Information Stealer that searches for sensitive documents and uploads its results to an FTP server. Skips files with known Ryuk extensions.
rule win_ryuk_stealer_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-01-25" version = "1" description = "Detects win.ryuk_stealer." 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.ryuk_stealer" 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 = { 6bc064 05???????? 50 8d85b4fdffff } // n = 4, score = 800 // 6bc064 | imul eax, eax, 0x64 // 05???????? | // 50 | push eax // 8d85b4fdffff | lea eax, [ebp - 0x24c] $sequence_1 = { 8d85b4fdffff 6a2e 50 e8???????? } // n = 4, score = 800 // 8d85b4fdffff | lea eax, [ebp - 0x24c] // 6a2e | push 0x2e // 50 | push eax // e8???????? | $sequence_2 = { 8bc8 33d2 8bc6 f7f1 6a0a } // n = 5, score = 800 // 8bc8 | mov ecx, eax // 33d2 | xor edx, edx // 8bc6 | mov eax, esi // f7f1 | div ecx // 6a0a | push 0xa $sequence_3 = { 8a443706 3c2f 7404 3c2d } // n = 4, score = 800 // 8a443706 | mov al, byte ptr [edi + esi + 6] // 3c2f | cmp al, 0x2f // 7404 | je 6 // 3c2d | cmp al, 0x2d $sequence_4 = { b910270000 f7f1 8bf2 e8???????? 8bc8 33d2 8bc6 } // n = 7, score = 800 // b910270000 | mov ecx, 0x2710 // f7f1 | div ecx // 8bf2 | mov esi, edx // e8???????? | // 8bc8 | mov ecx, eax // 33d2 | xor edx, edx // 8bc6 | mov eax, esi $sequence_5 = { 99 b9a0860100 f7f9 81c2a8610000 52 } // n = 5, score = 800 // 99 | cdq // b9a0860100 | mov ecx, 0x186a0 // f7f9 | idiv ecx // 81c2a8610000 | add edx, 0x61a8 // 52 | push edx $sequence_6 = { ff15???????? 83f805 740a b9???????? } // n = 4, score = 800 // ff15???????? | // 83f805 | cmp eax, 5 // 740a | je 0xc // b9???????? | $sequence_7 = { f7f9 81c2a8610000 52 ff15???????? } // n = 4, score = 800 // f7f9 | idiv ecx // 81c2a8610000 | add edx, 0x61a8 // 52 | push edx // ff15???????? | $sequence_8 = { ff15???????? 33ff 0fb60437 50 } // n = 4, score = 800 // ff15???????? | // 33ff | xor edi, edi // 0fb60437 | movzx eax, byte ptr [edi + esi] // 50 | push eax $sequence_9 = { 83f801 7410 83ff01 755d } // n = 4, score = 800 // 83f801 | cmp eax, 1 // 7410 | je 0x12 // 83ff01 | cmp edi, 1 // 755d | jne 0x5f condition: 7 of them and filesize < 368640 }
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