Ransomware overwriting the system's MBR, making it impossible to boot into Windows.
rule win_mbrlocker_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-01-25" version = "1" description = "Detects win.mbrlocker." 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.mbrlocker" 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 = { 89f7 8b4d10 8b550c ac 30c8 } // n = 5, score = 100 // 89f7 | mov edi, esi // 8b4d10 | mov ecx, dword ptr [ebp + 0x10] // 8b550c | mov edx, dword ptr [ebp + 0xc] // ac | lodsb al, byte ptr [esi] // 30c8 | xor al, cl $sequence_1 = { 68fe000000 68???????? ffd7 83c408 } // n = 4, score = 100 // 68fe000000 | push 0xfe // 68???????? | // ffd7 | call edi // 83c408 | add esp, 8 $sequence_2 = { 8b7508 89f7 8b4d10 8b550c ac 30c8 } // n = 6, score = 100 // 8b7508 | mov esi, dword ptr [ebp + 8] // 89f7 | mov edi, esi // 8b4d10 | mov ecx, dword ptr [ebp + 0x10] // 8b550c | mov edx, dword ptr [ebp + 0xc] // ac | lodsb al, byte ptr [esi] // 30c8 | xor al, cl $sequence_3 = { 89e5 60 8b7508 89f7 8b4d10 } // n = 5, score = 100 // 89e5 | mov ebp, esp // 60 | pushal // 8b7508 | mov esi, dword ptr [ebp + 8] // 89f7 | mov edi, esi // 8b4d10 | mov ecx, dword ptr [ebp + 0x10] $sequence_4 = { 68???????? ffd6 83c408 68ff000000 68fe000000 } // n = 5, score = 100 // 68???????? | // ffd6 | call esi // 83c408 | add esp, 8 // 68ff000000 | push 0xff // 68fe000000 | push 0xfe $sequence_5 = { ff750c ff7508 68???????? ff25???????? } // n = 4, score = 100 // ff750c | push dword ptr [ebp + 0xc] // ff7508 | push dword ptr [ebp + 8] // 68???????? | // ff25???????? | $sequence_6 = { 31c8 e8???????? 68ac000000 68???????? ffd6 83c408 68ff000000 } // n = 7, score = 100 // 31c8 | xor eax, ecx // e8???????? | // 68ac000000 | push 0xac // 68???????? | // ffd6 | call esi // 83c408 | add esp, 8 // 68ff000000 | push 0xff $sequence_7 = { 83c408 68ff000000 68fe000000 68???????? e8???????? } // n = 5, score = 100 // 83c408 | add esp, 8 // 68ff000000 | push 0xff // 68fe000000 | push 0xfe // 68???????? | // e8???????? | $sequence_8 = { 68fe000000 68???????? e8???????? e8???????? 68ff000000 68fe000000 } // n = 6, score = 100 // 68fe000000 | push 0xfe // 68???????? | // e8???????? | // e8???????? | // 68ff000000 | push 0xff // 68fe000000 | push 0xfe $sequence_9 = { 58 e8???????? 751e 6a10 } // n = 4, score = 100 // 58 | pop eax // e8???????? | // 751e | jne 0x20 // 6a10 | push 0x10 condition: 7 of them and filesize < 43008 }
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