Actor(s): Anunak
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rule win_jssloader_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-01-25" 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 = "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 = { c78564ffffff00000000 c68568ffffff00 e8???????? 8d859cfeffff } // n = 4, score = 200 // c78564ffffff00000000 | mov dword ptr [ebp - 0x9c], 0 // c68568ffffff00 | mov byte ptr [ebp - 0x98], 0 // e8???????? | // 8d859cfeffff | lea eax, [ebp - 0x164] $sequence_1 = { 50 8b45e0 8b08 e8???????? 84c0 c645fc00 8b55cc } // n = 7, score = 200 // 50 | push eax // 8b45e0 | mov eax, dword ptr [ebp - 0x20] // 8b08 | mov ecx, dword ptr [eax] // e8???????? | // 84c0 | test al, al // c645fc00 | mov byte ptr [ebp - 4], 0 // 8b55cc | mov edx, dword ptr [ebp - 0x34] $sequence_2 = { 8b7dc0 8b45b0 0f43d7 8b75ac 2bc6 } // n = 5, score = 200 // 8b7dc0 | mov edi, dword ptr [ebp - 0x40] // 8b45b0 | mov eax, dword ptr [ebp - 0x50] // 0f43d7 | cmovae edx, edi // 8b75ac | mov esi, dword ptr [ebp - 0x54] // 2bc6 | sub eax, esi $sequence_3 = { 8bcf 83e73f c1f906 6bd738 8b0c8d701d4400 } // n = 5, score = 200 // 8bcf | mov ecx, edi // 83e73f | and edi, 0x3f // c1f906 | sar ecx, 6 // 6bd738 | imul edx, edi, 0x38 // 8b0c8d701d4400 | mov ecx, dword ptr [ecx*4 + 0x441d70] $sequence_4 = { 8b85f8feffff c745d000000000 c745d40f000000 c645c000 8b4004 c78405f8feffffa8be4300 8b85f8feffff } // n = 7, score = 200 // 8b85f8feffff | mov eax, dword ptr [ebp - 0x108] // c745d000000000 | mov dword ptr [ebp - 0x30], 0 // c745d40f000000 | mov dword ptr [ebp - 0x2c], 0xf // c645c000 | mov byte ptr [ebp - 0x40], 0 // 8b4004 | mov eax, dword ptr [eax + 4] // c78405f8feffffa8be4300 | mov dword ptr [ebp + eax - 0x108], 0x43bea8 // 8b85f8feffff | mov eax, dword ptr [ebp - 0x108] $sequence_5 = { 50 8d4dd4 e8???????? 8985b8feffff beffffff7f c645fc0e 8b55cc } // n = 7, score = 200 // 50 | push eax // 8d4dd4 | lea ecx, [ebp - 0x2c] // e8???????? | // 8985b8feffff | mov dword ptr [ebp - 0x148], eax // beffffff7f | mov esi, 0x7fffffff // c645fc0e | mov byte ptr [ebp - 4], 0xe // 8b55cc | mov edx, dword ptr [ebp - 0x34] $sequence_6 = { 7408 40 83f81d 7cf1 eb07 8b0cc57c3f4300 894de4 } // n = 7, score = 200 // 7408 | je 0xa // 40 | inc eax // 83f81d | cmp eax, 0x1d // 7cf1 | jl 0xfffffff3 // eb07 | jmp 9 // 8b0cc57c3f4300 | mov ecx, dword ptr [eax*8 + 0x433f7c] // 894de4 | mov dword ptr [ebp - 0x1c], ecx $sequence_7 = { 83f810 7231 8b953cffffff 8d4801 8bc2 } // n = 5, score = 200 // 83f810 | cmp eax, 0x10 // 7231 | jb 0x33 // 8b953cffffff | mov edx, dword ptr [ebp - 0xc4] // 8d4801 | lea ecx, [eax + 1] // 8bc2 | mov eax, edx $sequence_8 = { e8???????? 8be5 5d c20c00 8b854cfeffff 8d4804 } // n = 6, score = 200 // e8???????? | // 8be5 | mov esp, ebp // 5d | pop ebp // c20c00 | ret 0xc // 8b854cfeffff | mov eax, dword ptr [ebp - 0x1b4] // 8d4804 | lea ecx, [eax + 4] $sequence_9 = { b8abaaaa2a 2bcf 895df0 f7e9 8b4b04 c1fa03 2bcf } // n = 7, score = 200 // b8abaaaa2a | mov eax, 0x2aaaaaab // 2bcf | sub ecx, edi // 895df0 | mov dword ptr [ebp - 0x10], ebx // f7e9 | imul ecx // 8b4b04 | mov ecx, dword ptr [ebx + 4] // c1fa03 | sar edx, 3 // 2bcf | sub ecx, edi condition: 7 of them and filesize < 581632 }
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