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 = "2023-07-11" 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 = "20230705" malpedia_hash = "42d0574f4405bd7d2b154d321d345acb18834a41" malpedia_version = "20230715" 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 = { 33fe 03df 8b7dfc 039c3db8feffff 8bb43d94feffff 03f3 89b43dd4feffff } // n = 7, score = 100 // 33fe | xor edi, esi // 03df | add ebx, edi // 8b7dfc | mov edi, dword ptr [ebp - 4] // 039c3db8feffff | add ebx, dword ptr [ebp + edi - 0x148] // 8bb43d94feffff | mov esi, dword ptr [ebp + edi - 0x16c] // 03f3 | add esi, ebx // 89b43dd4feffff | mov dword ptr [ebp + edi - 0x12c], esi $sequence_1 = { 03442418 8b54240c 134c241c 0302 134a04 01442450 89442458 } // n = 7, score = 100 // 03442418 | add eax, dword ptr [esp + 0x18] // 8b54240c | mov edx, dword ptr [esp + 0xc] // 134c241c | adc ecx, dword ptr [esp + 0x1c] // 0302 | add eax, dword ptr [edx] // 134a04 | adc ecx, dword ptr [edx + 4] // 01442450 | add dword ptr [esp + 0x50], eax // 89442458 | mov dword ptr [esp + 0x58], eax $sequence_2 = { 0fb6b688614200 c1e708 33f7 8b7d08 83c004 c1e608 8955ec } // n = 7, score = 100 // 0fb6b688614200 | movzx esi, byte ptr [esi + 0x426188] // c1e708 | shl edi, 8 // 33f7 | xor esi, edi // 8b7d08 | mov edi, dword ptr [ebp + 8] // 83c004 | add eax, 4 // c1e608 | shl esi, 8 // 8955ec | mov dword ptr [ebp - 0x14], edx $sequence_3 = { c1e008 0bc3 41 4e 75f4 } // n = 5, score = 100 // c1e008 | shl eax, 8 // 0bc3 | or eax, ebx // 41 | inc ecx // 4e | dec esi // 75f4 | jne 0xfffffff6 $sequence_4 = { e8???????? 83c410 6a00 ff15???????? 50 ff15???????? 8b35???????? } // n = 7, score = 100 // e8???????? | // 83c410 | add esp, 0x10 // 6a00 | push 0 // ff15???????? | // 50 | push eax // ff15???????? | // 8b35???????? | $sequence_5 = { 85f6 0f84b1000000 395d08 0f84a8000000 395d0c 0f849f000000 68000000f0 } // n = 7, score = 100 // 85f6 | test esi, esi // 0f84b1000000 | je 0xb7 // 395d08 | cmp dword ptr [ebp + 8], ebx // 0f84a8000000 | je 0xae // 395d0c | cmp dword ptr [ebp + 0xc], ebx // 0f849f000000 | je 0xa5 // 68000000f0 | push 0xf0000000 $sequence_6 = { 830d????????01 8d4310 e8???????? 8bcc 3bcb 0f84e8000000 8bd1 } // n = 7, score = 100 // 830d????????01 | // 8d4310 | lea eax, [ebx + 0x10] // e8???????? | // 8bcc | mov ecx, esp // 3bcb | cmp ecx, ebx // 0f84e8000000 | je 0xee // 8bd1 | mov edx, ecx $sequence_7 = { 7477 817dec00020000 756e b900020000 } // n = 4, score = 100 // 7477 | je 0x79 // 817dec00020000 | cmp dword ptr [ebp - 0x14], 0x200 // 756e | jne 0x70 // b900020000 | mov ecx, 0x200 $sequence_8 = { 8d45cc bb01000000 898574ffffff 8d856cffffff 8bcf 8955cc } // n = 6, score = 100 // 8d45cc | lea eax, [ebp - 0x34] // bb01000000 | mov ebx, 1 // 898574ffffff | mov dword ptr [ebp - 0x8c], eax // 8d856cffffff | lea eax, [ebp - 0x94] // 8bcf | mov ecx, edi // 8955cc | mov dword ptr [ebp - 0x34], edx $sequence_9 = { e8???????? 8bf0 83c414 85f6 7567 8b45fc 40 } // n = 7, score = 100 // e8???????? | // 8bf0 | mov esi, eax // 83c414 | add esp, 0x14 // 85f6 | test esi, esi // 7567 | jne 0x69 // 8b45fc | mov eax, dword ptr [ebp - 4] // 40 | inc eax condition: 7 of them and filesize < 372736 }
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