Actor(s): FIN7
A Trojan for Winows with the same code structure and functionalities of elf.rekoobe, for Linux environment instead.
rule win_rekoobew_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2022-04-08" version = "1" description = "Detects win.rekoobew." 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.rekoobew" 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 = { 89c2 83ec04 85d2 b800000000 7413 } // n = 5, score = 100 // 89c2 | mov edx, eax // 83ec04 | sub esp, 4 // 85d2 | test edx, edx // b800000000 | mov eax, 0 // 7413 | je 0x15 $sequence_1 = { 8b35???????? f3a6 0f97c2 0f92c0 38c2 7415 c7442404???????? } // n = 7, score = 100 // 8b35???????? | // f3a6 | repe cmpsb byte ptr [esi], byte ptr es:[edi] // 0f97c2 | seta dl // 0f92c0 | setb al // 38c2 | cmp dl, al // 7415 | je 0x17 // c7442404???????? | $sequence_2 = { 837df00c 0f8ee4010000 8d7710 8975e0 0fb6da 8b349de0904000 337710 } // n = 7, score = 100 // 837df00c | cmp dword ptr [ebp - 0x10], 0xc // 0f8ee4010000 | jle 0x1ea // 8d7710 | lea esi, dword ptr [edi + 0x10] // 8975e0 | mov dword ptr [ebp - 0x20], esi // 0fb6da | movzx ebx, dl // 8b349de0904000 | mov esi, dword ptr [ebx*4 + 0x4090e0] // 337710 | xor esi, dword ptr [edi + 0x10] $sequence_3 = { 53 83ec20 c645f700 bb00000000 8d75f7 c744240c00000000 c744240801000000 } // n = 7, score = 100 // 53 | push ebx // 83ec20 | sub esp, 0x20 // c645f700 | mov byte ptr [ebp - 9], 0 // bb00000000 | mov ebx, 0 // 8d75f7 | lea esi, dword ptr [ebp - 9] // c744240c00000000 | mov dword ptr [esp + 0xc], 0 // c744240801000000 | mov dword ptr [esp + 8], 1 $sequence_4 = { 891c24 e8???????? 3b45d4 7568 8b55bc 8b45c4 855485e0 } // n = 7, score = 100 // 891c24 | mov dword ptr [esp], ebx // e8???????? | // 3b45d4 | cmp eax, dword ptr [ebp - 0x2c] // 7568 | jne 0x6a // 8b55bc | mov edx, dword ptr [ebp - 0x44] // 8b45c4 | mov eax, dword ptr [ebp - 0x3c] // 855485e0 | test dword ptr [ebp + eax*4 - 0x20], edx $sequence_5 = { b8ffffffff eb45 b8ffffffff eb3e b8ffffffff eb37 b8ffffffff } // n = 7, score = 100 // b8ffffffff | mov eax, 0xffffffff // eb45 | jmp 0x47 // b8ffffffff | mov eax, 0xffffffff // eb3e | jmp 0x40 // b8ffffffff | mov eax, 0xffffffff // eb37 | jmp 0x39 // b8ffffffff | mov eax, 0xffffffff $sequence_6 = { 335ddc 335dd4 d1c3 895dc8 8d8c19d6c162ca 894df0 89d1 } // n = 7, score = 100 // 335ddc | xor ebx, dword ptr [ebp - 0x24] // 335dd4 | xor ebx, dword ptr [ebp - 0x2c] // d1c3 | rol ebx, 1 // 895dc8 | mov dword ptr [ebp - 0x38], ebx // 8d8c19d6c162ca | lea ecx, dword ptr [ecx + ebx - 0x359d3e2a] // 894df0 | mov dword ptr [ebp - 0x10], ecx // 89d1 | mov ecx, edx $sequence_7 = { 83ec1c a1???????? 890424 e8???????? 8b1d???????? 890424 e8???????? } // n = 7, score = 100 // 83ec1c | sub esp, 0x1c // a1???????? | // 890424 | mov dword ptr [esp], eax // e8???????? | // 8b1d???????? | // 890424 | mov dword ptr [esp], eax // e8???????? | $sequence_8 = { 33348de0844000 8b4ddc c1e910 0fb6c9 } // n = 4, score = 100 // 33348de0844000 | xor esi, dword ptr [ecx*4 + 0x4084e0] // 8b4ddc | mov ecx, dword ptr [ebp - 0x24] // c1e910 | shr ecx, 0x10 // 0fb6c9 | movzx ecx, cl $sequence_9 = { 89c7 09df 21f7 89c2 21da 09fa 0355f0 } // n = 7, score = 100 // 89c7 | mov edi, eax // 09df | or edi, ebx // 21f7 | and edi, esi // 89c2 | mov edx, eax // 21da | and edx, ebx // 09fa | or edx, edi // 0355f0 | add edx, dword ptr [ebp - 0x10] condition: 7 of them and filesize < 248832 }
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