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rule win_absentloader_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-01-25" version = "1" description = "Detects win.absentloader." 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.absentloader" 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 = { c645fc05 8d8da8fcffff 50 51 8d8dc8faffff e8???????? 68048701fd } // n = 7, score = 200 // c645fc05 | mov byte ptr [ebp - 4], 5 // 8d8da8fcffff | lea ecx, [ebp - 0x358] // 50 | push eax // 51 | push ecx // 8d8dc8faffff | lea ecx, [ebp - 0x538] // e8???????? | // 68048701fd | push 0xfd018704 $sequence_1 = { 68a81606fd e8???????? 83c40c 83ec10 8bcc 51 e8???????? } // n = 7, score = 200 // 68a81606fd | push 0xfd0616a8 // e8???????? | // 83c40c | add esp, 0xc // 83ec10 | sub esp, 0x10 // 8bcc | mov ecx, esp // 51 | push ecx // e8???????? | $sequence_2 = { e8???????? 8b4508 8b5010 8a1a 80fb02 751e 8bca } // n = 7, score = 200 // e8???????? | // 8b4508 | mov eax, dword ptr [ebp + 8] // 8b5010 | mov edx, dword ptr [eax + 0x10] // 8a1a | mov bl, byte ptr [edx] // 80fb02 | cmp bl, 2 // 751e | jne 0x20 // 8bca | mov ecx, edx $sequence_3 = { 72f6 50 8d8ea8000000 e8???????? 8b4dfc 5f 5e } // n = 7, score = 200 // 72f6 | jb 0xfffffff8 // 50 | push eax // 8d8ea8000000 | lea ecx, [esi + 0xa8] // e8???????? | // 8b4dfc | mov ecx, dword ptr [ebp - 4] // 5f | pop edi // 5e | pop esi $sequence_4 = { f7fe 88540dd4 41 83f905 72e3 8d45d4 885dd9 } // n = 7, score = 200 // f7fe | idiv esi // 88540dd4 | mov byte ptr [ebp + ecx - 0x2c], dl // 41 | inc ecx // 83f905 | cmp ecx, 5 // 72e3 | jb 0xffffffe5 // 8d45d4 | lea eax, [ebp - 0x2c] // 885dd9 | mov byte ptr [ebp - 0x27], bl $sequence_5 = { 83c0fd 3bd8 7e99 8b45f4 83f802 752e 8b45fc } // n = 7, score = 200 // 83c0fd | add eax, -3 // 3bd8 | cmp ebx, eax // 7e99 | jle 0xffffff9b // 8b45f4 | mov eax, dword ptr [ebp - 0xc] // 83f802 | cmp eax, 2 // 752e | jne 0x30 // 8b45fc | mov eax, dword ptr [ebp - 4] $sequence_6 = { e8???????? 51 54 8d4d38 e8???????? 8d8d30ffffff } // n = 6, score = 200 // e8???????? | // 51 | push ecx // 54 | push esp // 8d4d38 | lea ecx, [ebp + 0x38] // e8???????? | // 8d8d30ffffff | lea ecx, [ebp - 0xd0] $sequence_7 = { f7fe 88540dd8 41 83f904 72e3 8d45d8 885ddc } // n = 7, score = 200 // f7fe | idiv esi // 88540dd8 | mov byte ptr [ebp + ecx - 0x28], dl // 41 | inc ecx // 83f904 | cmp ecx, 4 // 72e3 | jb 0xffffffe5 // 8d45d8 | lea eax, [ebp - 0x28] // 885ddc | mov byte ptr [ebp - 0x24], bl $sequence_8 = { 68d86e06fd eb41 51 8d4de4 e8???????? 68e46f06fd eb31 } // n = 7, score = 200 // 68d86e06fd | push 0xfd066ed8 // eb41 | jmp 0x43 // 51 | push ecx // 8d4de4 | lea ecx, [ebp - 0x1c] // e8???????? | // 68e46f06fd | push 0xfd066fe4 // eb31 | jmp 0x33 $sequence_9 = { b9c59d1c81 03d6 898d88faffff 8a0a 42 888d83faffff } // n = 6, score = 200 // b9c59d1c81 | mov ecx, 0x811c9dc5 // 03d6 | add edx, esi // 898d88faffff | mov dword ptr [ebp - 0x578], ecx // 8a0a | mov cl, byte ptr [edx] // 42 | inc edx // 888d83faffff | mov byte ptr [ebp - 0x57d], cl condition: 7 of them and filesize < 794624 }
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