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rule win_fobber_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2026-01-05" version = "1" description = "Detects win.fobber." 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.fobber" 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 = { 8b750c 8b4d10 39f7 760e } // n = 4, score = 1100 // 8b750c | mov esi, dword ptr [ebp + 0xc] // 8b4d10 | mov ecx, dword ptr [ebp + 0x10] // 39f7 | cmp edi, esi // 760e | jbe 0x10 $sequence_1 = { 57 51 8b7d08 30c0 31c9 f7d1 } // n = 6, score = 1100 // 57 | push edi // 51 | push ecx // 8b7d08 | mov edi, dword ptr [ebp + 8] // 30c0 | xor al, al // 31c9 | xor ecx, ecx // f7d1 | not ecx $sequence_2 = { 8d0431 39f8 7607 49 01cf } // n = 5, score = 1100 // 8d0431 | lea eax, [ecx + esi] // 39f8 | cmp eax, edi // 7607 | jbe 9 // 49 | dec ecx // 01cf | add edi, ecx $sequence_3 = { 57 e8???????? 85c0 740f 89c1 } // n = 5, score = 1100 // 57 | push edi // e8???????? | // 85c0 | test eax, eax // 740f | je 0x11 // 89c1 | mov ecx, eax $sequence_4 = { 8d4d08 51 ff31 ffd0 } // n = 4, score = 1100 // 8d4d08 | lea ecx, [ebp + 8] // 51 | push ecx // ff31 | push dword ptr [ecx] // ffd0 | call eax $sequence_5 = { 55 89e5 ff750c 6800300000 } // n = 4, score = 1100 // 55 | push ebp // 89e5 | mov ebp, esp // ff750c | push dword ptr [ebp + 0xc] // 6800300000 | push 0x3000 $sequence_6 = { 0453 42 e2f6 59 } // n = 4, score = 1100 // 0453 | add al, 0x53 // 42 | inc edx // e2f6 | loop 0xfffffff8 // 59 | pop ecx $sequence_7 = { f2ae 31c0 e303 4f } // n = 4, score = 1100 // f2ae | repne scasb al, byte ptr es:[edi] // 31c0 | xor eax, eax // e303 | jecxz 5 // 4f | dec edi $sequence_8 = { 8981efc00700 0081efe82300 0081c7371300 0081c7546900 0081c7397d00 00e9 } // n = 6, score = 100 // 8981efc00700 | mov dword ptr [ecx + 0x7c0ef], eax // 0081efe82300 | add byte ptr [ecx + 0x23e8ef], al // 0081c7371300 | add byte ptr [ecx + 0x1337c7], al // 0081c7546900 | add byte ptr [ecx + 0x6954c7], al // 0081c7397d00 | add byte ptr [ecx + 0x7d39c7], al // 00e9 | add cl, ch $sequence_9 = { 0f85196e0100 807dfc00 7407 8b4df8 836170fd 5e } // n = 6, score = 100 // 0f85196e0100 | jne 0x16e1f // 807dfc00 | cmp byte ptr [ebp - 4], 0 // 7407 | je 9 // 8b4df8 | mov ecx, dword ptr [ebp - 8] // 836170fd | and dword ptr [ecx + 0x70], 0xfffffffd // 5e | pop esi $sequence_10 = { 4d fc 02e9 5a a2???????? 92 b4ff } // n = 7, score = 100 // 4d | dec ebp // fc | cld // 02e9 | add ch, cl // 5a | pop edx // a2???????? | // 92 | xchg eax, edx // b4ff | mov ah, 0xff $sequence_11 = { 0f8423050000 ff7508 e8???????? 59 59 8b4508 } // n = 6, score = 100 // 0f8423050000 | je 0x529 // ff7508 | push dword ptr [ebp + 8] // e8???????? | // 59 | pop ecx // 59 | pop ecx // 8b4508 | mov eax, dword ptr [ebp + 8] $sequence_12 = { 43 7706 6205???????? 294a75 f2149c } // n = 5, score = 100 // 43 | inc ebx // 7706 | ja 8 // 6205???????? | // 294a75 | sub dword ptr [edx + 0x75], ecx // f2149c | adc al, 0x9c $sequence_13 = { 6a52 686bb7ade9 e8???????? 83c408 } // n = 4, score = 100 // 6a52 | push 0x52 // 686bb7ade9 | push 0xe9adb76b // e8???????? | // 83c408 | add esp, 8 $sequence_14 = { 3bc3 7524 8b451c 3bc3 } // n = 4, score = 100 // 3bc3 | cmp eax, ebx // 7524 | jne 0x26 // 8b451c | mov eax, dword ptr [ebp + 0x1c] // 3bc3 | cmp eax, ebx $sequence_15 = { 33db 57 3bcb 0f8499840100 3bf3 0f84a2840100 } // n = 6, score = 100 // 33db | xor ebx, ebx // 57 | push edi // 3bcb | cmp ecx, ebx // 0f8499840100 | je 0x1849f // 3bf3 | cmp esi, ebx // 0f84a2840100 | je 0x184a8 condition: 7 of them and filesize < 188416 }
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