Actor(s): Turla
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rule win_outlook_backdoor_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-07-11" version = "1" description = "Detects win.outlook_backdoor." 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.outlook_backdoor" malpedia_rule_date = "20230705" malpedia_hash = "42d0574f4405bd7d2b154d321d345acb18834a41" malpedia_version = "20230715" 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 = { 83c40c 8d5c0302 6a00 6a01 8d4dd4 e8???????? 8bc3 } // n = 7, score = 600 // 83c40c | add esp, 0xc // 8d5c0302 | lea ebx, [ebx + eax + 2] // 6a00 | push 0 // 6a01 | push 1 // 8d4dd4 | lea ecx, [ebp - 0x2c] // e8???????? | // 8bc3 | mov eax, ebx $sequence_1 = { 8b01 83c410 ff5004 6a01 884518 ff7518 8d75cc } // n = 7, score = 600 // 8b01 | mov eax, dword ptr [ecx] // 83c410 | add esp, 0x10 // ff5004 | call dword ptr [eax + 4] // 6a01 | push 1 // 884518 | mov byte ptr [ebp + 0x18], al // ff7518 | push dword ptr [ebp + 0x18] // 8d75cc | lea esi, [ebp - 0x34] $sequence_2 = { 8a06 84c0 75df 803e00 0f842e010000 46 c645f400 } // n = 7, score = 600 // 8a06 | mov al, byte ptr [esi] // 84c0 | test al, al // 75df | jne 0xffffffe1 // 803e00 | cmp byte ptr [esi], 0 // 0f842e010000 | je 0x134 // 46 | inc esi // c645f400 | mov byte ptr [ebp - 0xc], 0 $sequence_3 = { 68000000c0 50 ff15???????? 83f8ff 8906 0f95c0 c3 } // n = 7, score = 600 // 68000000c0 | push 0xc0000000 // 50 | push eax // ff15???????? | // 83f8ff | cmp eax, -1 // 8906 | mov dword ptr [esi], eax // 0f95c0 | setne al // c3 | ret $sequence_4 = { ff7508 ff75ec 51 52 e8???????? 8b5e08 8b4e04 } // n = 7, score = 600 // ff7508 | push dword ptr [ebp + 8] // ff75ec | push dword ptr [ebp - 0x14] // 51 | push ecx // 52 | push edx // e8???????? | // 8b5e08 | mov ebx, dword ptr [esi + 8] // 8b4e04 | mov ecx, dword ptr [esi + 4] $sequence_5 = { ff7508 e8???????? 8b4df4 b001 5b 64890d00000000 c9 } // n = 7, score = 600 // ff7508 | push dword ptr [ebp + 8] // e8???????? | // 8b4df4 | mov ecx, dword ptr [ebp - 0xc] // b001 | mov al, 1 // 5b | pop ebx // 64890d00000000 | mov dword ptr fs:[0], ecx // c9 | leave $sequence_6 = { ff5744 8bf0 e8???????? 5f 5e c20400 55 } // n = 7, score = 600 // ff5744 | call dword ptr [edi + 0x44] // 8bf0 | mov esi, eax // e8???????? | // 5f | pop edi // 5e | pop esi // c20400 | ret 4 // 55 | push ebp $sequence_7 = { e8???????? 83ec20 8365f000 56 8bf1 6a00 8d4dd4 } // n = 7, score = 600 // e8???????? | // 83ec20 | sub esp, 0x20 // 8365f000 | and dword ptr [ebp - 0x10], 0 // 56 | push esi // 8bf1 | mov esi, ecx // 6a00 | push 0 // 8d4dd4 | lea ecx, [ebp - 0x2c] $sequence_8 = { 50 56 53 53 ff15???????? ff742410 8d4c2420 } // n = 7, score = 600 // 50 | push eax // 56 | push esi // 53 | push ebx // 53 | push ebx // ff15???????? | // ff742410 | push dword ptr [esp + 0x10] // 8d4c2420 | lea ecx, [esp + 0x20] $sequence_9 = { ff750c e8???????? 83c40c 85c0 7517 8b45fc 0fb61c18 } // n = 7, score = 600 // ff750c | push dword ptr [ebp + 0xc] // e8???????? | // 83c40c | add esp, 0xc // 85c0 | test eax, eax // 7517 | jne 0x19 // 8b45fc | mov eax, dword ptr [ebp - 4] // 0fb61c18 | movzx ebx, byte ptr [eax + ebx] condition: 7 of them and filesize < 2912256 }
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