Actor(s): Lazarus Group
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rule win_wannacryptor_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-03-28" version = "1" description = "Detects win.wannacryptor." 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.wannacryptor" malpedia_rule_date = "20230328" malpedia_hash = "9d2d75cef573c1c2d861f5197df8f563b05a305d" malpedia_version = "20230407" 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 = { 83ec1c 56 8bf1 8a465a 84c0 756f 8a4658 } // n = 7, score = 600 // 83ec1c | sub esp, 0x1c // 56 | push esi // 8bf1 | mov esi, ecx // 8a465a | mov al, byte ptr [esi + 0x5a] // 84c0 | test al, al // 756f | jne 0x71 // 8a4658 | mov al, byte ptr [esi + 0x58] $sequence_1 = { c20c00 8bce e8???????? 84c0 } // n = 4, score = 600 // c20c00 | ret 0xc // 8bce | mov ecx, esi // e8???????? | // 84c0 | test al, al $sequence_2 = { 7413 3c2f 7404 3c5c 7503 8d6e01 8a4601 } // n = 7, score = 600 // 7413 | je 0x15 // 3c2f | cmp al, 0x2f // 7404 | je 6 // 3c5c | cmp al, 0x5c // 7503 | jne 5 // 8d6e01 | lea ebp, [esi + 1] // 8a4601 | mov al, byte ptr [esi + 1] $sequence_3 = { 8b7c241c 85ff 7409 57 e8???????? 83c404 8b442420 } // n = 7, score = 600 // 8b7c241c | mov edi, dword ptr [esp + 0x1c] // 85ff | test edi, edi // 7409 | je 0xb // 57 | push edi // e8???????? | // 83c404 | add esp, 4 // 8b442420 | mov eax, dword ptr [esp + 0x20] $sequence_4 = { b907000000 f3a5 66a5 a4 5f } // n = 5, score = 600 // b907000000 | mov ecx, 7 // f3a5 | rep movsd dword ptr es:[edi], dword ptr [esi] // 66a5 | movsw word ptr es:[edi], word ptr [esi] // a4 | movsb byte ptr es:[edi], byte ptr [esi] // 5f | pop edi $sequence_5 = { 8975dc 83feff 750a 50 8d55f0 52 } // n = 6, score = 600 // 8975dc | mov dword ptr [ebp - 0x24], esi // 83feff | cmp esi, -1 // 750a | jne 0xc // 50 | push eax // 8d55f0 | lea edx, [ebp - 0x10] // 52 | push edx $sequence_6 = { 83e103 f3a4 8b8c2424010000 8bd1 c1fa08 } // n = 5, score = 600 // 83e103 | and ecx, 3 // f3a4 | rep movsb byte ptr es:[edi], byte ptr [esi] // 8b8c2424010000 | mov ecx, dword ptr [esp + 0x124] // 8bd1 | mov edx, ecx // c1fa08 | sar edx, 8 $sequence_7 = { 8bf8 83c9ff 33c0 f2ae f7d1 2bf9 8bc3 } // n = 7, score = 600 // 8bf8 | mov edi, eax // 83c9ff | or ecx, 0xffffffff // 33c0 | xor eax, eax // f2ae | repne scasb al, byte ptr es:[edi] // f7d1 | not ecx // 2bf9 | sub edi, ecx // 8bc3 | mov eax, ebx $sequence_8 = { 57 8bbc2460030000 8bd9 83ff03 7424 83ff02 } // n = 6, score = 600 // 57 | push edi // 8bbc2460030000 | mov edi, dword ptr [esp + 0x360] // 8bd9 | mov ebx, ecx // 83ff03 | cmp edi, 3 // 7424 | je 0x26 // 83ff02 | cmp edi, 2 $sequence_9 = { c744244817406700 894c244c 896c2450 89542454 e8???????? 8b5658 8b4008 } // n = 7, score = 600 // c744244817406700 | mov dword ptr [esp + 0x48], 0x674017 // 894c244c | mov dword ptr [esp + 0x4c], ecx // 896c2450 | mov dword ptr [esp + 0x50], ebp // 89542454 | mov dword ptr [esp + 0x54], edx // e8???????? | // 8b5658 | mov edx, dword ptr [esi + 0x58] // 8b4008 | mov eax, dword ptr [eax + 8] condition: 7 of them and filesize < 540672 }
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