Actor(s): NARWHAL SPIDER
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rule win_cutwail_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2020-12-22" version = "1" description = "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.cutwail" malpedia_rule_date = "20201222" malpedia_hash = "30354d830a29f0fbd3714d93d94dea941d77a130" malpedia_version = "20201023" 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 = { 85c0 7403 c60000 53 6800040000 bb???????? } // n = 6, score = 100 // 85c0 | test eax, eax // 7403 | je 5 // c60000 | mov byte ptr [eax], 0 // 53 | push ebx // 6800040000 | push 0x400 // bb???????? | $sequence_1 = { ff30 e8???????? e8???????? 8b06 ff30 } // n = 5, score = 100 // ff30 | push dword ptr [eax] // e8???????? | // e8???????? | // 8b06 | mov eax, dword ptr [esi] // ff30 | push dword ptr [eax] $sequence_2 = { 83bdf0fdffff46 0f8d23010000 6800020000 6a00 } // n = 4, score = 100 // 83bdf0fdffff46 | cmp dword ptr [ebp - 0x210], 0x46 // 0f8d23010000 | jge 0x129 // 6800020000 | push 0x200 // 6a00 | push 0 $sequence_3 = { 8b7d10 3bfb 746b 8b4508 33c9 6a04 } // n = 6, score = 100 // 8b7d10 | mov edi, dword ptr [ebp + 0x10] // 3bfb | cmp edi, ebx // 746b | je 0x6d // 8b4508 | mov eax, dword ptr [ebp + 8] // 33c9 | xor ecx, ecx // 6a04 | push 4 $sequence_4 = { f775f4 8955d8 e8???????? 33d2 f775e4 8955dc } // n = 6, score = 100 // f775f4 | div dword ptr [ebp - 0xc] // 8955d8 | mov dword ptr [ebp - 0x28], edx // e8???????? | // 33d2 | xor edx, edx // f775e4 | div dword ptr [ebp - 0x1c] // 8955dc | mov dword ptr [ebp - 0x24], edx $sequence_5 = { 0f84b3030000 48 0f846af9ffff 48 0f84c5faffff } // n = 5, score = 100 // 0f84b3030000 | je 0x3b9 // 48 | dec eax // 0f846af9ffff | je 0xfffff970 // 48 | dec eax // 0f84c5faffff | je 0xfffffacb $sequence_6 = { 2b45f8 894510 eb9a 837d1400 7408 8b4d14 } // n = 6, score = 100 // 2b45f8 | sub eax, dword ptr [ebp - 8] // 894510 | mov dword ptr [ebp + 0x10], eax // eb9a | jmp 0xffffff9c // 837d1400 | cmp dword ptr [ebp + 0x14], 0 // 7408 | je 0xa // 8b4d14 | mov ecx, dword ptr [ebp + 0x14] $sequence_7 = { 56 57 8b7c240c 8b07 8b4804 33f6 2bce } // n = 7, score = 100 // 56 | push esi // 57 | push edi // 8b7c240c | mov edi, dword ptr [esp + 0xc] // 8b07 | mov eax, dword ptr [edi] // 8b4804 | mov ecx, dword ptr [eax + 4] // 33f6 | xor esi, esi // 2bce | sub ecx, esi $sequence_8 = { 8b442410 85c0 740f 894629 894e10 c7461801000000 eb07 } // n = 7, score = 100 // 8b442410 | mov eax, dword ptr [esp + 0x10] // 85c0 | test eax, eax // 740f | je 0x11 // 894629 | mov dword ptr [esi + 0x29], eax // 894e10 | mov dword ptr [esi + 0x10], ecx // c7461801000000 | mov dword ptr [esi + 0x18], 1 // eb07 | jmp 9 $sequence_9 = { eb0d 6a01 ff15???????? e9???????? } // n = 4, score = 100 // eb0d | jmp 0xf // 6a01 | push 1 // ff15???????? | // e9???????? | $sequence_10 = { ff15???????? 8b4dfc c7410400000000 6830750000 ff15???????? } // n = 5, score = 100 // ff15???????? | // 8b4dfc | mov ecx, dword ptr [ebp - 4] // c7410400000000 | mov dword ptr [ecx + 4], 0 // 6830750000 | push 0x7530 // ff15???????? | $sequence_11 = { 8b8d64feffff 038d4cfeffff 8b9544feffff 8b048d30f62004 } // n = 4, score = 100 // 8b8d64feffff | mov ecx, dword ptr [ebp - 0x19c] // 038d4cfeffff | add ecx, dword ptr [ebp - 0x1b4] // 8b9544feffff | mov edx, dword ptr [ebp - 0x1bc] // 8b048d30f62004 | mov eax, dword ptr [ecx*4 + 0x420f630] $sequence_12 = { 7905 48 83c8fe 40 752a } // n = 5, score = 100 // 7905 | jns 7 // 48 | dec eax // 83c8fe | or eax, 0xfffffffe // 40 | inc eax // 752a | jne 0x2c $sequence_13 = { 83fa01 0f859d010000 8b856cfeffff 8b0c851cf62004 51 e8???????? } // n = 6, score = 100 // 83fa01 | cmp edx, 1 // 0f859d010000 | jne 0x1a3 // 8b856cfeffff | mov eax, dword ptr [ebp - 0x194] // 8b0c851cf62004 | mov ecx, dword ptr [eax*4 + 0x420f61c] // 51 | push ecx // e8???????? | $sequence_14 = { 8a8a7c310004 8808 ebc1 8b5508 03550c c60200 c745fc01000000 } // n = 7, score = 100 // 8a8a7c310004 | mov cl, byte ptr [edx + 0x400317c] // 8808 | mov byte ptr [eax], cl // ebc1 | jmp 0xffffffc3 // 8b5508 | mov edx, dword ptr [ebp + 8] // 03550c | add edx, dword ptr [ebp + 0xc] // c60200 | mov byte ptr [edx], 0 // c745fc01000000 | mov dword ptr [ebp - 4], 1 $sequence_15 = { 817df096000000 0f87a6000000 c745ec00000000 8d55ec } // n = 4, score = 100 // 817df096000000 | cmp dword ptr [ebp - 0x10], 0x96 // 0f87a6000000 | ja 0xac // c745ec00000000 | mov dword ptr [ebp - 0x14], 0 // 8d55ec | lea edx, [ebp - 0x14] condition: 7 of them and filesize < 262144 }
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