Actor(s): Earth Lusca
A custom loader for CobaltStrike.
rule win_fishmaster_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2026-01-05" version = "1" description = "Detects win.fishmaster." 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.fishmaster" malpedia_rule_date = "20260105" malpedia_hash = "19b79e7cab4eaf532122e5b45a77dd8f6bb5cc79" malpedia_version = "20251219" 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 = { b9e8030000 ff15???????? 4c89742450 48c74424580f000000 } // n = 4, score = 100 // b9e8030000 | mov dword ptr [ebp + 8], eax // ff15???????? | // 4c89742450 | dec eax // 48c74424580f000000 | lea eax, [ebp + 0xbf0] $sequence_1 = { 8d45fd 4863c8 460fbe0401 418d40bf 3c19 7706 } // n = 6, score = 100 // 8d45fd | lea ecx, [eax - 0x60] // 4863c8 | dec eax // 460fbe0401 | mov dword ptr [ebx + 0x10], esi // 418d40bf | dec eax // 3c19 | mov dword ptr [ebx + 0x18], 0xf // 7706 | inc eax $sequence_2 = { 7203 4c8b03 8d45ff 4863c8 } // n = 4, score = 100 // 7203 | nop // 4c8b03 | dec ecx // 8d45ff | cmp esi, 0x10 // 4863c8 | dec eax $sequence_3 = { 488d0d25310000 0f57c0 488d5308 48890b 488d4808 0f1102 ff15???????? } // n = 7, score = 100 // 488d0d25310000 | cmp al, 9 // 0f57c0 | ja 0xac9 // 488d5308 | inc esp // 48890b | lea edi, [ecx + 4] // 488d4808 | jmp 0xada // 0f1102 | inc esp // ff15???????? | $sequence_4 = { 488bcb 41ffd5 90 488b5558 4883fa10 7234 } // n = 6, score = 100 // 488bcb | mov eax, dword ptr [ebx] // 41ffd5 | lea eax, [ebp - 1] // 90 | inc ecx // 488b5558 | cmove ebp, edx // 4883fa10 | mov ecx, ebp // 7234 | sar ecx, 4 $sequence_5 = { ba05000020 488bcb ff15???????? 488bcb ff15???????? c744243000010000 } // n = 6, score = 100 // ba05000020 | mov dword ptr [esp + 0xa8], 2 // 488bcb | jmp 0xe00 // ff15???????? | // 488bcb | dec eax // ff15???????? | // c744243000010000 | mov ecx, ebx $sequence_6 = { 488d054d2a0000 c3 8325????????00 c3 48895c2408 55 } // n = 6, score = 100 // 488d054d2a0000 | inc ecx // c3 | cmp al, 0x2f // 8325????????00 | // c3 | inc ecx // 48895c2408 | cmove edi, edi // 55 | sar edi, 2 $sequence_7 = { 4983f910 7203 4c8b03 8d45ff 4863c8 460fbe0401 418d40bf } // n = 7, score = 100 // 4983f910 | lea ecx, [eax + 0x27] // 7203 | dec eax // 4c8b03 | cmp ecx, eax // 8d45ff | jbe 0x8ef // 4863c8 | jmp 0x802 // 460fbe0401 | dec eax // 418d40bf | mov ecx, 0x27 $sequence_8 = { 83f828 7309 33c9 ff15???????? cc } // n = 5, score = 100 // 83f828 | mov ecx, dword ptr [ebx + 0x10] // 7309 | dec eax // 33c9 | movsx ecx, byte ptr [ecx] // ff15???????? | // cc | and ecx, 3 $sequence_9 = { 4883f801 721c 488d4101 48894310 4883fa10 488bc3 7203 } // n = 7, score = 100 // 4883f801 | lea eax, [ecx - 0x30] // 721c | cmp al, 9 // 488d4101 | ja 0x2b5 // 48894310 | cmp al, 0x19 // 4883fa10 | ja 0x2b9 // 488bc3 | inc esp // 7203 | lea esp, [ecx - 0x41] condition: 7 of them and filesize < 812032 }
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