Actor(s): NARWHAL SPIDER
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rule win_cutwail_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-01-25" version = "1" description = "Detects win.cutwail." 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.cutwail" 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 = { 7e2d 8d7702 8d58ff 8a46ff } // n = 4, score = 200 // 7e2d | jle 0x2f // 8d7702 | lea esi, [edi + 2] // 8d58ff | lea ebx, [eax - 1] // 8a46ff | mov al, byte ptr [esi - 1] $sequence_1 = { 46 40 381e 75f6 a1???????? } // n = 5, score = 200 // 46 | inc esi // 40 | inc eax // 381e | cmp byte ptr [esi], bl // 75f6 | jne 0xfffffff8 // a1???????? | $sequence_2 = { 8338ff 56 7554 83c004 } // n = 4, score = 200 // 8338ff | cmp dword ptr [eax], -1 // 56 | push esi // 7554 | jne 0x56 // 83c004 | add eax, 4 $sequence_3 = { ff7514 ffd6 ff750c ff7514 ffd6 } // n = 5, score = 200 // ff7514 | push dword ptr [ebp + 0x14] // ffd6 | call esi // ff750c | push dword ptr [ebp + 0xc] // ff7514 | push dword ptr [ebp + 0x14] // ffd6 | call esi $sequence_4 = { e8???????? 03c3 6a73 8d4dee } // n = 4, score = 200 // e8???????? | // 03c3 | add eax, ebx // 6a73 | push 0x73 // 8d4dee | lea ecx, [ebp - 0x12] $sequence_5 = { 3bfb 7511 33d2 3bc3 } // n = 4, score = 200 // 3bfb | cmp edi, ebx // 7511 | jne 0x13 // 33d2 | xor edx, edx // 3bc3 | cmp eax, ebx $sequence_6 = { 894528 0f842a020000 68dc000000 8d4d88 } // n = 4, score = 200 // 894528 | mov dword ptr [ebp + 0x28], eax // 0f842a020000 | je 0x230 // 68dc000000 | push 0xdc // 8d4d88 | lea ecx, [ebp - 0x78] $sequence_7 = { 33c0 eb11 53 ff15???????? 8b4514 } // n = 5, score = 200 // 33c0 | xor eax, eax // eb11 | jmp 0x13 // 53 | push ebx // ff15???????? | // 8b4514 | mov eax, dword ptr [ebp + 0x14] condition: 7 of them and filesize < 262144 }
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