Actor(s): Lazarus Group
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rule win_bistromath_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-01-25" version = "1" description = "Detects win.bistromath." 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.bistromath" 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 = { e8???????? 6a00 6a06 8d55e8 c745e800000000 8bcb e8???????? } // n = 7, score = 400 // e8???????? | // 6a00 | push 0 // 6a06 | push 6 // 8d55e8 | lea edx, [ebp - 0x18] // c745e800000000 | mov dword ptr [ebp - 0x18], 0 // 8bcb | mov ecx, ebx // e8???????? | $sequence_1 = { ff942470030000 48 89442428 48 8d8c24c0000000 ff942470030000 48 } // n = 7, score = 400 // ff942470030000 | call dword ptr [esp + 0x370] // 48 | dec eax // 89442428 | mov dword ptr [esp + 0x28], eax // 48 | dec eax // 8d8c24c0000000 | lea ecx, [esp + 0xc0] // ff942470030000 | call dword ptr [esp + 0x370] // 48 | dec eax $sequence_2 = { 8b3b 85d2 7471 0fb602 83f826 7462 3d9d000000 } // n = 7, score = 400 // 8b3b | mov edi, dword ptr [ebx] // 85d2 | test edx, edx // 7471 | je 0x73 // 0fb602 | movzx eax, byte ptr [edx] // 83f826 | cmp eax, 0x26 // 7462 | je 0x64 // 3d9d000000 | cmp eax, 0x9d $sequence_3 = { e8???????? 85c0 7407 ba01000000 eb3c 8b442444 ff431c } // n = 7, score = 400 // e8???????? | // 85c0 | test eax, eax // 7407 | je 9 // ba01000000 | mov edx, 1 // eb3c | jmp 0x3e // 8b442444 | mov eax, dword ptr [esp + 0x44] // ff431c | inc dword ptr [ebx + 0x1c] $sequence_4 = { f6c203 7504 33c9 eb05 b901000000 85c9 ba???????? } // n = 7, score = 400 // f6c203 | test dl, 3 // 7504 | jne 6 // 33c9 | xor ecx, ecx // eb05 | jmp 7 // b901000000 | mov ecx, 1 // 85c9 | test ecx, ecx // ba???????? | $sequence_5 = { 394814 0f8eba010000 894c2438 894c243c 8b450c 85c0 7409 } // n = 7, score = 400 // 394814 | cmp dword ptr [eax + 0x14], ecx // 0f8eba010000 | jle 0x1c0 // 894c2438 | mov dword ptr [esp + 0x38], ecx // 894c243c | mov dword ptr [esp + 0x3c], ecx // 8b450c | mov eax, dword ptr [ebp + 0xc] // 85c0 | test eax, eax // 7409 | je 0xb $sequence_6 = { 8b8548ffffff 894624 8b8544ffffff 66894616 8b8540ffffff 5f 66894628 } // n = 7, score = 400 // 8b8548ffffff | mov eax, dword ptr [ebp - 0xb8] // 894624 | mov dword ptr [esi + 0x24], eax // 8b8544ffffff | mov eax, dword ptr [ebp - 0xbc] // 66894616 | mov word ptr [esi + 0x16], ax // 8b8540ffffff | mov eax, dword ptr [ebp - 0xc0] // 5f | pop edi // 66894628 | mov word ptr [esi + 0x28], ax $sequence_7 = { eb0b 85db 0f84bd000000 8b45f4 8b08 33db 85c9 } // n = 7, score = 400 // eb0b | jmp 0xd // 85db | test ebx, ebx // 0f84bd000000 | je 0xc3 // 8b45f4 | mov eax, dword ptr [ebp - 0xc] // 8b08 | mov ecx, dword ptr [eax] // 33db | xor ebx, ebx // 85c9 | test ecx, ecx $sequence_8 = { c3 8b4f44 e8???????? 8bd8 85db 7510 8b4738 } // n = 7, score = 400 // c3 | ret // 8b4f44 | mov ecx, dword ptr [edi + 0x44] // e8???????? | // 8bd8 | mov ebx, eax // 85db | test ebx, ebx // 7510 | jne 0x12 // 8b4738 | mov eax, dword ptr [edi + 0x38] $sequence_9 = { c3 8bce 895e14 e8???????? 8b07 8b4064 394618 } // n = 7, score = 400 // c3 | ret // 8bce | mov ecx, esi // 895e14 | mov dword ptr [esi + 0x14], ebx // e8???????? | // 8b07 | mov eax, dword ptr [edi] // 8b4064 | mov eax, dword ptr [eax + 0x64] // 394618 | cmp dword ptr [esi + 0x18], eax condition: 7 of them and filesize < 33816576 }
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