Ransomware
rule win_sfile_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2026-01-05" 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 = "20260105" malpedia_hash = "19b79e7cab4eaf532122e5b45a77dd8f6bb5cc79" malpedia_version = "20251219" 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 = { 52 8b4514 50 e8???????? 83c408 eb49 } // n = 6, score = 300 // 52 | push edx // 8b4514 | mov eax, dword ptr [ebp + 0x14] // 50 | push eax // e8???????? | // 83c408 | add esp, 8 // eb49 | jmp 0x4b $sequence_1 = { 8b55f8 2b55e8 d1fa 8955e4 8b45e4 } // n = 5, score = 300 // 8b55f8 | mov edx, dword ptr [ebp - 8] // 2b55e8 | sub edx, dword ptr [ebp - 0x18] // d1fa | sar edx, 1 // 8955e4 | mov dword ptr [ebp - 0x1c], edx // 8b45e4 | mov eax, dword ptr [ebp - 0x1c] $sequence_2 = { 8b55fc c7422000000000 8d45fc 50 } // n = 4, score = 300 // 8b55fc | mov edx, dword ptr [ebp - 4] // c7422000000000 | mov dword ptr [edx + 0x20], 0 // 8d45fc | lea eax, [ebp - 4] // 50 | push eax $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 = { 8b4818 51 ff15???????? 8b55fc 8b421c } // n = 5, score = 300 // 8b4818 | mov ecx, dword ptr [eax + 0x18] // 51 | push ecx // ff15???????? | // 8b55fc | mov edx, dword ptr [ebp - 4] // 8b421c | mov eax, dword ptr [edx + 0x1c] $sequence_5 = { 8d8db8fdffff 51 e8???????? 83c41c 837dc800 7507 } // n = 6, score = 300 // 8d8db8fdffff | lea ecx, [ebp - 0x248] // 51 | push ecx // e8???????? | // 83c41c | add esp, 0x1c // 837dc800 | cmp dword ptr [ebp - 0x38], 0 // 7507 | jne 9 $sequence_6 = { 8b4244 8b4d08 8b5120 8b4008 } // n = 4, score = 300 // 8b4244 | mov eax, dword ptr [edx + 0x44] // 8b4d08 | mov ecx, dword ptr [ebp + 8] // 8b5120 | mov edx, dword ptr [ecx + 0x20] // 8b4008 | mov eax, dword ptr [eax + 8] $sequence_7 = { 8b5158 52 e8???????? 83c404 8b4510 } // n = 5, score = 300 // 8b5158 | mov edx, dword ptr [ecx + 0x58] // 52 | push edx // e8???????? | // 83c404 | add esp, 4 // 8b4510 | mov eax, dword ptr [ebp + 0x10] $sequence_8 = { 8b751c 8b4d20 f3a4 837d0802 } // n = 4, score = 300 // 8b751c | mov esi, dword ptr [ebp + 0x1c] // 8b4d20 | mov ecx, dword ptr [ebp + 0x20] // f3a4 | rep movsb byte ptr es:[edi], byte ptr [esi] // 837d0802 | cmp dword ptr [ebp + 8], 2 $sequence_9 = { 8bec 83ec2c 56 57 c745f400000000 } // n = 5, score = 300 // 8bec | mov ebp, esp // 83ec2c | sub esp, 0x2c // 56 | push esi // 57 | push edi // c745f400000000 | mov dword ptr [ebp - 0xc], 0 condition: 7 of them and filesize < 588800 }
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