According to Trend Micro, this is a loader for win.transbox, used by threat actor Earth Yako.
rule win_mirrorkey_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2026-05-04" version = "1" description = "Detects win.mirrorkey." 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.mirrorkey" malpedia_rule_date = "20260422" malpedia_hash = "a182e35da64e6d71cb55f125c4d4225196523f14" malpedia_version = "20260504" 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 = { 5d c20800 e9???????? 3b0d???????? f27502 f2c3 f2e9ca030000 } // n = 7, score = 100 // 5d | pop ebp // c20800 | ret 8 // e9???????? | // 3b0d???????? | // f27502 | bnd jne 5 // f2c3 | bnd ret // f2e9ca030000 | bnd jmp 0x3d0 $sequence_1 = { 57 8b13 0f57c0 8b7d0c 83c2e0 50 } // n = 6, score = 100 // 57 | push edi // 8b13 | mov edx, dword ptr [ebx] // 0f57c0 | xorps xmm0, xmm0 // 8b7d0c | mov edi, dword ptr [ebp + 0xc] // 83c2e0 | add edx, -0x20 // 50 | push eax $sequence_2 = { 8b06 eb02 8bc6 c60000 c745fc00000000 8bce a1???????? } // n = 7, score = 100 // 8b06 | mov eax, dword ptr [esi] // eb02 | jmp 4 // 8bc6 | mov eax, esi // c60000 | mov byte ptr [eax], 0 // c745fc00000000 | mov dword ptr [ebp - 4], 0 // 8bce | mov ecx, esi // a1???????? | $sequence_3 = { 68???????? ff15???????? 57 8b7d18 } // n = 4, score = 100 // 68???????? | // ff15???????? | // 57 | push edi // 8b7d18 | mov edi, dword ptr [ebp + 0x18] $sequence_4 = { 6aff 6a00 56 8d4db8 c745cc0f000000 c745c800000000 c645b800 } // n = 7, score = 100 // 6aff | push -1 // 6a00 | push 0 // 56 | push esi // 8d4db8 | lea ecx, [ebp - 0x48] // c745cc0f000000 | mov dword ptr [ebp - 0x34], 0xf // c745c800000000 | mov dword ptr [ebp - 0x38], 0 // c645b800 | mov byte ptr [ebp - 0x48], 0 $sequence_5 = { 50 e8???????? ff75fc 8d45fc ff75f8 50 } // n = 6, score = 100 // 50 | push eax // e8???????? | // ff75fc | push dword ptr [ebp - 4] // 8d45fc | lea eax, [ebp - 4] // ff75f8 | push dword ptr [ebp - 8] // 50 | push eax $sequence_6 = { 51 e8???????? ff7004 ff30 ff15???????? 83c41c } // n = 6, score = 100 // 51 | push ecx // e8???????? | // ff7004 | push dword ptr [eax + 4] // ff30 | push dword ptr [eax] // ff15???????? | // 83c41c | add esp, 0x1c $sequence_7 = { 56 ff15???????? 5f 5e c7430400000000 } // n = 5, score = 100 // 56 | push esi // ff15???????? | // 5f | pop edi // 5e | pop esi // c7430400000000 | mov dword ptr [ebx + 4], 0 $sequence_8 = { 46 3bf3 7ccf 8b4dfc } // n = 4, score = 100 // 46 | inc esi // 3bf3 | cmp esi, ebx // 7ccf | jl 0xffffffd1 // 8b4dfc | mov ecx, dword ptr [ebp - 4] $sequence_9 = { 85c0 7405 8a0c06 eb03 8a4ef4 } // n = 5, score = 100 // 85c0 | test eax, eax // 7405 | je 7 // 8a0c06 | mov cl, byte ptr [esi + eax] // eb03 | jmp 5 // 8a4ef4 | mov cl, byte ptr [esi - 0xc] condition: 7 of them and filesize < 117760 }
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