Backdoor written in Nim.
rule win_nimrev_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2022-05-16" version = "1" description = "Detects win.nimrev." 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.nimrev" malpedia_rule_date = "20220513" malpedia_hash = "7f4b2229e6ae614d86d74917f6d5b41890e62a26" malpedia_version = "20220516" 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 = { 66c700fdff 90 e9???????? 90 } // n = 4, score = 200 // 66c700fdff | lea eax, [0x268ec] // 90 | dec eax // e9???????? | // 90 | mov dword ptr [ebp - 0x28], eax $sequence_1 = { 89c1 e8???????? eb04 90 eb01 90 } // n = 6, score = 200 // 89c1 | dec eax // e8???????? | // eb04 | mov ecx, eax // 90 | dec eax // eb01 | lea eax, [0x25ee0] // 90 | dec eax $sequence_2 = { 0fb600 3c5f 7507 b801000000 eb05 } // n = 5, score = 200 // 0fb600 | mov dword ptr [esp], eax // 3c5f | mov dword ptr [ebp - 0x14], 0 // 7507 | mov eax, dword ptr [ebp - 0x3c] // b801000000 | mov eax, dword ptr [eax + 4] // eb05 | add eax, 1 $sequence_3 = { 0fb600 3c39 7707 b801000000 eb05 } // n = 5, score = 200 // 0fb600 | mov dword ptr [ebp - 0xc], 0 // 3c39 | nop // 7707 | mov dword ptr [ebp - 0x18], 0xfa // b801000000 | mov dword ptr [ebp - 0x14], 0x422a78 // eb05 | mov eax, dword ptr [ebp - 0x2c] $sequence_4 = { 90 e9???????? 90 b9d0070000 } // n = 4, score = 200 // 90 | mov dword ptr [ebp - 0x70], 0xb8 // e9???????? | // 90 | mov ecx, eax // b9d0070000 | dec eax $sequence_5 = { 90 e9???????? 90 eb01 } // n = 4, score = 200 // 90 | mov dword ptr [ebp - 0x28], eax // e9???????? | // 90 | mov dword ptr [esp + 4], 2 // eb01 | mov ecx, eax $sequence_6 = { 90 eb01 90 e8???????? 90 } // n = 5, score = 200 // 90 | mov dword ptr [esp], eax // eb01 | mov dword ptr [ebp - 0x14], 0x6a1 // 90 | mov dword ptr [ebp - 0x10], 0x423a08 // e8???????? | // 90 | mov ebx, dword ptr [ebp - 0x2c] $sequence_7 = { 0f97c0 8845ef eb01 90 807def00 } // n = 5, score = 200 // 0f97c0 | mov eax, dword ptr [eax] // 8845ef | mov dword ptr [ebp - 0x18], 0x379 // eb01 | mov dword ptr [ebp - 0x14], 0x4244a9 // 90 | mov eax, dword ptr [ebp - 0x2c] // 807def00 | mov ecx, eax $sequence_8 = { e8???????? e8???????? eb04 90 } // n = 4, score = 200 // e8???????? | // e8???????? | // eb04 | mov dword ptr [esp + 0xc], 0 // 90 | mov eax, dword ptr [ebp - 0x10] $sequence_9 = { d3ea 89d0 83e001 85c0 } // n = 4, score = 200 // d3ea | add eax, edx // 89d0 | mov ecx, eax // 83e001 | mov eax, 0 // 85c0 | sub eax, dword ptr [ebp - 0x44] condition: 7 of them and filesize < 1141760 }
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