Malware written in Nim, stealing data including discord tokens from browsers, exfiltrating the results via a Discord webhook.
rule win_nimgrabber_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-07-11" version = "1" description = "Detects win.nimgrabber." 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.nimgrabber" 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 = { 8b9424b4000000 0301 895008 8b9424b8000000 89500c 8b9424bc000000 } // n = 6, score = 200 // 8b9424b4000000 | mov edx, dword ptr [esp + 0xb4] // 0301 | add eax, dword ptr [ecx] // 895008 | mov dword ptr [eax + 8], edx // 8b9424b8000000 | mov edx, dword ptr [esp + 0xb8] // 89500c | mov dword ptr [eax + 0xc], edx // 8b9424bc000000 | mov edx, dword ptr [esp + 0xbc] $sequence_1 = { 891424 89ca 8b4d84 e8???????? 8b5304 83ec04 85d2 } // n = 7, score = 200 // 891424 | mov dword ptr [esp], edx // 89ca | mov edx, ecx // 8b4d84 | mov ecx, dword ptr [ebp - 0x7c] // e8???????? | // 8b5304 | mov edx, dword ptr [ebx + 4] // 83ec04 | sub esp, 4 // 85d2 | test edx, edx $sequence_2 = { 898538fcffff e8???????? 8b8538fcffff 0fb6440708 88441e08 83c301 } // n = 6, score = 200 // 898538fcffff | mov dword ptr [ebp - 0x3c8], eax // e8???????? | // 8b8538fcffff | mov eax, dword ptr [ebp - 0x3c8] // 0fb6440708 | movzx eax, byte ptr [edi + eax + 8] // 88441e08 | mov byte ptr [esi + ebx + 8], al // 83c301 | add ebx, 1 $sequence_3 = { 8b5c2444 8b7c2440 83fbff 0f84a4000000 39fb 7c4c 85c9 } // n = 7, score = 200 // 8b5c2444 | mov ebx, dword ptr [esp + 0x44] // 8b7c2440 | mov edi, dword ptr [esp + 0x40] // 83fbff | cmp ebx, -1 // 0f84a4000000 | je 0xaa // 39fb | cmp ebx, edi // 7c4c | jl 0x4e // 85c9 | test ecx, ecx $sequence_4 = { e8???????? 0fb6541e08 8d4a9f 89d0 83ea20 80f91a 0f42c2 } // n = 7, score = 200 // e8???????? | // 0fb6541e08 | movzx edx, byte ptr [esi + ebx + 8] // 8d4a9f | lea ecx, [edx - 0x61] // 89d0 | mov eax, edx // 83ea20 | sub edx, 0x20 // 80f91a | cmp cl, 0x1a // 0f42c2 | cmovb eax, edx $sequence_5 = { 0f8697020000 8db600000000 893e 8b07 ba5c5c0000 8d440708 668910 } // n = 7, score = 200 // 0f8697020000 | jbe 0x29d // 8db600000000 | lea esi, [esi] // 893e | mov dword ptr [esi], edi // 8b07 | mov eax, dword ptr [edi] // ba5c5c0000 | mov edx, 0x5c5c // 8d440708 | lea eax, [edi + eax + 8] // 668910 | mov word ptr [eax], dx $sequence_6 = { 31db 01d8 0fb6c9 11f2 89c3 89fe 894c2420 } // n = 7, score = 200 // 31db | xor ebx, ebx // 01d8 | add eax, ebx // 0fb6c9 | movzx ecx, cl // 11f2 | adc edx, esi // 89c3 | mov ebx, eax // 89fe | mov esi, edi // 894c2420 | mov dword ptr [esp + 0x20], ecx $sequence_7 = { 0f8066170000 29df 7105 e8???????? 83c701 0f805e170000 85ff } // n = 7, score = 200 // 0f8066170000 | jo 0x176c // 29df | sub edi, ebx // 7105 | jno 7 // e8???????? | // 83c701 | add edi, 1 // 0f805e170000 | jo 0x1764 // 85ff | test edi, edi $sequence_8 = { 8b39 8b2f 83fd07 775a 8b4c241c 8d4c0aec } // n = 6, score = 200 // 8b39 | mov edi, dword ptr [ecx] // 8b2f | mov ebp, dword ptr [edi] // 83fd07 | cmp ebp, 7 // 775a | ja 0x5c // 8b4c241c | mov ecx, dword ptr [esp + 0x1c] // 8d4c0aec | lea ecx, [edx + ecx - 0x14] $sequence_9 = { 7d49 39e8 0f8670020000 807c1f085c 753a 89dd 83c501 } // n = 7, score = 200 // 7d49 | jge 0x4b // 39e8 | cmp eax, ebp // 0f8670020000 | jbe 0x276 // 807c1f085c | cmp byte ptr [edi + ebx + 8], 0x5c // 753a | jne 0x3c // 89dd | mov ebp, ebx // 83c501 | add ebp, 1 condition: 7 of them and filesize < 1238016 }
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