Downloader used in suspected APT attack against Vietnam.
rule win_5t_downloader_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-12-06" version = "1" description = "Detects win.5t_downloader." 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.5t_downloader" 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 = { 7409 83781800 7403 5d } // n = 4, score = 500 // 7409 | je 0xb // 83781800 | cmp dword ptr [eax + 0x18], 0 // 7403 | je 5 // 5d | pop ebp $sequence_1 = { 85c9 7409 83781800 7403 5d } // n = 5, score = 500 // 85c9 | test ecx, ecx // 7409 | je 0xb // 83781800 | cmp dword ptr [eax + 0x18], 0 // 7403 | je 5 // 5d | pop ebp $sequence_2 = { 85c9 7409 83781800 7403 } // n = 4, score = 500 // 85c9 | test ecx, ecx // 7409 | je 0xb // 83781800 | cmp dword ptr [eax + 0x18], 0 // 7403 | je 5 $sequence_3 = { 85c0 7416 83781400 7510 } // n = 4, score = 500 // 85c0 | test eax, eax // 7416 | je 0x18 // 83781400 | cmp dword ptr [eax + 0x14], 0 // 7510 | jne 0x12 $sequence_4 = { 85c9 7409 83781800 7403 5d ffe1 83c8ff } // n = 7, score = 500 // 85c9 | test ecx, ecx // 7409 | je 0xb // 83781800 | cmp dword ptr [eax + 0x18], 0 // 7403 | je 5 // 5d | pop ebp // ffe1 | jmp ecx // 83c8ff | or eax, 0xffffffff $sequence_5 = { 8b4508 85c0 7416 83781400 7510 } // n = 5, score = 500 // 8b4508 | mov eax, dword ptr [ebp + 8] // 85c0 | test eax, eax // 7416 | je 0x18 // 83781400 | cmp dword ptr [eax + 0x14], 0 // 7510 | jne 0x12 $sequence_6 = { 55 8bec 8b4508 85c0 7416 83781400 7510 } // n = 7, score = 500 // 55 | push ebp // 8bec | mov ebp, esp // 8b4508 | mov eax, dword ptr [ebp + 8] // 85c0 | test eax, eax // 7416 | je 0x18 // 83781400 | cmp dword ptr [eax + 0x14], 0 // 7510 | jne 0x12 $sequence_7 = { 85c9 7409 83781800 7403 5d ffe1 } // n = 6, score = 500 // 85c9 | test ecx, ecx // 7409 | je 0xb // 83781800 | cmp dword ptr [eax + 0x18], 0 // 7403 | je 5 // 5d | pop ebp // ffe1 | jmp ecx $sequence_8 = { 7409 83781800 7403 5d ffe1 83c8ff } // n = 6, score = 500 // 7409 | je 0xb // 83781800 | cmp dword ptr [eax + 0x18], 0 // 7403 | je 5 // 5d | pop ebp // ffe1 | jmp ecx // 83c8ff | or eax, 0xffffffff $sequence_9 = { 8bec 8b4508 85c0 7416 83781400 7510 } // n = 6, score = 500 // 8bec | mov ebp, esp // 8b4508 | mov eax, dword ptr [ebp + 8] // 85c0 | test eax, eax // 7416 | je 0x18 // 83781400 | cmp dword ptr [eax + 0x14], 0 // 7510 | jne 0x12 condition: 7 of them and filesize < 539648 }
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