A variant of CryptoMix is win.clop.
rule win_cryptomix_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-12-06" version = "1" description = "Detects win.cryptomix." 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.cryptomix" 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 = { c3 68f0767c2a 6a04 e8???????? 59 59 } // n = 6, score = 200 // c3 | ret // 68f0767c2a | push 0x2a7c76f0 // 6a04 | push 4 // e8???????? | // 59 | pop ecx // 59 | pop ecx $sequence_1 = { 02f8 0fb6cf 8d7601 0fb60439 8846ff 881439 33c9 } // n = 7, score = 200 // 02f8 | add bh, al // 0fb6cf | movzx ecx, bh // 8d7601 | lea esi, [esi + 1] // 0fb60439 | movzx eax, byte ptr [ecx + edi] // 8846ff | mov byte ptr [esi - 1], al // 881439 | mov byte ptr [ecx + edi], dl // 33c9 | xor ecx, ecx $sequence_2 = { e8???????? 59 eb03 8b5df0 ff75f8 e8???????? } // n = 6, score = 200 // e8???????? | // 59 | pop ecx // eb03 | jmp 5 // 8b5df0 | mov ebx, dword ptr [ebp - 0x10] // ff75f8 | push dword ptr [ebp - 8] // e8???????? | $sequence_3 = { 7504 6a08 eb35 83f804 } // n = 4, score = 200 // 7504 | jne 6 // 6a08 | push 8 // eb35 | jmp 0x37 // 83f804 | cmp eax, 4 $sequence_4 = { ff4d08 8b4dfc 8ad8 75cc 5f } // n = 5, score = 200 // ff4d08 | dec dword ptr [ebp + 8] // 8b4dfc | mov ecx, dword ptr [ebp - 4] // 8ad8 | mov bl, al // 75cc | jne 0xffffffce // 5f | pop edi $sequence_5 = { 59 59 ffd0 83f87a 7413 56 57 } // n = 7, score = 200 // 59 | pop ecx // 59 | pop ecx // ffd0 | call eax // 83f87a | cmp eax, 0x7a // 7413 | je 0x15 // 56 | push esi // 57 | push edi $sequence_6 = { 56 683f000f00 56 56 56 53 57 } // n = 7, score = 200 // 56 | push esi // 683f000f00 | push 0xf003f // 56 | push esi // 56 | push esi // 56 | push esi // 53 | push ebx // 57 | push edi $sequence_7 = { ffd0 c3 686ea4ffa5 6a05 } // n = 4, score = 200 // ffd0 | call eax // c3 | ret // 686ea4ffa5 | push 0xa5ffa46e // 6a05 | push 5 $sequence_8 = { ffd6 85c0 0f856a010000 68???????? 8d85c4f9ffff } // n = 5, score = 200 // ffd6 | call esi // 85c0 | test eax, eax // 0f856a010000 | jne 0x170 // 68???????? | // 8d85c4f9ffff | lea eax, [ebp - 0x63c] $sequence_9 = { 837d0c01 8bbdb8f9ffff a1???????? 68???????? } // n = 4, score = 200 // 837d0c01 | cmp dword ptr [ebp + 0xc], 1 // 8bbdb8f9ffff | mov edi, dword ptr [ebp - 0x648] // a1???????? | // 68???????? | $sequence_10 = { 68???????? 57 ffd0 ff75fc e8???????? } // n = 5, score = 200 // 68???????? | // 57 | push edi // ffd0 | call eax // ff75fc | push dword ptr [ebp - 4] // e8???????? | $sequence_11 = { 8bf1 6a01 899584efffff 89b58cefffff 898588efffff ff15???????? 6808020000 } // n = 7, score = 200 // 8bf1 | mov esi, ecx // 6a01 | push 1 // 899584efffff | mov dword ptr [ebp - 0x107c], edx // 89b58cefffff | mov dword ptr [ebp - 0x1074], esi // 898588efffff | mov dword ptr [ebp - 0x1078], eax // ff15???????? | // 6808020000 | push 0x208 $sequence_12 = { 8d85c4f9ffff 50 ffd7 85c0 7460 68???????? } // n = 6, score = 200 // 8d85c4f9ffff | lea eax, [ebp - 0x63c] // 50 | push eax // ffd7 | call edi // 85c0 | test eax, eax // 7460 | je 0x62 // 68???????? | $sequence_13 = { 8b35???????? 68007d0000 6a40 c745f8e8030000 } // n = 4, score = 200 // 8b35???????? | // 68007d0000 | push 0x7d00 // 6a40 | push 0x40 // c745f8e8030000 | mov dword ptr [ebp - 8], 0x3e8 $sequence_14 = { 6a00 6a00 ff15???????? 6896000000 ff15???????? 8b9d80efffff 8d8598f9ffff } // n = 7, score = 200 // 6a00 | push 0 // 6a00 | push 0 // ff15???????? | // 6896000000 | push 0x96 // ff15???????? | // 8b9d80efffff | mov ebx, dword ptr [ebp - 0x1080] // 8d8598f9ffff | lea eax, [ebp - 0x668] $sequence_15 = { 68???????? 56 e8???????? 59 59 85c0 7759 } // n = 7, score = 200 // 68???????? | // 56 | push esi // e8???????? | // 59 | pop ecx // 59 | pop ecx // 85c0 | test eax, eax // 7759 | ja 0x5b condition: 7 of them and filesize < 188416 }
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