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rule win_vhd_ransomware_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-12-06" version = "1" description = "Detects win.vhd_ransomware." 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.vhd_ransomware" 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 = { 8b450c 4a 3bd0 7d10 8bc8 } // n = 5, score = 100 // 8b450c | mov eax, dword ptr [ebp + 0xc] // 4a | dec edx // 3bd0 | cmp edx, eax // 7d10 | jge 0x12 // 8bc8 | mov ecx, eax $sequence_1 = { 68???????? 8d45f4 50 c745f4d8514100 e8???????? cc 8bff } // n = 7, score = 100 // 68???????? | // 8d45f4 | lea eax, [ebp - 0xc] // 50 | push eax // c745f4d8514100 | mov dword ptr [ebp - 0xc], 0x4151d8 // e8???????? | // cc | int3 // 8bff | mov edi, edi $sequence_2 = { e8???????? 8b8514e6ffff 48 83c404 4b 898514e6ffff 85c0 } // n = 7, score = 100 // e8???????? | // 8b8514e6ffff | mov eax, dword ptr [ebp - 0x19ec] // 48 | dec eax // 83c404 | add esp, 4 // 4b | dec ebx // 898514e6ffff | mov dword ptr [ebp - 0x19ec], eax // 85c0 | test eax, eax $sequence_3 = { f3ab 8b8dccfcffff 890a 85c9 7e98 8d4a04 } // n = 6, score = 100 // f3ab | rep stosd dword ptr es:[edi], eax // 8b8dccfcffff | mov ecx, dword ptr [ebp - 0x334] // 890a | mov dword ptr [edx], ecx // 85c9 | test ecx, ecx // 7e98 | jle 0xffffff9a // 8d4a04 | lea ecx, [edx + 4] $sequence_4 = { c1eb18 0fb69b98744100 c1e308 0bda 8b55cc c1ea08 0fb6d2 } // n = 7, score = 100 // c1eb18 | shr ebx, 0x18 // 0fb69b98744100 | movzx ebx, byte ptr [ebx + 0x417498] // c1e308 | shl ebx, 8 // 0bda | or ebx, edx // 8b55cc | mov edx, dword ptr [ebp - 0x34] // c1ea08 | shr edx, 8 // 0fb6d2 | movzx edx, dl $sequence_5 = { 66895c2460 897c241c c7442420c05d4000 897c2424 897c2428 } // n = 5, score = 100 // 66895c2460 | mov word ptr [esp + 0x60], bx // 897c241c | mov dword ptr [esp + 0x1c], edi // c7442420c05d4000 | mov dword ptr [esp + 0x20], 0x405dc0 // 897c2424 | mov dword ptr [esp + 0x24], edi // 897c2428 | mov dword ptr [esp + 0x28], edi $sequence_6 = { 7d10 895c8204 ff02 8bde 33f6 8bcb 0bce } // n = 7, score = 100 // 7d10 | jge 0x12 // 895c8204 | mov dword ptr [edx + eax*4 + 4], ebx // ff02 | inc dword ptr [edx] // 8bde | mov ebx, esi // 33f6 | xor esi, esi // 8bcb | mov ecx, ebx // 0bce | or ecx, esi $sequence_7 = { e8???????? b9c9000000 8bf0 8dbd7cf6ffff } // n = 4, score = 100 // e8???????? | // b9c9000000 | mov ecx, 0xc9 // 8bf0 | mov esi, eax // 8dbd7cf6ffff | lea edi, [ebp - 0x984] $sequence_8 = { 46 83fe40 7cee 8d4d9c 51 8d8d84baffff e8???????? } // n = 7, score = 100 // 46 | inc esi // 83fe40 | cmp esi, 0x40 // 7cee | jl 0xfffffff0 // 8d4d9c | lea ecx, [ebp - 0x64] // 51 | push ecx // 8d8d84baffff | lea ecx, [ebp - 0x457c] // e8???????? | $sequence_9 = { ff15???????? 32c0 e9???????? 6a00 8d8588b4ffff 50 6800200000 } // n = 7, score = 100 // ff15???????? | // 32c0 | xor al, al // e9???????? | // 6a00 | push 0 // 8d8588b4ffff | lea eax, [ebp - 0x4b78] // 50 | push eax // 6800200000 | push 0x2000 condition: 7 of them and filesize < 275456 }
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