Downloader used in suspected APT attack against Vietnam.
rule win_5t_downloader_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-07-11" 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 = "20230705" malpedia_hash = "42d0574f4405bd7d2b154d321d345acb18834a41" malpedia_version = "20230715" 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 = { 889dd4feffff 899d84feffff 898588feffff 889d74feffff 33c0 } // n = 5, score = 300 // 889dd4feffff | mov byte ptr [ebp - 0x12c], bl // 899d84feffff | mov dword ptr [ebp - 0x17c], ebx // 898588feffff | mov dword ptr [ebp - 0x178], eax // 889d74feffff | mov byte ptr [ebp - 0x18c], bl // 33c0 | xor eax, eax $sequence_1 = { 8b4508 e8???????? c20c00 e8???????? cc 6a30 } // n = 6, score = 300 // 8b4508 | mov eax, dword ptr [ebp + 8] // e8???????? | // c20c00 | ret 0xc // e8???????? | // cc | int3 // 6a30 | push 0x30 $sequence_2 = { f2e9e3000000 55 8bec eb0d ff7508 e8???????? } // n = 6, score = 300 // f2e9e3000000 | bnd jmp 0xe9 // 55 | push ebp // 8bec | mov ebp, esp // eb0d | jmp 0xf // ff7508 | push dword ptr [ebp + 8] // e8???????? | $sequence_3 = { 83f904 0f8582000000 8b75d0 8bfb } // n = 4, score = 300 // 83f904 | cmp ecx, 4 // 0f8582000000 | jne 0x88 // 8b75d0 | mov esi, dword ptr [ebp - 0x30] // 8bfb | mov edi, ebx $sequence_4 = { eb0f ff7634 57 ff562c } // n = 4, score = 300 // eb0f | jmp 0x11 // ff7634 | push dword ptr [esi + 0x34] // 57 | push edi // ff562c | call dword ptr [esi + 0x2c] $sequence_5 = { 88041e 880c1f 0fb6041e 8b4dfc 03c2 8b550c } // n = 6, score = 300 // 88041e | mov byte ptr [esi + ebx], al // 880c1f | mov byte ptr [edi + ebx], cl // 0fb6041e | movzx eax, byte ptr [esi + ebx] // 8b4dfc | mov ecx, dword ptr [ebp - 4] // 03c2 | add eax, edx // 8b550c | mov edx, dword ptr [ebp + 0xc] $sequence_6 = { 3dffffff7f 0f87a2000000 03c0 3d00100000 7227 } // n = 5, score = 300 // 3dffffff7f | cmp eax, 0x7fffffff // 0f87a2000000 | ja 0xa8 // 03c0 | add eax, eax // 3d00100000 | cmp eax, 0x1000 // 7227 | jb 0x29 $sequence_7 = { 56 6a01 8d4dec 8975d8 } // n = 4, score = 300 // 56 | push esi // 6a01 | push 1 // 8d4dec | lea ecx, [ebp - 0x14] // 8975d8 | mov dword ptr [ebp - 0x28], esi condition: 7 of them and filesize < 389120 }
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