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rule win_rapid_ransom_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2022-04-08" version = "1" description = "Detects win.rapid_ransom." 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.rapid_ransom" malpedia_rule_date = "20220405" malpedia_hash = "ecd38294bd47d5589be5cd5490dc8bb4804afc2a" malpedia_version = "20220411" 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 = { 6801000004 6800a40000 ff75f8 ff15???????? } // n = 4, score = 300 // 6801000004 | push 0x4000001 // 6800a40000 | push 0xa400 // ff75f8 | push dword ptr [ebp - 8] // ff15???????? | $sequence_1 = { 8d4001 4e 75f7 ff75fc 51 } // n = 5, score = 200 // 8d4001 | lea eax, dword ptr [eax + 1] // 4e | dec esi // 75f7 | jne 0xfffffff9 // ff75fc | push dword ptr [ebp - 4] // 51 | push ecx $sequence_2 = { c745f0f5000000 c745e86a000000 e8???????? 68f5000000 57 } // n = 5, score = 200 // c745f0f5000000 | mov dword ptr [ebp - 0x10], 0xf5 // c745e86a000000 | mov dword ptr [ebp - 0x18], 0x6a // e8???????? | // 68f5000000 | push 0xf5 // 57 | push edi $sequence_3 = { c644241701 57 6a01 e8???????? 83c410 84c0 0f94c0 } // n = 7, score = 200 // c644241701 | mov byte ptr [esp + 0x17], 1 // 57 | push edi // 6a01 | push 1 // e8???????? | // 83c410 | add esp, 0x10 // 84c0 | test al, al // 0f94c0 | sete al $sequence_4 = { 8bec 51 53 8b5d08 56 8bf2 8975fc } // n = 7, score = 200 // 8bec | mov ebp, esp // 51 | push ecx // 53 | push ebx // 8b5d08 | mov ebx, dword ptr [ebp + 8] // 56 | push esi // 8bf2 | mov esi, edx // 8975fc | mov dword ptr [ebp - 4], esi $sequence_5 = { 8b1d???????? 56 57 33ff be???????? ffd3 } // n = 6, score = 200 // 8b1d???????? | // 56 | push esi // 57 | push edi // 33ff | xor edi, edi // be???????? | // ffd3 | call ebx $sequence_6 = { 8b75fc 5b 56 ff15???????? 50 56 ff15???????? } // n = 7, score = 200 // 8b75fc | mov esi, dword ptr [ebp - 4] // 5b | pop ebx // 56 | push esi // ff15???????? | // 50 | push eax // 56 | push esi // ff15???????? | $sequence_7 = { e8???????? 68f5000000 8d87f5000000 8d8e00010000 50 51 894dec } // n = 7, score = 200 // e8???????? | // 68f5000000 | push 0xf5 // 8d87f5000000 | lea eax, dword ptr [edi + 0xf5] // 8d8e00010000 | lea ecx, dword ptr [esi + 0x100] // 50 | push eax // 51 | push ecx // 894dec | mov dword ptr [ebp - 0x14], ecx $sequence_8 = { 8b4df0 0f1f4000 660f1f840000000000 8bb31c010000 83be7004000000 7412 } // n = 6, score = 100 // 8b4df0 | mov ecx, dword ptr [ebp - 0x10] // 0f1f4000 | nop dword ptr [eax] // 660f1f840000000000 | nop word ptr [eax + eax] // 8bb31c010000 | mov esi, dword ptr [ebx + 0x11c] // 83be7004000000 | cmp dword ptr [esi + 0x470], 0 // 7412 | je 0x14 $sequence_9 = { 0f8497000000 6a00 50 ff75fc } // n = 4, score = 100 // 0f8497000000 | je 0x9d // 6a00 | push 0 // 50 | push eax // ff75fc | push dword ptr [ebp - 4] $sequence_10 = { 83e801 79f4 2bf1 46 8d4601 50 e8???????? } // n = 7, score = 100 // 83e801 | sub eax, 1 // 79f4 | jns 0xfffffff6 // 2bf1 | sub esi, ecx // 46 | inc esi // 8d4601 | lea eax, dword ptr [esi + 1] // 50 | push eax // e8???????? | $sequence_11 = { 7408 c644240f01 884814 8b780c 85ff } // n = 5, score = 100 // 7408 | je 0xa // c644240f01 | mov byte ptr [esp + 0xf], 1 // 884814 | mov byte ptr [eax + 0x14], cl // 8b780c | mov edi, dword ptr [eax + 0xc] // 85ff | test edi, edi $sequence_12 = { eb02 33c0 8b3d???????? 6a00 8945b8 } // n = 5, score = 100 // eb02 | jmp 4 // 33c0 | xor eax, eax // 8b3d???????? | // 6a00 | push 0 // 8945b8 | mov dword ptr [ebp - 0x48], eax $sequence_13 = { 6a02 e8???????? 83c404 8b8674040000 83f8ff 7411 50 } // n = 7, score = 100 // 6a02 | push 2 // e8???????? | // 83c404 | add esp, 4 // 8b8674040000 | mov eax, dword ptr [esi + 0x474] // 83f8ff | cmp eax, -1 // 7411 | je 0x13 // 50 | push eax $sequence_14 = { 33c0 8945e8 57 33ff } // n = 4, score = 100 // 33c0 | xor eax, eax // 8945e8 | mov dword ptr [ebp - 0x18], eax // 57 | push edi // 33ff | xor edi, edi condition: 7 of them and filesize < 286720 }
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