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rule win_chthonic_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-12-06" version = "1" description = "Detects win.chthonic." 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.chthonic" 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 = { 7459 4f 8bf0 8bcf d3ee 83e601 } // n = 6, score = 600 // 7459 | je 0x5b // 4f | dec edi // 8bf0 | mov esi, eax // 8bcf | mov ecx, edi // d3ee | shr esi, cl // 83e601 | and esi, 1 $sequence_1 = { 0f845d010000 4f 8bf0 8bcf } // n = 4, score = 600 // 0f845d010000 | je 0x163 // 4f | dec edi // 8bf0 | mov esi, eax // 8bcf | mov ecx, edi $sequence_2 = { 81cf00ffffff 47 8a01 8845ff 8d84bdfcfbffff 8b10 } // n = 6, score = 600 // 81cf00ffffff | or edi, 0xffffff00 // 47 | inc edi // 8a01 | mov al, byte ptr [ecx] // 8845ff | mov byte ptr [ebp - 1], al // 8d84bdfcfbffff | lea eax, [ebp + edi*4 - 0x404] // 8b10 | mov edx, dword ptr [eax] $sequence_3 = { 80e17f 8808 b001 5b c3 55 } // n = 6, score = 600 // 80e17f | and cl, 0x7f // 8808 | mov byte ptr [eax], cl // b001 | mov al, 1 // 5b | pop ebx // c3 | ret // 55 | push ebp $sequence_4 = { 8b75f8 83fe02 0f850d010000 8b4df0 } // n = 4, score = 600 // 8b75f8 | mov esi, dword ptr [ebp - 8] // 83fe02 | cmp esi, 2 // 0f850d010000 | jne 0x113 // 8b4df0 | mov ecx, dword ptr [ebp - 0x10] $sequence_5 = { 016e04 83c703 013e 8b36 83c410 } // n = 5, score = 600 // 016e04 | add dword ptr [esi + 4], ebp // 83c703 | add edi, 3 // 013e | add dword ptr [esi], edi // 8b36 | mov esi, dword ptr [esi] // 83c410 | add esp, 0x10 $sequence_6 = { 5e 0f94c0 5b c9 c3 8b041a } // n = 6, score = 600 // 5e | pop esi // 0f94c0 | sete al // 5b | pop ebx // c9 | leave // c3 | ret // 8b041a | mov eax, dword ptr [edx + ebx] $sequence_7 = { 53 ff7510 ff7508 e8???????? 85c0 } // n = 5, score = 600 // 53 | push ebx // ff7510 | push dword ptr [ebp + 0x10] // ff7508 | push dword ptr [ebp + 8] // e8???????? | // 85c0 | test eax, eax $sequence_8 = { 80e17f 8808 b001 5b c3 55 8bec } // n = 7, score = 600 // 80e17f | and cl, 0x7f // 8808 | mov byte ptr [eax], cl // b001 | mov al, 1 // 5b | pop ebx // c3 | ret // 55 | push ebp // 8bec | mov ebp, esp $sequence_9 = { ff751c ff7518 ff7514 53 ff7510 ff7508 e8???????? } // n = 7, score = 600 // ff751c | push dword ptr [ebp + 0x1c] // ff7518 | push dword ptr [ebp + 0x18] // ff7514 | push dword ptr [ebp + 0x14] // 53 | push ebx // ff7510 | push dword ptr [ebp + 0x10] // ff7508 | push dword ptr [ebp + 8] // e8???????? | condition: 7 of them and filesize < 425984 }
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