Actor(s): GOLD DUPONT
RansomExx is a ransomware family that targeted multiple companies starting in mid-2020. It shares commonalities with Defray777.
rule win_ransomexx_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2022-05-16" version = "1" description = "Detects win.ransomexx." 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.ransomexx" 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 = { 8b443454 8d4c2414 8d9424a8000000 51 89542430 897c2428 8944242c } // n = 7, score = 100 // 8b443454 | mov eax, dword ptr [esp + esi + 0x54] // 8d4c2414 | lea ecx, [esp + 0x14] // 8d9424a8000000 | lea edx, [esp + 0xa8] // 51 | push ecx // 89542430 | mov dword ptr [esp + 0x30], edx // 897c2428 | mov dword ptr [esp + 0x28], edi // 8944242c | mov dword ptr [esp + 0x2c], eax $sequence_1 = { 0f8532040000 03db 8d75d0 e8???????? 8bf0 85f6 0f851e040000 } // n = 7, score = 100 // 0f8532040000 | jne 0x438 // 03db | add ebx, ebx // 8d75d0 | lea esi, [ebp - 0x30] // e8???????? | // 8bf0 | mov esi, eax // 85f6 | test esi, esi // 0f851e040000 | jne 0x424 $sequence_2 = { 51 6a02 52 ffd6 85c0 7405 bb01000000 } // n = 7, score = 100 // 51 | push ecx // 6a02 | push 2 // 52 | push edx // ffd6 | call esi // 85c0 | test eax, eax // 7405 | je 7 // bb01000000 | mov ebx, 1 $sequence_3 = { 0fb6b688614200 c1e108 33ce 338a886a4200 8b7004 3308 8b7808 } // n = 7, score = 100 // 0fb6b688614200 | movzx esi, byte ptr [esi + 0x426188] // c1e108 | shl ecx, 8 // 33ce | xor ecx, esi // 338a886a4200 | xor ecx, dword ptr [edx + 0x426a88] // 8b7004 | mov esi, dword ptr [eax + 4] // 3308 | xor ecx, dword ptr [eax] // 8b7808 | mov edi, dword ptr [eax + 8] $sequence_4 = { 8bfc 85ff 0f8486000000 8bcf 8bf7 8bd7 33c0 } // n = 7, score = 100 // 8bfc | mov edi, esp // 85ff | test edi, edi // 0f8486000000 | je 0x8c // 8bcf | mov ecx, edi // 8bf7 | mov esi, edi // 8bd7 | mov edx, edi // 33c0 | xor eax, eax $sequence_5 = { 50 51 ff15???????? 85c0 7439 8d8dfcfeffff 51 } // n = 7, score = 100 // 50 | push eax // 51 | push ecx // ff15???????? | // 85c0 | test eax, eax // 7439 | je 0x3b // 8d8dfcfeffff | lea ecx, [ebp - 0x104] // 51 | push ecx $sequence_6 = { 7425 3bc8 7321 8b5496fc 33db } // n = 5, score = 100 // 7425 | je 0x27 // 3bc8 | cmp ecx, eax // 7321 | jae 0x23 // 8b5496fc | mov edx, dword ptr [esi + edx*4 - 4] // 33db | xor ebx, ebx $sequence_7 = { ff15???????? 50 ff15???????? 6a00 57 ff15???????? 57 } // n = 7, score = 100 // ff15???????? | // 50 | push eax // ff15???????? | // 6a00 | push 0 // 57 | push edi // ff15???????? | // 57 | push edi $sequence_8 = { 8bfa 337c2448 8bde 335c244c 237c2450 235c2454 33fa } // n = 7, score = 100 // 8bfa | mov edi, edx // 337c2448 | xor edi, dword ptr [esp + 0x48] // 8bde | mov ebx, esi // 335c244c | xor ebx, dword ptr [esp + 0x4c] // 237c2450 | and edi, dword ptr [esp + 0x50] // 235c2454 | and ebx, dword ptr [esp + 0x54] // 33fa | xor edi, edx $sequence_9 = { 83c006 32903fb44100 885406ff 83f824 0f8c59ffffff a1???????? 8b4dec } // n = 7, score = 100 // 83c006 | add eax, 6 // 32903fb44100 | xor dl, byte ptr [eax + 0x41b43f] // 885406ff | mov byte ptr [esi + eax - 1], dl // 83f824 | cmp eax, 0x24 // 0f8c59ffffff | jl 0xffffff5f // a1???????? | // 8b4dec | mov ecx, dword ptr [ebp - 0x14] condition: 7 of them and filesize < 372736 }
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