Ransomware.
rule win_fct_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-12-06" version = "1" description = "Detects win.fct." 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.fct" malpedia_rule_date = "20231130" malpedia_hash = "fc8a0e9f343f6d6ded9e7df1a64dac0cc68d7351" malpedia_version = "20230808" 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 = { 83e801 0f8595010000 c745e438324100 e9???????? 894de0 c745e438324100 e9???????? } // n = 7, score = 100 // 83e801 | sub eax, 1 // 0f8595010000 | jne 0x19b // c745e438324100 | mov dword ptr [ebp - 0x1c], 0x413238 // e9???????? | // 894de0 | mov dword ptr [ebp - 0x20], ecx // c745e438324100 | mov dword ptr [ebp - 0x1c], 0x413238 // e9???????? | $sequence_1 = { c3 c705????????80554100 b001 c3 68???????? e8???????? c70424???????? } // n = 7, score = 100 // c3 | ret // c705????????80554100 | // b001 | mov al, 1 // c3 | ret // 68???????? | // e8???????? | // c70424???????? | $sequence_2 = { e9???????? 8b1f 8d049d58634100 8b30 } // n = 4, score = 100 // e9???????? | // 8b1f | mov ebx, dword ptr [edi] // 8d049d58634100 | lea eax, [ebx*4 + 0x416358] // 8b30 | mov esi, dword ptr [eax] $sequence_3 = { 8bc6 83e03f 6bc838 894de0 8b049d50614100 f644082801 7469 } // n = 7, score = 100 // 8bc6 | mov eax, esi // 83e03f | and eax, 0x3f // 6bc838 | imul ecx, eax, 0x38 // 894de0 | mov dword ptr [ebp - 0x20], ecx // 8b049d50614100 | mov eax, dword ptr [ebx*4 + 0x416150] // f644082801 | test byte ptr [eax + ecx + 0x28], 1 // 7469 | je 0x6b $sequence_4 = { 6a04 e8???????? 83bd48fdffff08 8d8d34fdffff 8d45d8 } // n = 5, score = 100 // 6a04 | push 4 // e8???????? | // 83bd48fdffff08 | cmp dword ptr [ebp - 0x2b8], 8 // 8d8d34fdffff | lea ecx, [ebp - 0x2cc] // 8d45d8 | lea eax, [ebp - 0x28] $sequence_5 = { c70021000000 eb44 c745e002000000 c745e444324100 8b4508 8bcf 8b7510 } // n = 7, score = 100 // c70021000000 | mov dword ptr [eax], 0x21 // eb44 | jmp 0x46 // c745e002000000 | mov dword ptr [ebp - 0x20], 2 // c745e444324100 | mov dword ptr [ebp - 0x1c], 0x413244 // 8b4508 | mov eax, dword ptr [ebp + 8] // 8bcf | mov ecx, edi // 8b7510 | mov esi, dword ptr [ebp + 0x10] $sequence_6 = { 50 8b04bd50614100 ff743018 ff15???????? 85c0 7404 b001 } // n = 7, score = 100 // 50 | push eax // 8b04bd50614100 | mov eax, dword ptr [edi*4 + 0x416150] // ff743018 | push dword ptr [eax + esi + 0x18] // ff15???????? | // 85c0 | test eax, eax // 7404 | je 6 // b001 | mov al, 1 $sequence_7 = { 56 33f6 8b8650614100 85c0 740e 50 e8???????? } // n = 7, score = 100 // 56 | push esi // 33f6 | xor esi, esi // 8b8650614100 | mov eax, dword ptr [esi + 0x416150] // 85c0 | test eax, eax // 740e | je 0x10 // 50 | push eax // e8???????? | $sequence_8 = { 660fd60f 8d7f08 8b048d84514000 ffe0 f7c703000000 7413 } // n = 6, score = 100 // 660fd60f | movq qword ptr [edi], xmm1 // 8d7f08 | lea edi, [edi + 8] // 8b048d84514000 | mov eax, dword ptr [ecx*4 + 0x405184] // ffe0 | jmp eax // f7c703000000 | test edi, 3 // 7413 | je 0x15 $sequence_9 = { 68???????? c68524fdffff00 8d4dd8 ffb524fdffff 6a01 e8???????? } // n = 6, score = 100 // 68???????? | // c68524fdffff00 | mov byte ptr [ebp - 0x2dc], 0 // 8d4dd8 | lea ecx, [ebp - 0x28] // ffb524fdffff | push dword ptr [ebp - 0x2dc] // 6a01 | push 1 // e8???????? | condition: 7 of them and filesize < 204800 }
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