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rule win_cmstar_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-01-25" 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 = "20230124" malpedia_hash = "2ee0eebba83dce3d019a90519f2f972c0fcf9686" malpedia_version = "20230125" 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 = { ff15???????? 6a04 e8???????? be00040000 } // n = 4, score = 800 // ff15???????? | // 6a04 | push 4 // e8???????? | // be00040000 | mov esi, 0x400 $sequence_1 = { 56 bb04010000 57 53 } // n = 4, score = 800 // 56 | push esi // bb04010000 | mov ebx, 0x104 // 57 | push edi // 53 | push ebx $sequence_2 = { 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_3 = { 8b4dec c1e802 6a04 52 8d0481 50 } // n = 6, 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 $sequence_4 = { ff15???????? 8bc6 e9???????? 6a10 8d45d0 53 } // n = 6, score = 800 // ff15???????? | // 8bc6 | mov eax, esi // e9???????? | // 6a10 | push 0x10 // 8d45d0 | lea eax, [ebp - 0x30] // 53 | push ebx $sequence_5 = { ff75fc 8945e0 8b45dc 83c310 } // n = 4, score = 800 // ff75fc | push dword ptr [ebp - 4] // 8945e0 | mov dword ptr [ebp - 0x20], eax // 8b45dc | mov eax, dword ptr [ebp - 0x24] // 83c310 | add ebx, 0x10 $sequence_6 = { 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_7 = { 8b45d8 836dfc10 ff75fc 8945e0 } // n = 4, 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 $sequence_8 = { 885c247c f3ab 66ab aa b908020000 } // n = 5, score = 100 // 885c247c | mov byte ptr [esp + 0x7c], bl // f3ab | rep stosd dword ptr es:[edi], eax // 66ab | stosw word ptr es:[edi], ax // aa | stosb byte ptr es:[edi], al // b908020000 | mov ecx, 0x208 $sequence_9 = { ff15???????? 8b54242c 89442418 52 50 e8???????? } // n = 6, score = 100 // ff15???????? | // 8b54242c | mov edx, dword ptr [esp + 0x2c] // 89442418 | mov dword ptr [esp + 0x18], eax // 52 | push edx // 50 | push eax // e8???????? | $sequence_10 = { 8b54241c 881c2f 47 3bfa } // n = 4, score = 100 // 8b54241c | mov edx, dword ptr [esp + 0x1c] // 881c2f | mov byte ptr [edi + ebp], bl // 47 | inc edi // 3bfa | cmp edi, edx $sequence_11 = { 83c9ff f2ae f7d1 49 8d7c0c18 8bcd 8bc1 } // n = 7, score = 100 // 83c9ff | or ecx, 0xffffffff // f2ae | repne scasb al, byte ptr es:[edi] // f7d1 | not ecx // 49 | dec ecx // 8d7c0c18 | lea edi, [esp + ecx + 0x18] // 8bcd | mov ecx, ebp // 8bc1 | mov eax, ecx $sequence_12 = { 8b6c2414 56 57 8b7c2418 8bcb 8bf7 8bd5 } // n = 7, score = 100 // 8b6c2414 | mov ebp, dword ptr [esp + 0x14] // 56 | push esi // 57 | push edi // 8b7c2418 | mov edi, dword ptr [esp + 0x18] // 8bcb | mov ecx, ebx // 8bf7 | mov esi, edi // 8bd5 | mov edx, ebp $sequence_13 = { bf???????? be???????? 66895c0c18 83c9ff f2ae } // n = 5, score = 100 // bf???????? | // be???????? | // 66895c0c18 | mov word ptr [esp + ecx + 0x18], bx // 83c9ff | or ecx, 0xffffffff // f2ae | repne scasb al, byte ptr es:[edi] $sequence_14 = { 741e 8a441420 bf???????? 8882a8430010 83c9ff } // n = 5, score = 100 // 741e | je 0x20 // 8a441420 | mov al, byte ptr [esp + edx + 0x20] // bf???????? | // 8882a8430010 | mov byte ptr [edx + 0x100043a8], al // 83c9ff | or ecx, 0xffffffff $sequence_15 = { 53 8bd1 8bf7 83c9ff bf???????? f2ae } // n = 6, score = 100 // 53 | push ebx // 8bd1 | mov edx, ecx // 8bf7 | mov esi, edi // 83c9ff | or ecx, 0xffffffff // bf???????? | // f2ae | repne scasb al, byte ptr es:[edi] 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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