Backdoor written in Nim.
rule win_nimrev_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-01-25" 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 = "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 = { 0f95c0 8845f6 eb01 90 0fb645f6 8845f7 } // n = 6, score = 200 // 0f95c0 | mov dword ptr [ebp - 0x1c], 0x422df8 // 8845f6 | mov edx, dword ptr [ebp - 0x30] // eb01 | mov eax, dword ptr [ebp - 0x2c] // 90 | mov ecx, eax // 0fb645f6 | mov dword ptr [ebp - 0x1c], 0x422df8 // 8845f7 | mov byte ptr [ebp - 9], 0 $sequence_1 = { 3c39 7707 b801000000 eb05 } // n = 4, score = 200 // 3c39 | mov eax, dword ptr [ebp + 8] // 7707 | sub eax, 1 // b801000000 | cmp edx, eax // eb05 | jb 0x60a $sequence_2 = { 0fb600 0fb6c0 83f85c 7432 83f85c } // n = 5, score = 200 // 0fb600 | jmp 0x3f // 0fb6c0 | nop // 83f85c | dec eax // 7432 | mov dword ptr [ebp], 0x267 // 83f85c | dec eax $sequence_3 = { e8???????? eb04 90 eb01 90 90 } // n = 6, score = 200 // e8???????? | // eb04 | mov eax, dword ptr [ebp - 0xc] // 90 | movzx ecx, ax // eb01 | mov dword ptr [esp], ecx // 90 | mov ecx, eax // 90 | cmp dword ptr [ebp + 8], eax $sequence_4 = { e8???????? e8???????? eb04 90 } // n = 4, score = 200 // e8???????? | // e8???????? | // eb04 | mov dword ptr [ebp - 0x40], eax // 90 | dec eax $sequence_5 = { 8845e7 eb01 90 807de700 } // n = 4, score = 200 // 8845e7 | push ebx // eb01 | dec eax // 90 | sub esp, 0x28 // 807de700 | dec eax $sequence_6 = { 90 eb01 90 e8???????? 90 } // n = 5, score = 200 // 90 | nop // eb01 | jmp 0x151 // 90 | nop // e8???????? | // 90 | mov dword ptr [ebp - 0xc], eax $sequence_7 = { 0fb600 3c39 7707 b801000000 } // n = 4, score = 200 // 0fb600 | je 0x264 // 3c39 | imul eax, dword ptr [ebp - 0x18] // 7707 | mov edx, dword ptr [ebp - 0x3c] // b801000000 | add edx, 8 $sequence_8 = { 0f93c0 83f001 84c0 7408 } // n = 4, score = 200 // 0f93c0 | lea eax, [0x100d9] // 83f001 | dec eax // 84c0 | mov dword ptr [ebp - 0x48], eax // 7408 | jle 0x73e $sequence_9 = { eb05 b800000000 8845f7 eb01 90 } // n = 5, score = 200 // eb05 | cmp dword ptr [ebp - 0x18], 0 // b800000000 | jg 0x12b8 // 8845f7 | mov dword ptr [ebp - 0x44], 0x40f // eb01 | mov dword ptr [ebp - 0x44], 0x40e // 90 | mov dword ptr [ebp - 0x40], 0x42431a condition: 7 of them and filesize < 1141760 }
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