Actor(s): Turla Group
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rule win_outlook_backdoor_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2020-12-22" version = "1" description = "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 = "20201222" malpedia_hash = "30354d830a29f0fbd3714d93d94dea941d77a130" malpedia_version = "20201023" 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 = { 2bd1 50 8955e4 894de0 e8???????? 85c0 7404 } // n = 7, score = 600 // 2bd1 | sub edx, ecx // 50 | push eax // 8955e4 | mov dword ptr [ebp - 0x1c], edx // 894de0 | mov dword ptr [ebp - 0x20], ecx // e8???????? | // 85c0 | test eax, eax // 7404 | je 6 $sequence_1 = { eb02 33f6 834dfcff 85c0 7406 } // n = 5, score = 600 // eb02 | jmp 4 // 33f6 | xor esi, esi // 834dfcff | or dword ptr [ebp - 4], 0xffffffff // 85c0 | test eax, eax // 7406 | je 8 $sequence_2 = { e8???????? 59 8bc6 5e c20400 8325????????00 53 } // n = 7, score = 600 // e8???????? | // 59 | pop ecx // 8bc6 | mov eax, esi // 5e | pop esi // c20400 | ret 4 // 8325????????00 | // 53 | push ebx $sequence_3 = { ff742420 ff15???????? 8bf0 e8???????? 8b35???????? 8d442418 50 } // n = 7, score = 600 // ff742420 | push dword ptr [esp + 0x20] // ff15???????? | // 8bf0 | mov esi, eax // e8???????? | // 8b35???????? | // 8d442418 | lea eax, [esp + 0x18] // 50 | push eax $sequence_4 = { ff5038 8bf0 e8???????? 680201ff0f 8bc3 e8???????? 8b4df4 } // n = 7, score = 600 // ff5038 | call dword ptr [eax + 0x38] // 8bf0 | mov esi, eax // e8???????? | // 680201ff0f | push 0xfff0102 // 8bc3 | mov eax, ebx // e8???????? | // 8b4df4 | mov ecx, dword ptr [ebp - 0xc] $sequence_5 = { 7604 2bc1 8bf0 85d2 7416 85f6 7412 } // n = 7, score = 600 // 7604 | jbe 6 // 2bc1 | sub eax, ecx // 8bf0 | mov esi, eax // 85d2 | test edx, edx // 7416 | je 0x18 // 85f6 | test esi, esi // 7412 | je 0x14 $sequence_6 = { 50 8d442424 e8???????? c68424ac00000001 } // n = 4, score = 600 // 50 | push eax // 8d442424 | lea eax, [esp + 0x24] // e8???????? | // c68424ac00000001 | mov byte ptr [esp + 0xac], 1 $sequence_7 = { 3b4510 7333 8b4718 8d4f04 83f810 7204 } // n = 6, score = 600 // 3b4510 | cmp eax, dword ptr [ebp + 0x10] // 7333 | jae 0x35 // 8b4718 | mov eax, dword ptr [edi + 0x18] // 8d4f04 | lea ecx, [edi + 4] // 83f810 | cmp eax, 0x10 // 7204 | jb 6 $sequence_8 = { e9???????? 56 6a01 8d4c2434 e8???????? 56 6a01 } // n = 7, score = 600 // e9???????? | // 56 | push esi // 6a01 | push 1 // 8d4c2434 | lea ecx, [esp + 0x34] // e8???????? | // 56 | push esi // 6a01 | push 1 $sequence_9 = { e9???????? ff75f0 e8???????? c3 8b45f0 83c018 e9???????? } // n = 7, score = 600 // e9???????? | // ff75f0 | push dword ptr [ebp - 0x10] // e8???????? | // c3 | ret // 8b45f0 | mov eax, dword ptr [ebp - 0x10] // 83c018 | add eax, 0x18 // e9???????? | condition: 7 of them and filesize < 2912256 }
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