Ransomware. Uses dropper written in JavaScript to deploy a .NET payload.
rule win_blackbyte_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-01-25" version = "1" description = "Detects win.blackbyte." 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.blackbyte" 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 = { 488b442418 488b5c2410 e8???????? 488b4c2420 488b01 440f117c2428 488d5c2428 } // n = 7, score = 200 // 488b442418 | mov byte ptr [esp + 0x53], ch // 488b5c2410 | inc esp // e8???????? | // 488b4c2420 | movzx ebp, byte ptr [esp + 0x64] // 488b01 | inc esp // 440f117c2428 | mov byte ptr [esp + 0x52], ch // 488d5c2428 | inc esp $sequence_1 = { e8???????? 4889442460 48895c2428 e8???????? 440f117c2470 4889442470 48895c2478 } // n = 7, score = 200 // e8???????? | // 4889442460 | mov byte ptr [eax], 0x7a // 48895c2428 | dec eax // e8???????? | // 440f117c2470 | lea eax, [0x3dfac] // 4889442470 | dec eax // 48895c2478 | lea ebp, [esp + 0x30] $sequence_2 = { 488d7101 488935???????? 48c1e104 48895c0a08 488d3c0a 833d????????00 7507 } // n = 7, score = 200 // 488d7101 | xor edx, edx // 488935???????? | // 48c1e104 | xor ebx, ebx // 48895c0a08 | dec eax // 488d3c0a | mov dword ptr [esp + 0x60], ebp // 833d????????00 | // 7507 | dec eax $sequence_3 = { 735c 0fb6740433 89d7 31f2 01c2 4883ff15 } // n = 6, score = 200 // 735c | mov dword ptr [esp + 0x68], eax // 0fb6740433 | dec eax // 89d7 | lea eax, [0x123825] // 31f2 | dec eax // 01c2 | mov ecx, ebx // 4883ff15 | dec eax $sequence_4 = { 4881c490000000 c3 31c0 4889d9 e8???????? 90 4889442408 } // n = 7, score = 200 // 4881c490000000 | movzx edx, byte ptr [esp + 0x57] // c3 | inc esp // 31c0 | add edx, eax // 4889d9 | mov byte ptr [eax + 0xe], dl // e8???????? | // 90 | movzx edx, byte ptr [esp + 0x5d] // 4889442408 | inc esp $sequence_5 = { 488d7818 488b4c2460 e8???????? 488b4c2420 48894810 833d????????00 7512 } // n = 7, score = 200 // 488d7818 | dec eax // 488b4c2460 | shl ecx, 4 // e8???????? | // 488b4c2420 | dec eax // 48894810 | lea ebx, [0x192f35] // 833d????????00 | // 7512 | dec eax $sequence_6 = { 488b542450 488b5c2448 4889c7 4889ce 488b442440 c6041f66 b902000000 } // n = 7, score = 200 // 488b542450 | inc esp // 488b5c2448 | movzx ebp, byte ptr [esp + 0xc6] // 4889c7 | inc esp // 4889ce | mov byte ptr [esp + 0x7d], ch // 488b442440 | inc esp // c6041f66 | movzx ebp, byte ptr [esp + 0xc7] // b902000000 | inc esp $sequence_7 = { 7534 4889442418 48c744242000000000 488d7c2428 488d7ff0 48896c24f0 488d6c24f0 } // n = 7, score = 200 // 7534 | mov byte ptr [edi + ebx], 0xe9 // 4889442418 | mov ecx, 2 // 48c744242000000000 | dec eax // 488d7c2428 | mov ebx, dword ptr [esp + 0x48] // 488d7ff0 | dec eax // 48896c24f0 | mov edi, eax // 488d6c24f0 | dec eax $sequence_8 = { e8???????? 0f1f00 4885c0 0f85d0000000 488b542460 488b5220 488b4218 } // n = 7, score = 200 // e8???????? | // 0f1f00 | ret // 4885c0 | dec esp // 0f85d0000000 | mov edx, dword ptr [esp + 0x128] // 488b542460 | dec eax // 488b5220 | lea edi, [0x1f78cf] // 488b4218 | movzx ebx, word ptr [edi + ebx*2] $sequence_9 = { 488d5c241a b906000000 e8???????? 488b6c2428 4883c430 c3 89f0 } // n = 7, score = 200 // 488d5c241a | dec eax // b906000000 | mov dword ptr [esp + 0x38], ebx // e8???????? | // 488b6c2428 | dec eax // 4883c430 | lea eax, [0x24ddf9] // c3 | mov ebx, 4 // 89f0 | dec eax condition: 7 of them and filesize < 9435136 }
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