This ransomware modifies the master boot record of the victim's computer so that it shows a ransom note before Windows starts.
rule win_mbrlock_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-01-25" version = "1" description = "Detects win.mbrlock." 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.mbrlock" 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 = { 8b4dd0 8bc2 0bc1 0f8450feffff 83c708 83d300 81e100000080 } // n = 7, score = 100 // 8b4dd0 | mov ecx, dword ptr [ebp - 0x30] // 8bc2 | mov eax, edx // 0bc1 | or eax, ecx // 0f8450feffff | je 0xfffffe56 // 83c708 | add edi, 8 // 83d300 | adc ebx, 0 // 81e100000080 | and ecx, 0x80000000 $sequence_1 = { 68a2000000 68804d0110 e8???????? 83c410 8b4508 50 ff15???????? } // n = 7, score = 100 // 68a2000000 | push 0xa2 // 68804d0110 | push 0x10014d80 // e8???????? | // 83c410 | add esp, 0x10 // 8b4508 | mov eax, dword ptr [ebp + 8] // 50 | push eax // ff15???????? | $sequence_2 = { 83c410 8b55ec 8b06 6a00 6a00 52 57 } // n = 7, score = 100 // 83c410 | add esp, 0x10 // 8b55ec | mov edx, dword ptr [ebp - 0x14] // 8b06 | mov eax, dword ptr [esi] // 6a00 | push 0 // 6a00 | push 0 // 52 | push edx // 57 | push edi $sequence_3 = { 8b4518 8b08 8b45d8 3bc8 7319 68fc600110 6a05 } // n = 7, score = 100 // 8b4518 | mov eax, dword ptr [ebp + 0x18] // 8b08 | mov ecx, dword ptr [eax] // 8b45d8 | mov eax, dword ptr [ebp - 0x28] // 3bc8 | cmp ecx, eax // 7319 | jae 0x1b // 68fc600110 | push 0x100160fc // 6a05 | push 5 $sequence_4 = { 83c404 85db 895ddc 7518 68804e0110 50 68fd030000 } // n = 7, score = 100 // 83c404 | add esp, 4 // 85db | test ebx, ebx // 895ddc | mov dword ptr [ebp - 0x24], ebx // 7518 | jne 0x1a // 68804e0110 | push 0x10014e80 // 50 | push eax // 68fd030000 | push 0x3fd $sequence_5 = { ffd7 894618 8b4610 688c500110 50 ffd7 8b4e10 } // n = 7, score = 100 // ffd7 | call edi // 894618 | mov dword ptr [esi + 0x18], eax // 8b4610 | mov eax, dword ptr [esi + 0x10] // 688c500110 | push 0x1001508c // 50 | push eax // ffd7 | call edi // 8b4e10 | mov ecx, dword ptr [esi + 0x10] $sequence_6 = { 6858190110 51 c745e401000000 e8???????? 8b03 8b4004 83f8ff } // n = 7, score = 100 // 6858190110 | push 0x10011958 // 51 | push ecx // c745e401000000 | mov dword ptr [ebp - 0x1c], 1 // e8???????? | // 8b03 | mov eax, dword ptr [ebx] // 8b4004 | mov eax, dword ptr [eax + 4] // 83f8ff | cmp eax, -1 $sequence_7 = { 894508 e9???????? 8b8bd4030000 c1e102 51 e8???????? 33f6 } // n = 7, score = 100 // 894508 | mov dword ptr [ebp + 8], eax // e9???????? | // 8b8bd4030000 | mov ecx, dword ptr [ebx + 0x3d4] // c1e102 | shl ecx, 2 // 51 | push ecx // e8???????? | // 33f6 | xor esi, esi $sequence_8 = { eb0f e8???????? 83f803 7405 e8???????? f6c308 7432 } // n = 7, score = 100 // eb0f | jmp 0x11 // e8???????? | // 83f803 | cmp eax, 3 // 7405 | je 7 // e8???????? | // f6c308 | test bl, 8 // 7432 | je 0x34 $sequence_9 = { 8b4608 5f 5e 5b c3 8bc7 5f } // n = 7, score = 100 // 8b4608 | mov eax, dword ptr [esi + 8] // 5f | pop edi // 5e | pop esi // 5b | pop ebx // c3 | ret // 8bc7 | mov eax, edi // 5f | pop edi condition: 7 of them and filesize < 2031616 }
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