Actor(s): Lazarus Group
A downloader that uses Windows messages to control its execution flow.
rule win_scout_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2026-01-05" version = "1" description = "Detects win.scout." 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.scout" malpedia_rule_date = "20260105" malpedia_hash = "19b79e7cab4eaf532122e5b45a77dd8f6bb5cc79" malpedia_version = "20251219" 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 = { 817c243031313131 7445 690d????????60ea0000 ff15???????? 8b0d???????? b867666666 ffc1 } // n = 7, score = 100 // 817c243031313131 | test eax, eax // 7445 | je 0x17c // 690d????????60ea0000 | // ff15???????? | // 8b0d???????? | // b867666666 | dec eax // ffc1 | sub esp, 0x28 $sequence_1 = { 8d58b0 498bce 448bc3 488d154cac0000 e8???????? 85c0 } // n = 6, score = 100 // 8d58b0 | and ecx, 0x3f // 498bce | dec eax // 448bc3 | sar eax, 6 // 488d154cac0000 | inc ebp // e8???????? | // 85c0 | xor edi, edi $sequence_2 = { 7706 ff15???????? 488364243000 488d0d849f0000 8364242800 41b803000000 4533c9 } // n = 7, score = 100 // 7706 | mov ebx, ecx // ff15???????? | // 488364243000 | dec eax // 488d0d849f0000 | cmp ecx, eax // 8364242800 | je 0x12e4 // 41b803000000 | mov eax, dword ptr [ecx + 0x15c] // 4533c9 | test eax, eax $sequence_3 = { 83c8ff eb0b 4803f6 418b84f728950100 } // n = 4, score = 100 // 83c8ff | lea edi, [0x15fcd] // eb0b | dec eax // 4803f6 | mov ecx, dword ptr [ebx + edi] // 418b84f728950100 | dec eax $sequence_4 = { 0f84aa000000 83f81a 0f85eb020000 33ff 488d4c2430 48897c2430 } // n = 6, score = 100 // 0f84aa000000 | lea edx, [0xc025] // 83f81a | dec eax // 0f85eb020000 | test eax, eax // 33ff | je 0x1563 // 488d4c2430 | dec eax // 48897c2430 | mov edx, ebx $sequence_5 = { 488b8d80140000 ff15???????? 488d537c 41b888140000 } // n = 4, score = 100 // 488b8d80140000 | add edi, ecx // ff15???????? | // 488d537c | dec eax // 41b888140000 | sub eax, 1 $sequence_6 = { 4885c9 750b 488d0d29f10000 48894b48 4963d0 e8???????? } // n = 6, score = 100 // 4885c9 | cmp ecx, dword ptr [edx] // 750b | je 0x979 // 488d0d29f10000 | dec esp // 48894b48 | lea ecx, [0xffff04ea] // 4963d0 | dec esp // e8???????? | $sequence_7 = { 488d0d36fbfeff 83e03f 458be9 4d03e8 4c8945df 4c8be6 } // n = 6, score = 100 // 488d0d36fbfeff | mov ecx, dword ptr [eax + 0x205b0] // 83e03f | mov ecx, dword ptr [esp + 0x48] // 458be9 | dec eax // 4d03e8 | lea edx, [0xffff14d2] // 4c8945df | sub ecx, dword ptr [esp + 0x4c] // 4c8be6 | inc ecx $sequence_8 = { 488d0dd4f90000 4183e23f 4d03f0 4d8bf8 } // n = 4, score = 100 // 488d0dd4f90000 | mov dword ptr [esp + 0x20], eax // 4183e23f | dec eax // 4d03f0 | mov edi, eax // 4d8bf8 | dec eax $sequence_9 = { 0f84aa000000 83f81a 0f85eb020000 33ff 488d4c2430 48897c2430 e8???????? } // n = 7, score = 100 // 0f84aa000000 | lea edi, [0x135e0] // 83f81a | dec eax // 0f85eb020000 | sub edi, esi // 33ff | mov al, byte ptr [edi + ebx] // 488d4c2430 | mov byte ptr [ebx], al // 48897c2430 | dec eax // e8???????? | condition: 7 of them and filesize < 315392 }
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