Ransomware
rule win_sfile_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-07-11" version = "1" description = "Detects win.sfile." 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.sfile" 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 = { c745e800000000 8b45e4 50 ff15???????? } // n = 4, score = 300 // c745e800000000 | mov dword ptr [ebp - 0x18], 0 // 8b45e4 | mov eax, dword ptr [ebp - 0x1c] // 50 | push eax // ff15???????? | $sequence_1 = { 8b485c 51 8b55fc 8b4204 } // n = 4, score = 300 // 8b485c | mov ecx, dword ptr [eax + 0x5c] // 51 | push ecx // 8b55fc | mov edx, dword ptr [ebp - 4] // 8b4204 | mov eax, dword ptr [edx + 4] $sequence_2 = { 740d 8b55f8 8b4258 50 ff15???????? 8b4df8 8b5134 } // n = 7, score = 300 // 740d | je 0xf // 8b55f8 | mov edx, dword ptr [ebp - 8] // 8b4258 | mov eax, dword ptr [edx + 0x58] // 50 | push eax // ff15???????? | // 8b4df8 | mov ecx, dword ptr [ebp - 8] // 8b5134 | mov edx, dword ptr [ecx + 0x34] $sequence_3 = { 7433 6aff 8b4dfc 8b5118 52 } // n = 5, score = 300 // 7433 | je 0x35 // 6aff | push -1 // 8b4dfc | mov ecx, dword ptr [ebp - 4] // 8b5118 | mov edx, dword ptr [ecx + 0x18] // 52 | push edx $sequence_4 = { 894140 8b55f8 8b828c050000 50 e8???????? 8b4df8 51 } // n = 7, score = 300 // 894140 | mov dword ptr [ecx + 0x40], eax // 8b55f8 | mov edx, dword ptr [ebp - 8] // 8b828c050000 | mov eax, dword ptr [edx + 0x58c] // 50 | push eax // e8???????? | // 8b4df8 | mov ecx, dword ptr [ebp - 8] // 51 | push ecx $sequence_5 = { 83f810 7309 c745f410000000 eb10 8b4df8 8d148d10000000 } // n = 6, score = 300 // 83f810 | cmp eax, 0x10 // 7309 | jae 0xb // c745f410000000 | mov dword ptr [ebp - 0xc], 0x10 // eb10 | jmp 0x12 // 8b4df8 | mov ecx, dword ptr [ebp - 8] // 8d148d10000000 | lea edx, [ecx*4 + 0x10] $sequence_6 = { 7527 6a10 8b5510 52 } // n = 4, score = 300 // 7527 | jne 0x29 // 6a10 | push 0x10 // 8b5510 | mov edx, dword ptr [ebp + 0x10] // 52 | push edx $sequence_7 = { 51 e8???????? 83c408 eb13 8d95e4fdffff } // n = 5, score = 300 // 51 | push ecx // e8???????? | // 83c408 | add esp, 8 // eb13 | jmp 0x15 // 8d95e4fdffff | lea edx, [ebp - 0x21c] $sequence_8 = { 8b45e8 8b4df8 8b511c 8910 } // n = 4, score = 300 // 8b45e8 | mov eax, dword ptr [ebp - 0x18] // 8b4df8 | mov ecx, dword ptr [ebp - 8] // 8b511c | mov edx, dword ptr [ecx + 0x1c] // 8910 | mov dword ptr [eax], edx $sequence_9 = { ff15???????? 8b55f0 52 ff15???????? 8b45ec } // n = 5, score = 300 // ff15???????? | // 8b55f0 | mov edx, dword ptr [ebp - 0x10] // 52 | push edx // ff15???????? | // 8b45ec | mov eax, dword ptr [ebp - 0x14] condition: 7 of them and filesize < 588800 }
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