Actor(s): NARWHAL SPIDER
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rule win_cutwail_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2022-05-16" version = "1" description = "Detects win.cutwail." 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.cutwail" 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 = { 8b3c38 89540f04 8b556c 8b1410 } // n = 4, score = 100 // 8b3c38 | mov edi, dword ptr [eax + edi] // 89540f04 | mov dword ptr [edi + ecx + 4], edx // 8b556c | mov edx, dword ptr [ebp + 0x6c] // 8b1410 | mov edx, dword ptr [eax + edx] $sequence_1 = { 53 53 8d8554feffff 50 688e000000 } // n = 5, score = 100 // 53 | push ebx // 53 | push ebx // 8d8554feffff | lea eax, [ebp - 0x1ac] // 50 | push eax // 688e000000 | push 0x8e $sequence_2 = { c78564feffff00000000 ff15???????? 898568feffff c68563feffff00 83bd6cfeffff00 } // n = 5, score = 100 // c78564feffff00000000 | mov dword ptr [ebp - 0x19c], 0 // ff15???????? | // 898568feffff | mov dword ptr [ebp - 0x198], eax // c68563feffff00 | mov byte ptr [ebp - 0x19d], 0 // 83bd6cfeffff00 | cmp dword ptr [ebp - 0x194], 0 $sequence_3 = { 50 897d48 897d14 c6455b00 } // n = 4, score = 100 // 50 | push eax // 897d48 | mov dword ptr [ebp + 0x48], edi // 897d14 | mov dword ptr [ebp + 0x14], edi // c6455b00 | mov byte ptr [ebp + 0x5b], 0 $sequence_4 = { ff15???????? e9???????? 8b956cfeffff 83c201 89956cfeffff } // n = 5, score = 100 // ff15???????? | // e9???????? | // 8b956cfeffff | mov edx, dword ptr [ebp - 0x194] // 83c201 | add edx, 1 // 89956cfeffff | mov dword ptr [ebp - 0x194], edx $sequence_5 = { 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_6 = { 894d10 ebc3 6a00 6a00 8b550c 52 } // n = 6, score = 100 // 894d10 | mov dword ptr [ebp + 0x10], ecx // ebc3 | jmp 0xffffffc5 // 6a00 | push 0 // 6a00 | push 0 // 8b550c | mov edx, dword ptr [ebp + 0xc] // 52 | push edx $sequence_7 = { e8???????? 8b0f 83c410 395d0c } // n = 4, score = 100 // e8???????? | // 8b0f | mov ecx, dword ptr [edi] // 83c410 | add esp, 0x10 // 395d0c | cmp dword ptr [ebp + 0xc], ebx $sequence_8 = { 7419 8b4518 833800 7511 837df800 7e0b } // n = 6, score = 100 // 7419 | je 0x1b // 8b4518 | mov eax, dword ptr [ebp + 0x18] // 833800 | cmp dword ptr [eax], 0 // 7511 | jne 0x13 // 837df800 | cmp dword ptr [ebp - 8], 0 // 7e0b | jle 0xd $sequence_9 = { 8b8d5cfeffff 3b8d68feffff 730e 8b955cfeffff 899568feffff eb46 } // n = 6, score = 100 // 8b8d5cfeffff | mov ecx, dword ptr [ebp - 0x1a4] // 3b8d68feffff | cmp ecx, dword ptr [ebp - 0x198] // 730e | jae 0x10 // 8b955cfeffff | mov edx, dword ptr [ebp - 0x1a4] // 899568feffff | mov dword ptr [ebp - 0x198], edx // eb46 | jmp 0x48 $sequence_10 = { 83c404 8985e4fdffff 6a07 e8???????? 83c404 8985e8fdffff 6888130000 } // n = 7, score = 100 // 83c404 | add esp, 4 // 8985e4fdffff | mov dword ptr [ebp - 0x21c], eax // 6a07 | push 7 // e8???????? | // 83c404 | add esp, 4 // 8985e8fdffff | mov dword ptr [ebp - 0x218], eax // 6888130000 | push 0x1388 $sequence_11 = { eb77 83bd6cfeffff05 7d6e ff15???????? 89855cfeffff 8b8d5cfeffff 3b8d68feffff } // n = 7, score = 100 // eb77 | jmp 0x79 // 83bd6cfeffff05 | cmp dword ptr [ebp - 0x194], 5 // 7d6e | jge 0x70 // ff15???????? | // 89855cfeffff | mov dword ptr [ebp - 0x1a4], eax // 8b8d5cfeffff | mov ecx, dword ptr [ebp - 0x1a4] // 3b8d68feffff | cmp ecx, dword ptr [ebp - 0x198] $sequence_12 = { 51 e8???????? 8b4550 8b4d74 } // n = 4, score = 100 // 51 | push ecx // e8???????? | // 8b4550 | mov eax, dword ptr [ebp + 0x50] // 8b4d74 | mov ecx, dword ptr [ebp + 0x74] $sequence_13 = { 8bf8 83c410 3bfb 7422 } // n = 4, score = 100 // 8bf8 | mov edi, eax // 83c410 | add esp, 0x10 // 3bfb | cmp edi, ebx // 7422 | je 0x24 $sequence_14 = { 33c0 ebf7 8b442404 8b4808 } // n = 4, score = 100 // 33c0 | xor eax, eax // ebf7 | jmp 0xfffffff9 // 8b442404 | mov eax, dword ptr [esp + 4] // 8b4808 | mov ecx, dword ptr [eax + 8] $sequence_15 = { 7459 8b06 3bc7 7453 } // n = 4, score = 100 // 7459 | je 0x5b // 8b06 | mov eax, dword ptr [esi] // 3bc7 | cmp eax, edi // 7453 | je 0x55 condition: 7 of them and filesize < 262144 }
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