Actor(s): Anunak
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rule win_jssloader_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-12-06" 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 = "20231130" malpedia_hash = "fc8a0e9f343f6d6ded9e7df1a64dac0cc68d7351" malpedia_version = "20230808" 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 = { 89b5e0fbffff 660fd685e4fbffff 89b5ecfbffff 89b5e4fbffff 89b5e8fbffff 89b5ecfbffff } // n = 6, score = 200 // 89b5e0fbffff | mov dword ptr [ebp - 0x420], esi // 660fd685e4fbffff | movq qword ptr [ebp - 0x41c], xmm0 // 89b5ecfbffff | mov dword ptr [ebp - 0x414], esi // 89b5e4fbffff | mov dword ptr [ebp - 0x41c], esi // 89b5e8fbffff | mov dword ptr [ebp - 0x418], esi // 89b5ecfbffff | mov dword ptr [ebp - 0x414], esi $sequence_1 = { 0f4345b4 50 ff15???????? 8bf0 89b5c0fdffff 83feff 0f84b9020000 } // n = 7, score = 200 // 0f4345b4 | cmovae eax, dword ptr [ebp - 0x4c] // 50 | push eax // ff15???????? | // 8bf0 | mov esi, eax // 89b5c0fdffff | mov dword ptr [ebp - 0x240], esi // 83feff | cmp esi, -1 // 0f84b9020000 | je 0x2bf $sequence_2 = { 8945fc 56 8b7508 8d85fcfeffff 6800010000 6a00 50 } // n = 7, score = 200 // 8945fc | mov dword ptr [ebp - 4], eax // 56 | push esi // 8b7508 | mov esi, dword ptr [ebp + 8] // 8d85fcfeffff | lea eax, [ebp - 0x104] // 6800010000 | push 0x100 // 6a00 | push 0 // 50 | push eax $sequence_3 = { 899d0cffffff 6a04 68???????? c745d000000000 c745d40f000000 c645c000 e8???????? } // n = 7, score = 200 // 899d0cffffff | mov dword ptr [ebp - 0xf4], ebx // 6a04 | push 4 // 68???????? | // c745d000000000 | mov dword ptr [ebp - 0x30], 0 // c745d40f000000 | mov dword ptr [ebp - 0x2c], 0xf // c645c000 | mov byte ptr [ebp - 0x40], 0 // e8???????? | $sequence_4 = { 2bc6 83c0fc 83f81f 0f8797010000 e9???????? 8b854cfeffff 8d4804 } // n = 7, score = 200 // 2bc6 | sub eax, esi // 83c0fc | add eax, -4 // 83f81f | cmp eax, 0x1f // 0f8797010000 | ja 0x19d // e9???????? | // 8b854cfeffff | mov eax, dword ptr [ebp - 0x1b4] // 8d4804 | lea ecx, [eax + 4] $sequence_5 = { 51 ffb570feffff 8d4dcc e8???????? c645fc0b 8b55e0 8bc2 } // n = 7, score = 200 // 51 | push ecx // ffb570feffff | push dword ptr [ebp - 0x190] // 8d4dcc | lea ecx, [ebp - 0x34] // e8???????? | // c645fc0b | mov byte ptr [ebp - 4], 0xb // 8b55e0 | mov edx, dword ptr [ebp - 0x20] // 8bc2 | mov eax, edx $sequence_6 = { 3b85ecfbffff 740a 8808 ff85e8fbffff } // n = 4, score = 200 // 3b85ecfbffff | cmp eax, dword ptr [ebp - 0x414] // 740a | je 0xc // 8808 | mov byte ptr [eax], cl // ff85e8fbffff | inc dword ptr [ebp - 0x418] $sequence_7 = { 8bc1 83e13f c1f806 6bc938 8b0485701d4400 80640828fe ff33 } // n = 7, score = 200 // 8bc1 | mov eax, ecx // 83e13f | and ecx, 0x3f // c1f806 | sar eax, 6 // 6bc938 | imul ecx, ecx, 0x38 // 8b0485701d4400 | mov eax, dword ptr [eax*4 + 0x441d70] // 80640828fe | and byte ptr [eax + ecx + 0x28], 0xfe // ff33 | push dword ptr [ebx] $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 = { 03f0 56 e8???????? 8b854cffffff 83c40c c6043000 8bb568feffff } // n = 7, score = 200 // 03f0 | add esi, eax // 56 | push esi // e8???????? | // 8b854cffffff | mov eax, dword ptr [ebp - 0xb4] // 83c40c | add esp, 0xc // c6043000 | mov byte ptr [eax + esi], 0 // 8bb568feffff | mov esi, dword ptr [ebp - 0x198] condition: 7 of them and filesize < 581632 }
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