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 = "2023-01-25" 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 = "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 = { 897704 897708 8d7b38 3bfe 7439 8b4f08 3bce } // n = 7, score = 100 // 897704 | mov dword ptr [edi + 4], esi // 897708 | mov dword ptr [edi + 8], esi // 8d7b38 | lea edi, [ebx + 0x38] // 3bfe | cmp edi, esi // 7439 | je 0x3b // 8b4f08 | mov ecx, dword ptr [edi + 8] // 3bce | cmp ecx, esi $sequence_1 = { 333c9db07e4200 8945fc 895508 3330 83c004 8945fc 8975dc } // n = 7, score = 100 // 333c9db07e4200 | xor edi, dword ptr [ebx*4 + 0x427eb0] // 8945fc | mov dword ptr [ebp - 4], eax // 895508 | mov dword ptr [ebp + 8], edx // 3330 | xor esi, dword ptr [eax] // 83c004 | add eax, 4 // 8945fc | mov dword ptr [ebp - 4], eax // 8975dc | mov dword ptr [ebp - 0x24], esi $sequence_2 = { 41 00745b41 009c5b41008a46 0323 } // n = 4, score = 100 // 41 | inc ecx // 00745b41 | add byte ptr [ebx + ebx*2 + 0x41], dh // 009c5b41008a46 | add byte ptr [ebx + ebx*2 + 0x468a0041], bl // 0323 | add esp, dword ptr [ebx] $sequence_3 = { 338a886a4200 8b7004 3308 8b7808 33f1 894810 33fe } // n = 7, score = 100 // 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] // 33f1 | xor esi, ecx // 894810 | mov dword ptr [eax + 0x10], ecx // 33fe | xor edi, esi $sequence_4 = { 8d442408 e8???????? 8bf0 85f6 7525 8b4d0c 8b5508 } // n = 7, score = 100 // 8d442408 | lea eax, [esp + 8] // e8???????? | // 8bf0 | mov esi, eax // 85f6 | test esi, esi // 7525 | jne 0x27 // 8b4d0c | mov ecx, dword ptr [ebp + 0xc] // 8b5508 | mov edx, dword ptr [ebp + 8] $sequence_5 = { 0fb6701e 0fb6b688614200 c1e108 33ce 0fb6701d 0fb6b688614200 c1e108 } // n = 7, score = 100 // 0fb6701e | movzx esi, byte ptr [eax + 0x1e] // 0fb6b688614200 | movzx esi, byte ptr [esi + 0x426188] // c1e108 | shl ecx, 8 // 33ce | xor ecx, esi // 0fb6701d | movzx esi, byte ptr [eax + 0x1d] // 0fb6b688614200 | movzx esi, byte ptr [esi + 0x426188] // c1e108 | shl ecx, 8 $sequence_6 = { 8d48bf 80f905 7706 0fbed0 83ea37 8d489f 80f905 } // n = 7, score = 100 // 8d48bf | lea ecx, [eax - 0x41] // 80f905 | cmp cl, 5 // 7706 | ja 8 // 0fbed0 | movsx edx, al // 83ea37 | sub edx, 0x37 // 8d489f | lea ecx, [eax - 0x61] // 80f905 | cmp cl, 5 $sequence_7 = { c3 8bff 55 8bec 8b4508 33c9 3b04cd60304200 } // n = 7, score = 100 // c3 | ret // 8bff | mov edi, edi // 55 | push ebp // 8bec | mov ebp, esp // 8b4508 | mov eax, dword ptr [ebp + 8] // 33c9 | xor ecx, ecx // 3b04cd60304200 | cmp eax, dword ptr [ecx*8 + 0x423060] $sequence_8 = { 6a00 ff15???????? 8b1d???????? 57 6a00 6a01 ffd3 } // n = 7, score = 100 // 6a00 | push 0 // ff15???????? | // 8b1d???????? | // 57 | push edi // 6a00 | push 0 // 6a01 | push 1 // ffd3 | call ebx $sequence_9 = { 8b542408 f30f6f09 f30f7f0a 660f6fd1 8d0530304200 660f6f00 8d0500304200 } // n = 7, score = 100 // 8b542408 | mov edx, dword ptr [esp + 8] // f30f6f09 | movdqu xmm1, xmmword ptr [ecx] // f30f7f0a | movdqu xmmword ptr [edx], xmm1 // 660f6fd1 | movdqa xmm2, xmm1 // 8d0530304200 | lea eax, [0x423030] // 660f6f00 | movdqa xmm0, xmmword ptr [eax] // 8d0500304200 | lea eax, [0x423000] condition: 7 of them and filesize < 372736 }
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