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rule win_cmstar_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-07-11" version = "1" description = "Detects win.cmstar." 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.cmstar" 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 = { 56 bb04010000 57 53 } // n = 4, score = 800 // 56 | push esi // bb04010000 | mov ebx, 0x104 // 57 | push edi // 53 | push ebx $sequence_1 = { ff15???????? 8bc6 e9???????? 6a10 8d45d0 } // n = 5, score = 800 // ff15???????? | // 8bc6 | mov eax, esi // e9???????? | // 6a10 | push 0x10 // 8d45d0 | lea eax, [ebp - 0x30] $sequence_2 = { 85c0 7504 6a03 eb0d 803b4d } // n = 5, score = 800 // 85c0 | test eax, eax // 7504 | jne 6 // 6a03 | push 3 // eb0d | jmp 0xf // 803b4d | cmp byte ptr [ebx], 0x4d $sequence_3 = { 8b45d8 836dfc10 ff75fc 8945e0 8b45dc } // n = 5, score = 800 // 8b45d8 | mov eax, dword ptr [ebp - 0x28] // 836dfc10 | sub dword ptr [ebp - 4], 0x10 // ff75fc | push dword ptr [ebp - 4] // 8945e0 | mov dword ptr [ebp - 0x20], eax // 8b45dc | mov eax, dword ptr [ebp - 0x24] $sequence_4 = { 8b4dec c1e802 6a04 52 8d0481 50 e8???????? } // n = 7, score = 800 // 8b4dec | mov ecx, dword ptr [ebp - 0x14] // c1e802 | shr eax, 2 // 6a04 | push 4 // 52 | push edx // 8d0481 | lea eax, [ecx + eax*4] // 50 | push eax // e8???????? | $sequence_5 = { ff15???????? 6a04 e8???????? be00040000 } // n = 4, score = 800 // ff15???????? | // 6a04 | push 4 // e8???????? | // be00040000 | mov esi, 0x400 $sequence_6 = { ff15???????? 6a03 58 5f 5e 5b c9 } // n = 7, score = 800 // ff15???????? | // 6a03 | push 3 // 58 | pop eax // 5f | pop edi // 5e | pop esi // 5b | pop ebx // c9 | leave $sequence_7 = { ff75e0 ff30 e8???????? 8b4df8 } // n = 4, score = 800 // ff75e0 | push dword ptr [ebp - 0x20] // ff30 | push dword ptr [eax] // e8???????? | // 8b4df8 | mov ecx, dword ptr [ebp - 8] $sequence_8 = { 50 8b44242c 55 50 ff15???????? 8bf0 } // n = 6, score = 100 // 50 | push eax // 8b44242c | mov eax, dword ptr [esp + 0x2c] // 55 | push ebp // 50 | push eax // ff15???????? | // 8bf0 | mov esi, eax $sequence_9 = { 5d 0bc0 5b 81c408060000 c3 } // n = 5, score = 100 // 5d | pop ebp // 0bc0 | or eax, eax // 5b | pop ebx // 81c408060000 | add esp, 0x608 // c3 | ret $sequence_10 = { ff15???????? 3db7000000 7505 33c0 c20c00 6a00 } // n = 6, score = 100 // ff15???????? | // 3db7000000 | cmp eax, 0xb7 // 7505 | jne 7 // 33c0 | xor eax, eax // c20c00 | ret 0xc // 6a00 | push 0 $sequence_11 = { bf???????? be???????? 88540c18 83c9ff } // n = 4, score = 100 // bf???????? | // be???????? | // 88540c18 | mov byte ptr [esp + ecx + 0x18], dl // 83c9ff | or ecx, 0xffffffff $sequence_12 = { 53 ff15???????? 68???????? 57 ff15???????? 8bf0 83c408 } // n = 7, score = 100 // 53 | push ebx // ff15???????? | // 68???????? | // 57 | push edi // ff15???????? | // 8bf0 | mov esi, eax // 83c408 | add esp, 8 $sequence_13 = { 52 e8???????? 83c40c 8b0d???????? c68424cc12000002 8b11 b9???????? } // n = 7, score = 100 // 52 | push edx // e8???????? | // 83c40c | add esp, 0xc // 8b0d???????? | // c68424cc12000002 | mov byte ptr [esp + 0x12cc], 2 // 8b11 | mov edx, dword ptr [ecx] // b9???????? | $sequence_14 = { 741e 8a441420 bf???????? 888278420010 83c9ff 33c0 } // n = 6, score = 100 // 741e | je 0x20 // 8a441420 | mov al, byte ptr [esp + edx + 0x20] // bf???????? | // 888278420010 | mov byte ptr [edx + 0x10004278], al // 83c9ff | or ecx, 0xffffffff // 33c0 | xor eax, eax $sequence_15 = { 8bc8 53 83e103 6800000080 f3a4 53 68???????? } // n = 7, score = 100 // 8bc8 | mov ecx, eax // 53 | push ebx // 83e103 | and ecx, 3 // 6800000080 | push 0x80000000 // f3a4 | rep movsb byte ptr es:[edi], byte ptr [esi] // 53 | push ebx // 68???????? | condition: 7 of them and filesize < 4268032 }
import "pe" rule win_cmstar_w0 { meta: description = "Detects CMStar Malware" author = "Florian Roth" reference = "https://goo.gl/pTffPA" date = "2017-10-03" hash = "16697c95db5add6c1c23b2591b9d8eec5ed96074d057b9411f0b57a54af298d5" malpedia_reference = "https://malpedia.caad.fkie.fraunhofer.de/details/win.cmstar" malpedia_version = "20170413" malpedia_license = "CC BY-NC-SA 4.0" malpedia_sharing = "TLP:WHITE" strings: $s1 = "UpdateService.tmp" fullword ascii $s2 = "StateNum:%d,FileSize:%d" fullword ascii condition: uint16(0) == 0x5a4d and filesize < 100KB and (pe.imphash() == "22021985de78a48ea8fb82a2ff9eb693" or pe.exports("WinCred") or all of them) }
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