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 = "2023-12-06" 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 = "20231130" malpedia_hash = "fc8a0e9f343f6d6ded9e7df1a64dac0cc68d7351" malpedia_version = "20230808" 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 = { 8bc3 8d75e0 e8???????? 8bf0 85f6 0f85f8020000 eb07 } // n = 7, score = 100 // 8bc3 | mov eax, ebx // 8d75e0 | lea esi, [ebp - 0x20] // e8???????? | // 8bf0 | mov esi, eax // 85f6 | test esi, esi // 0f85f8020000 | jne 0x2fe // eb07 | jmp 9 $sequence_1 = { 6884010000 6a08 c745fc04010000 ffd7 50 ff15???????? 8bf0 } // n = 7, score = 100 // 6884010000 | push 0x184 // 6a08 | push 8 // c745fc04010000 | mov dword ptr [ebp - 4], 0x104 // ffd7 | call edi // 50 | push eax // ff15???????? | // 8bf0 | mov esi, eax $sequence_2 = { 8b4f08 3bce 7425 8b4704 03c0 03c0 } // n = 6, score = 100 // 8b4f08 | mov ecx, dword ptr [edi + 8] // 3bce | cmp ecx, esi // 7425 | je 0x27 // 8b4704 | mov eax, dword ptr [edi + 4] // 03c0 | add eax, eax // 03c0 | add eax, eax $sequence_3 = { 8bf8 85ff 752c 8d55f8 c70601000000 6a02 } // n = 6, score = 100 // 8bf8 | mov edi, eax // 85ff | test edi, edi // 752c | jne 0x2e // 8d55f8 | lea edx, [ebp - 8] // c70601000000 | mov dword ptr [esi], 1 // 6a02 | push 2 $sequence_4 = { c1ee0a 33fe 8bf7 8b7dfc 039c3da4feffff 03f3 } // n = 6, score = 100 // c1ee0a | shr esi, 0xa // 33fe | xor edi, esi // 8bf7 | mov esi, edi // 8b7dfc | mov edi, dword ptr [ebp - 4] // 039c3da4feffff | add ebx, dword ptr [ebp + edi - 0x15c] // 03f3 | add esi, ebx $sequence_5 = { c1ee03 33fe 03df 8b7dfc 039c3db8feffff 8bb43d94feffff 03f3 } // n = 7, score = 100 // c1ee03 | shr esi, 3 // 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 $sequence_6 = { 837df801 0f8612010000 8b4df8 8b5f04 49 b801000000 d3e0 } // n = 7, score = 100 // 837df801 | cmp dword ptr [ebp - 8], 1 // 0f8612010000 | jbe 0x118 // 8b4df8 | mov ecx, dword ptr [ebp - 8] // 8b5f04 | mov ebx, dword ptr [edi + 4] // 49 | dec ecx // b801000000 | mov eax, 1 // d3e0 | shl eax, cl $sequence_7 = { 8b55f0 8b4508 8d4dd0 51 52 57 50 } // n = 7, score = 100 // 8b55f0 | mov edx, dword ptr [ebp - 0x10] // 8b4508 | mov eax, dword ptr [ebp + 8] // 8d4dd0 | lea ecx, [ebp - 0x30] // 51 | push ecx // 52 | push edx // 57 | push edi // 50 | push eax $sequence_8 = { 56 50 e8???????? 8b07 83c40c 8975fc } // n = 6, score = 100 // 56 | push esi // 50 | push eax // e8???????? | // 8b07 | mov eax, dword ptr [edi] // 83c40c | add esp, 0xc // 8975fc | mov dword ptr [ebp - 4], esi $sequence_9 = { 39742420 0f862e010000 8d642400 837c242001 7540 837c242400 7539 } // n = 7, score = 100 // 39742420 | cmp dword ptr [esp + 0x20], esi // 0f862e010000 | jbe 0x134 // 8d642400 | lea esp, [esp] // 837c242001 | cmp dword ptr [esp + 0x20], 1 // 7540 | jne 0x42 // 837c242400 | cmp dword ptr [esp + 0x24], 0 // 7539 | jne 0x3b condition: 7 of them and filesize < 372736 }
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