Ransomware.
rule win_fct_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-07-11" 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 = "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 = { 83cfff 897de4 8365fc00 8b049d50614100 8b4de0 } // n = 5, score = 100 // 83cfff | or edi, 0xffffffff // 897de4 | mov dword ptr [ebp - 0x1c], edi // 8365fc00 | and dword ptr [ebp - 4], 0 // 8b049d50614100 | mov eax, dword ptr [ebx*4 + 0x416150] // 8b4de0 | mov ecx, dword ptr [ebp - 0x20] $sequence_1 = { c1fa06 6bc838 8b049550614100 f644082801 } // n = 4, score = 100 // c1fa06 | sar edx, 6 // 6bc838 | imul ecx, eax, 0x38 // 8b049550614100 | mov eax, dword ptr [edx*4 + 0x416150] // f644082801 | test byte ptr [eax + ecx + 0x28], 1 $sequence_2 = { 58 6bc000 c7806c59410002000000 6a04 58 6bc000 } // n = 6, score = 100 // 58 | pop eax // 6bc000 | imul eax, eax, 0 // c7806c59410002000000 | mov dword ptr [eax + 0x41596c], 2 // 6a04 | push 4 // 58 | pop eax // 6bc000 | imul eax, eax, 0 $sequence_3 = { 8bf0 d1fe 6a55 ff34f570204100 ff7508 } // n = 5, score = 100 // 8bf0 | mov esi, eax // d1fe | sar esi, 1 // 6a55 | push 0x55 // ff34f570204100 | push dword ptr [esi*8 + 0x412070] // ff7508 | push dword ptr [ebp + 8] $sequence_4 = { c745e003000000 e9???????? c745e440324100 ebb8 } // n = 4, score = 100 // c745e003000000 | mov dword ptr [ebp - 0x20], 3 // e9???????? | // c745e440324100 | mov dword ptr [ebp - 0x1c], 0x413240 // ebb8 | jmp 0xffffffba $sequence_5 = { 53 ff15???????? 85c0 740b 8bbd0cfdffff e9???????? } // n = 6, score = 100 // 53 | push ebx // ff15???????? | // 85c0 | test eax, eax // 740b | je 0xd // 8bbd0cfdffff | mov edi, dword ptr [ebp - 0x2f4] // e9???????? | $sequence_6 = { 8b55e8 2bc2 83f801 7221 } // n = 4, score = 100 // 8b55e8 | mov edx, dword ptr [ebp - 0x18] // 2bc2 | sub eax, edx // 83f801 | cmp eax, 1 // 7221 | jb 0x23 $sequence_7 = { 6bf838 8955f8 8b149550614100 897df4 8a5c3a29 80fb02 7405 } // n = 7, score = 100 // 6bf838 | imul edi, eax, 0x38 // 8955f8 | mov dword ptr [ebp - 8], edx // 8b149550614100 | mov edx, dword ptr [edx*4 + 0x416150] // 897df4 | mov dword ptr [ebp - 0xc], edi // 8a5c3a29 | mov bl, byte ptr [edx + edi + 0x29] // 80fb02 | cmp bl, 2 // 7405 | je 7 $sequence_8 = { 8b1f 8d049d58634100 8b30 8945fc 90 85f6 } // n = 6, score = 100 // 8b1f | mov ebx, dword ptr [edi] // 8d049d58634100 | lea eax, [ebx*4 + 0x416358] // 8b30 | mov esi, dword ptr [eax] // 8945fc | mov dword ptr [ebp - 4], eax // 90 | nop // 85f6 | test esi, esi $sequence_9 = { eb07 c745e444324100 8b4508 8bcf 8b7510 c745e001000000 dd00 } // n = 7, score = 100 // eb07 | jmp 9 // 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] // c745e001000000 | mov dword ptr [ebp - 0x20], 1 // dd00 | fld qword ptr [eax] condition: 7 of them and filesize < 204800 }
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