Actor(s): Anunak
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rule win_jssloader_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2022-04-08" version = "1" description = "Detects win.jssloader." 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.jssloader" malpedia_rule_date = "20220405" malpedia_hash = "ecd38294bd47d5589be5cd5490dc8bb4804afc2a" malpedia_version = "20220411" 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 = { 0f10856cfdffff c7401000000000 c6856cfdffff00 0f1100 c78594fdffff00000000 } // n = 5, score = 200 // 0f10856cfdffff | movups xmm0, xmmword ptr [ebp - 0x294] // c7401000000000 | mov dword ptr [eax + 0x10], 0 // c6856cfdffff00 | mov byte ptr [ebp - 0x294], 0 // 0f1100 | movups xmmword ptr [eax], xmm0 // c78594fdffff00000000 | mov dword ptr [ebp - 0x26c], 0 $sequence_1 = { 0f8768060000 e9???????? e8???????? 8bc8 c645fc07 8b7114 8bc6 } // n = 7, score = 200 // 0f8768060000 | ja 0x66e // e9???????? | // e8???????? | // 8bc8 | mov ecx, eax // c645fc07 | mov byte ptr [ebp - 4], 7 // 8b7114 | mov esi, dword ptr [ecx + 0x14] // 8bc6 | mov eax, esi $sequence_2 = { 660f289820a84300 660f2835???????? 660f59cf 660f58d1 } // n = 4, score = 200 // 660f289820a84300 | movapd xmm3, xmmword ptr [eax + 0x43a820] // 660f2835???????? | // 660f59cf | mulpd xmm1, xmm7 // 660f58d1 | addpd xmm2, xmm1 $sequence_3 = { 68???????? 6a00 c785f0feffff00000000 c785f4feffff0f000000 c685e0feffff00 ff15???????? 8d4b04 } // n = 7, score = 200 // 68???????? | // 6a00 | push 0 // c785f0feffff00000000 | mov dword ptr [ebp - 0x110], 0 // c785f4feffff0f000000 | mov dword ptr [ebp - 0x10c], 0xf // c685e0feffff00 | mov byte ptr [ebp - 0x120], 0 // ff15???????? | // 8d4b04 | lea ecx, dword ptr [ebx + 4] $sequence_4 = { 51 e8???????? 83c408 8b85bcfeffff c745ac00000000 c745b00f000000 c6459c00 } // n = 7, score = 200 // 51 | push ecx // e8???????? | // 83c408 | add esp, 8 // 8b85bcfeffff | mov eax, dword ptr [ebp - 0x144] // c745ac00000000 | mov dword ptr [ebp - 0x54], 0 // c745b00f000000 | mov dword ptr [ebp - 0x50], 0xf // c6459c00 | mov byte ptr [ebp - 0x64], 0 $sequence_5 = { 8d4dc0 e8???????? 8b5dd0 c645fc03 8d55c0 837dd410 8d8de8feffff } // n = 7, score = 200 // 8d4dc0 | lea ecx, dword ptr [ebp - 0x40] // e8???????? | // 8b5dd0 | mov ebx, dword ptr [ebp - 0x30] // c645fc03 | mov byte ptr [ebp - 4], 3 // 8d55c0 | lea edx, dword ptr [ebp - 0x40] // 837dd410 | cmp dword ptr [ebp - 0x2c], 0x10 // 8d8de8feffff | lea ecx, dword ptr [ebp - 0x118] $sequence_6 = { 83f81f 0f872b010000 52 51 e8???????? 83c408 837e1410 } // n = 7, score = 200 // 83f81f | cmp eax, 0x1f // 0f872b010000 | ja 0x131 // 52 | push edx // 51 | push ecx // e8???????? | // 83c408 | add esp, 8 // 837e1410 | cmp dword ptr [esi + 0x14], 0x10 $sequence_7 = { c1fa06 8bce 83e13f 6bc938 8b0495701d4400 c644082801 8b0495701d4400 } // n = 7, score = 200 // c1fa06 | sar edx, 6 // 8bce | mov ecx, esi // 83e13f | and ecx, 0x3f // 6bc938 | imul ecx, ecx, 0x38 // 8b0495701d4400 | mov eax, dword ptr [edx*4 + 0x441d70] // c644082801 | mov byte ptr [eax + ecx + 0x28], 1 // 8b0495701d4400 | mov eax, dword ptr [edx*4 + 0x441d70] $sequence_8 = { 03f0 56 e8???????? 8b8534ffffff 83c40c 8b8d54feffff } // n = 6, score = 200 // 03f0 | add esi, eax // 56 | push esi // e8???????? | // 8b8534ffffff | mov eax, dword ptr [ebp - 0xcc] // 83c40c | add esp, 0xc // 8b8d54feffff | mov ecx, dword ptr [ebp - 0x1ac] $sequence_9 = { 57 8b7d08 eb6f 8b07 8d1c85581a4400 8b33 85f6 } // n = 7, score = 200 // 57 | push edi // 8b7d08 | mov edi, dword ptr [ebp + 8] // eb6f | jmp 0x71 // 8b07 | mov eax, dword ptr [edi] // 8d1c85581a4400 | lea ebx, dword ptr [eax*4 + 0x441a58] // 8b33 | mov esi, dword ptr [ebx] // 85f6 | test esi, esi condition: 7 of them and filesize < 581632 }
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