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rule win_chthonic_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-01-25" 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 = "20230124" malpedia_hash = "2ee0eebba83dce3d019a90519f2f972c0fcf9686" malpedia_version = "20230125" 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 = { 81cf00ffffff 47 8a01 8845ff 8d84bdfcfbffff } // n = 5, 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] $sequence_1 = { 81e1ff00ff00 0bc1 89470c 5f } // n = 4, score = 600 // 81e1ff00ff00 | and ecx, 0xff00ff // 0bc1 | or eax, ecx // 89470c | mov dword ptr [edi + 0xc], eax // 5f | pop edi $sequence_2 = { 83c410 f60680 7408 8a06 32c3 247f } // n = 6, score = 600 // 83c410 | add esp, 0x10 // f60680 | test byte ptr [esi], 0x80 // 7408 | je 0xa // 8a06 | mov al, byte ptr [esi] // 32c3 | xor al, bl // 247f | and al, 0x7f $sequence_3 = { 5f c1ee1f eba3 8b041a 6a1f } // n = 5, score = 600 // 5f | pop edi // c1ee1f | shr esi, 0x1f // eba3 | jmp 0xffffffa5 // 8b041a | mov eax, dword ptr [edx + ebx] // 6a1f | push 0x1f $sequence_4 = { 81ce00ffffff 46 8d84b5fcfbffff 8b08 } // n = 4, score = 600 // 81ce00ffffff | or esi, 0xffffff00 // 46 | inc esi // 8d84b5fcfbffff | lea eax, [ebp + esi*4 - 0x404] // 8b08 | mov ecx, dword ptr [eax] $sequence_5 = { 016e04 83c703 013e 8b36 83c410 f60680 7408 } // n = 7, 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 // f60680 | test byte ptr [esi], 0x80 // 7408 | je 0xa $sequence_6 = { 8bc1 c1c808 2500ff00ff c1c108 81e1ff00ff00 0bc1 89470c } // n = 7, score = 600 // 8bc1 | mov eax, ecx // c1c808 | ror eax, 8 // 2500ff00ff | and eax, 0xff00ff00 // c1c108 | rol ecx, 8 // 81e1ff00ff00 | and ecx, 0xff00ff // 0bc1 | or eax, ecx // 89470c | mov dword ptr [edi + 0xc], eax $sequence_7 = { c1ee1f eba3 8b041a 6a1f 8bf0 } // n = 5, score = 600 // c1ee1f | shr esi, 0x1f // eba3 | jmp 0xffffffa5 // 8b041a | mov eax, dword ptr [edx + ebx] // 6a1f | push 0x1f // 8bf0 | mov esi, eax $sequence_8 = { 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_9 = { 7908 4f 81cf00ffffff 47 8a01 8845ff 8d84bdfcfbffff } // n = 7, score = 600 // 7908 | jns 0xa // 4f | dec edi // 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] condition: 7 of them and filesize < 425984 }
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