Mandiant associates this with UNC4191, this malware decrypts and runs DARKDEW.
rule win_mistcloak_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-01-25" version = "1" description = "Detects win.mistcloak." 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.mistcloak" 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 = { 56 8b048590500110 8b7508 57 8bfe 8b440818 } // n = 6, score = 100 // 56 | push esi // 8b048590500110 | mov eax, dword ptr [eax*4 + 0x10015090] // 8b7508 | mov esi, dword ptr [ebp + 8] // 57 | push edi // 8bfe | mov edi, esi // 8b440818 | mov eax, dword ptr [eax + ecx + 0x18] $sequence_1 = { 8b4dd8 83c40c 8b55dc 8b7db4 8bf3 8b04bd90500110 } // n = 6, score = 100 // 8b4dd8 | mov ecx, dword ptr [ebp - 0x28] // 83c40c | add esp, 0xc // 8b55dc | mov edx, dword ptr [ebp - 0x24] // 8b7db4 | mov edi, dword ptr [ebp - 0x4c] // 8bf3 | mov esi, ebx // 8b04bd90500110 | mov eax, dword ptr [edi*4 + 0x10015090] $sequence_2 = { 8bc1 3914c5781a0110 7408 40 83f81d 7cf1 } // n = 6, score = 100 // 8bc1 | mov eax, ecx // 3914c5781a0110 | cmp dword ptr [eax*8 + 0x10011a78], edx // 7408 | je 0xa // 40 | inc eax // 83f81d | cmp eax, 0x1d // 7cf1 | jl 0xfffffff3 $sequence_3 = { 8d1c8500500110 8b03 90 8b15???????? 83cfff 8bca } // n = 6, score = 100 // 8d1c8500500110 | lea ebx, [eax*4 + 0x10015000] // 8b03 | mov eax, dword ptr [ebx] // 90 | nop // 8b15???????? | // 83cfff | or edi, 0xffffffff // 8bca | mov ecx, edx $sequence_4 = { 83e73f c1f906 6bd738 8b0c8d90500110 c644112800 } // n = 5, score = 100 // 83e73f | and edi, 0x3f // c1f906 | sar ecx, 6 // 6bd738 | imul edx, edi, 0x38 // 8b0c8d90500110 | mov ecx, dword ptr [ecx*4 + 0x10015090] // c644112800 | mov byte ptr [ecx + edx + 0x28], 0 $sequence_5 = { 57 6a00 ff15???????? 8bf0 8d45c8 } // n = 5, score = 100 // 57 | push edi // 6a00 | push 0 // ff15???????? | // 8bf0 | mov esi, eax // 8d45c8 | lea eax, [ebp - 0x38] $sequence_6 = { 47 84c0 75f8 b911000000 8d85c4feffff be???????? } // n = 6, score = 100 // 47 | inc edi // 84c0 | test al, al // 75f8 | jne 0xfffffffa // b911000000 | mov ecx, 0x11 // 8d85c4feffff | lea eax, [ebp - 0x13c] // be???????? | $sequence_7 = { 90 90 8d45c0 6a32 } // n = 4, score = 100 // 90 | nop // 90 | nop // 8d45c0 | lea eax, [ebp - 0x40] // 6a32 | push 0x32 $sequence_8 = { 83e63f c1f906 6bf638 8b0c8d90500110 } // n = 4, score = 100 // 83e63f | and esi, 0x3f // c1f906 | sar ecx, 6 // 6bf638 | imul esi, esi, 0x38 // 8b0c8d90500110 | mov ecx, dword ptr [ecx*4 + 0x10015090] $sequence_9 = { 58 8b55f8 33c9 837dfc32 8b75f4 } // n = 5, score = 100 // 58 | pop eax // 8b55f8 | mov edx, dword ptr [ebp - 8] // 33c9 | xor ecx, ecx // 837dfc32 | cmp dword ptr [ebp - 4], 0x32 // 8b75f4 | mov esi, dword ptr [ebp - 0xc] condition: 7 of them and filesize < 196608 }
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