Ransomware.
rule win_mrdec_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2022-05-16" version = "1" description = "Detects win.mrdec." 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.mrdec" 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 = { 8b45e4 c1e005 0345ec 83780c01 } // n = 4, score = 100 // 8b45e4 | mov eax, dword ptr [ebp - 0x1c] // c1e005 | shl eax, 5 // 0345ec | add eax, dword ptr [ebp - 0x14] // 83780c01 | cmp dword ptr [eax + 0xc], 1 $sequence_1 = { 8d45f8 50 6800010000 8d85e4feffff 50 ff75fc } // n = 6, score = 100 // 8d45f8 | lea eax, [ebp - 8] // 50 | push eax // 6800010000 | push 0x100 // 8d85e4feffff | lea eax, [ebp - 0x11c] // 50 | push eax // ff75fc | push dword ptr [ebp - 4] $sequence_2 = { ff75e4 e8???????? 6a00 ff75d8 e8???????? 68000000f0 6a01 } // n = 7, score = 100 // ff75e4 | push dword ptr [ebp - 0x1c] // e8???????? | // 6a00 | push 0 // ff75d8 | push dword ptr [ebp - 0x28] // e8???????? | // 68000000f0 | push 0xf0000000 // 6a01 | push 1 $sequence_3 = { e8???????? c64446fa00 57 56 e8???????? 68???????? 56 } // n = 7, score = 100 // e8???????? | // c64446fa00 | mov byte ptr [esi + eax*2 - 6], 0 // 57 | push edi // 56 | push esi // e8???????? | // 68???????? | // 56 | push esi $sequence_4 = { f3a4 0345fc c7005c2a2e2a c6400400 6860800100 e8???????? } // n = 6, score = 100 // f3a4 | rep movsb byte ptr es:[edi], byte ptr [esi] // 0345fc | add eax, dword ptr [ebp - 4] // c7005c2a2e2a | mov dword ptr [eax], 0x2a2e2a5c // c6400400 | mov byte ptr [eax + 4], 0 // 6860800100 | push 0x18060 // e8???????? | $sequence_5 = { ff75dc 68???????? e8???????? 6a00 6a00 68???????? } // n = 6, score = 100 // ff75dc | push dword ptr [ebp - 0x24] // 68???????? | // e8???????? | // 6a00 | push 0 // 6a00 | push 0 // 68???????? | $sequence_6 = { fc f3a4 0345fc c7005c2a2e2a c6400400 6860800100 } // n = 6, score = 100 // fc | cld // f3a4 | rep movsb byte ptr es:[edi], byte ptr [esi] // 0345fc | add eax, dword ptr [ebp - 4] // c7005c2a2e2a | mov dword ptr [eax], 0x2a2e2a5c // c6400400 | mov byte ptr [eax + 4], 0 // 6860800100 | push 0x18060 $sequence_7 = { ff75e0 e8???????? 3dea000000 752d ff75ec e8???????? } // n = 6, score = 100 // ff75e0 | push dword ptr [ebp - 0x20] // e8???????? | // 3dea000000 | cmp eax, 0xea // 752d | jne 0x2f // ff75ec | push dword ptr [ebp - 0x14] // e8???????? | $sequence_8 = { 50 e8???????? 83f8ff 7526 8b4508 8bc8 } // n = 6, score = 100 // 50 | push eax // e8???????? | // 83f8ff | cmp eax, -1 // 7526 | jne 0x28 // 8b4508 | mov eax, dword ptr [ebp + 8] // 8bc8 | mov ecx, eax $sequence_9 = { 68???????? e8???????? 85c0 0f84a4010000 } // n = 4, score = 100 // 68???????? | // e8???????? | // 85c0 | test eax, eax // 0f84a4010000 | je 0x1aa condition: 7 of them and filesize < 44864 }
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