A downloader trojan with some infostealer capabilities focused on the browser. Previously observed as part of RigEK campaigns.
rule win_snatch_loader_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-01-25" version = "1" description = "Detects win.snatch_loader." 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.snatch_loader" 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 = { 85f6 744b 33c0 66894606 a1???????? 85c0 } // n = 6, score = 600 // 85f6 | test esi, esi // 744b | je 0x4d // 33c0 | xor eax, eax // 66894606 | mov word ptr [esi + 6], ax // a1???????? | // 85c0 | test eax, eax $sequence_1 = { e8???????? a3???????? 85c0 7505 8b45fc eb05 } // n = 6, score = 600 // e8???????? | // a3???????? | // 85c0 | test eax, eax // 7505 | jne 7 // 8b45fc | mov eax, dword ptr [ebp - 4] // eb05 | jmp 7 $sequence_2 = { 53 53 8d4dfc 51 53 53 56 } // n = 7, score = 600 // 53 | push ebx // 53 | push ebx // 8d4dfc | lea ecx, [ebp - 4] // 51 | push ecx // 53 | push ebx // 53 | push ebx // 56 | push esi $sequence_3 = { 33d2 85c9 5e 0f45c2 8be5 } // n = 5, score = 600 // 33d2 | xor edx, edx // 85c9 | test ecx, ecx // 5e | pop esi // 0f45c2 | cmovne eax, edx // 8be5 | mov esp, ebp $sequence_4 = { 8bd8 a1???????? 85c0 751d 33c9 } // n = 5, score = 600 // 8bd8 | mov ebx, eax // a1???????? | // 85c0 | test eax, eax // 751d | jne 0x1f // 33c9 | xor ecx, ecx $sequence_5 = { 33db bfe71edec0 895dfc e8???????? 8bf0 } // n = 5, score = 600 // 33db | xor ebx, ebx // bfe71edec0 | mov edi, 0xc0de1ee7 // 895dfc | mov dword ptr [ebp - 4], ebx // e8???????? | // 8bf0 | mov esi, eax $sequence_6 = { 8b7dfc eb04 ffd0 8bf8 a1???????? 85c0 } // n = 6, score = 600 // 8b7dfc | mov edi, dword ptr [ebp - 4] // eb04 | jmp 6 // ffd0 | call eax // 8bf8 | mov edi, eax // a1???????? | // 85c0 | test eax, eax $sequence_7 = { 83c002 668945f6 a1???????? 85c0 7522 33c9 } // n = 6, score = 600 // 83c002 | add eax, 2 // 668945f6 | mov word ptr [ebp - 0xa], ax // a1???????? | // 85c0 | test eax, eax // 7522 | jne 0x24 // 33c9 | xor ecx, ecx $sequence_8 = { 57 51 52 ff750c e8???????? } // n = 5, score = 500 // 57 | push edi // 51 | push ecx // 52 | push edx // ff750c | push dword ptr [ebp + 0xc] // e8???????? | $sequence_9 = { 59 5b 5a c9 c20c00 55 8bec } // n = 7, score = 500 // 59 | pop ecx // 5b | pop ebx // 5a | pop edx // c9 | leave // c20c00 | ret 0xc // 55 | push ebp // 8bec | mov ebp, esp $sequence_10 = { 03c6 ab 5b 5e eb03 } // n = 5, score = 500 // 03c6 | add eax, esi // ab | stosd dword ptr es:[edi], eax // 5b | pop ebx // 5e | pop esi // eb03 | jmp 5 $sequence_11 = { 76d8 33c0 48 5a 59 5f } // n = 6, score = 500 // 76d8 | jbe 0xffffffda // 33c0 | xor eax, eax // 48 | dec eax // 5a | pop edx // 59 | pop ecx // 5f | pop edi $sequence_12 = { 57 56 8b36 56 8b33 33c0 } // n = 6, score = 500 // 57 | push edi // 56 | push esi // 8b36 | mov esi, dword ptr [esi] // 56 | push esi // 8b33 | mov esi, dword ptr [ebx] // 33c0 | xor eax, eax $sequence_13 = { 0bc0 7440 3b45fc 773b 8b750c 8b7d10 037508 } // n = 7, score = 500 // 0bc0 | or eax, eax // 7440 | je 0x42 // 3b45fc | cmp eax, dword ptr [ebp - 4] // 773b | ja 0x3d // 8b750c | mov esi, dword ptr [ebp + 0xc] // 8b7d10 | mov edi, dword ptr [ebp + 0x10] // 037508 | add esi, dword ptr [ebp + 8] $sequence_14 = { 7454 394508 734f ff7510 } // n = 4, score = 500 // 7454 | je 0x56 // 394508 | cmp dword ptr [ebp + 8], eax // 734f | jae 0x51 // ff7510 | push dword ptr [ebp + 0x10] $sequence_15 = { 33d2 33c9 8a0431 0ac0 } // n = 4, score = 500 // 33d2 | xor edx, edx // 33c9 | xor ecx, ecx // 8a0431 | mov al, byte ptr [ecx + esi] // 0ac0 | or al, al condition: 7 of them and filesize < 262144 }
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