 6aff | push -1 // 6a00 | push 0 // 8d8db0fdffff | lea ecx, [ebp - 0x250] // 51 | push ecx // e8???????? | // 6a04 | push 4 $sequence_2 = { 0bd7 0fb67804 89548dbc 0fb65005 c1e208 0bd7 0fb67803 } // n = 7, score = 200 // 0bd7 | or edx, edi // 0fb67804 | movzx edi, byte ptr [eax + 4] // 89548dbc | mov dword ptr [ebp + ecx*4 - 0x44], edx // 0fb65005 | movzx edx, byte ptr [eax + 5] // c1e208 | shl edx, 8 // 0bd7 | or edx, edi // 0fb67803 | movzx edi, byte ptr [eax + 3] $sequence_3 = { e8???????? 83c418 eb1c 8b96f4860000 8b8ed0860000 52 50 } // n = 7, score = 200 // e8???????? | // 83c418 | add esp, 0x18 // eb1c | jmp 0x1e // 8b96f4860000 | mov edx, dword ptr [esi + 0x86f4] // 8b8ed0860000 | mov ecx, dword ptr [esi + 0x86d0] // 52 | push edx // 50 | push eax $sequence_4 = { 8d5801 8a08 40 84c9 75f9 2bc3 2bc2 } // n = 7, score = 200 // 8d5801 | lea ebx, [eax + 1] // 8a08 | mov cl, byte ptr [eax] // 40 | inc eax // 84c9 | test cl, cl // 75f9 | jne 0xfffffffb // 2bc3 | sub eax, ebx // 2bc2 | sub eax, edx $sequence_5 = { c745fc01000000 84c9 7507 ba04000000 eb66 8b5d14 8b7d10 } // n = 7, score = 200 // c745fc01000000 | mov dword ptr [ebp - 4], 1 // 84c9 | test cl, cl // 7507 | jne 9 // ba04000000 | mov edx, 4 // eb66 | jmp 0x68 // 8b5d14 | mov ebx, dword ptr [ebp + 0x14] // 8b7d10 | mov edi, dword ptr [ebp + 0x10] $sequence_6 = { 8d9b00000000 40 803800 75fa b9dc2b0904 2bc1 50 } // n = 7, score = 200 // 8d9b00000000 | lea ebx, [ebx] // 40 | inc eax // 803800 | cmp byte ptr [eax], 0 // 75fa | jne 0xfffffffc // b9dc2b0904 | mov ecx, 0x4092bdc // 2bc1 | sub eax, ecx // 50 | push eax $sequence_7 = { 85f6 74a8 8bc3 56 50 e8???????? 56 } // n = 7, score = 200 // 85f6 | test esi, esi // 74a8 | je 0xffffffaa // 8bc3 | mov eax, ebx // 56 | push esi // 50 | push eax // e8???????? | // 56 | push esi $sequence_8 = { 8bcf e8???????? 8b0f 8d04b6 8b7704 8d1cc1 8975f0 } // n = 7, score = 200 // 8bcf | mov ecx, edi // e8???????? | // 8b0f | mov ecx, dword ptr [edi] // 8d04b6 | lea eax, [esi + esi*4] // 8b7704 | mov esi, dword ptr [edi + 4] // 8d1cc1 | lea ebx, [ecx + eax*8] // 8975f0 | mov dword ptr [ebp - 0x10], esi $sequence_9 = { 03c9 03c0 03c9 52 e8???????? 8906 897e08 } // n = 7, score = 200 // 03c9 | add ecx, ecx // 03c0 | add eax, eax // 03c9 | add ecx, ecx // 52 | push edx // e8???????? | // 8906 | mov dword ptr [esi], eax // 897e08 | mov dword ptr [esi + 8], edi condition: 7 of them and filesize < 1318912 }
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