Actor(s): Turla Group
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rule win_outlook_backdoor_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2022-04-08" 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 = "20220405" malpedia_hash = "ecd38294bd47d5589be5cd5490dc8bb4804afc2a" malpedia_version = "20220411" 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 8945e8 85c0 7503 214520 837dac10 8b4598 } // n = 7, score = 600 // 83c40c | add esp, 0xc // 8945e8 | mov dword ptr [ebp - 0x18], eax // 85c0 | test eax, eax // 7503 | jne 5 // 214520 | and dword ptr [ebp + 0x20], eax // 837dac10 | cmp dword ptr [ebp - 0x54], 0x10 // 8b4598 | mov eax, dword ptr [ebp - 0x68] $sequence_1 = { 8d4608 6a00 6880000000 6a02 6a00 6a01 68000000c0 } // n = 7, score = 600 // 8d4608 | lea eax, dword ptr [esi + 8] // 6a00 | push 0 // 6880000000 | push 0x80 // 6a02 | push 2 // 6a00 | push 0 // 6a01 | push 1 // 68000000c0 | push 0xc0000000 $sequence_2 = { 8b4704 894004 83670800 3b5f04 741c 55 56 } // n = 7, score = 600 // 8b4704 | mov eax, dword ptr [edi + 4] // 894004 | mov dword ptr [eax + 4], eax // 83670800 | and dword ptr [edi + 8], 0 // 3b5f04 | cmp ebx, dword ptr [edi + 4] // 741c | je 0x1e // 55 | push ebp // 56 | push esi $sequence_3 = { ff7528 ff75dc ff7524 50 8b4514 e8???????? 8b08 } // n = 7, score = 600 // ff7528 | push dword ptr [ebp + 0x28] // ff75dc | push dword ptr [ebp - 0x24] // ff7524 | push dword ptr [ebp + 0x24] // 50 | push eax // 8b4514 | mov eax, dword ptr [ebp + 0x14] // e8???????? | // 8b08 | mov ecx, dword ptr [eax] $sequence_4 = { 53 ff7004 ff30 53 51 ff5214 8bf0 } // n = 7, score = 600 // 53 | push ebx // ff7004 | push dword ptr [eax + 4] // ff30 | push dword ptr [eax] // 53 | push ebx // 51 | push ecx // ff5214 | call dword ptr [edx + 0x14] // 8bf0 | mov esi, eax $sequence_5 = { 6a00 8d45d0 e8???????? eb16 8b75ec 6aff 6a00 } // n = 7, score = 600 // 6a00 | push 0 // 8d45d0 | lea eax, dword ptr [ebp - 0x30] // e8???????? | // eb16 | jmp 0x18 // 8b75ec | mov esi, dword ptr [ebp - 0x14] // 6aff | push -1 // 6a00 | push 0 $sequence_6 = { 83ec2c 56 57 ff750c 8d7308 ff7508 8b06 } // n = 7, score = 600 // 83ec2c | sub esp, 0x2c // 56 | push esi // 57 | push edi // ff750c | push dword ptr [ebp + 0xc] // 8d7308 | lea esi, dword ptr [ebx + 8] // ff7508 | push dword ptr [ebp + 8] // 8b06 | mov eax, dword ptr [esi] $sequence_7 = { e8???????? 8b4508 83c428 5f 5e 5b 8be5 } // n = 7, score = 600 // e8???????? | // 8b4508 | mov eax, dword ptr [ebp + 8] // 83c428 | add esp, 0x28 // 5f | pop edi // 5e | pop esi // 5b | pop ebx // 8be5 | mov esp, ebp $sequence_8 = { 59 8945ec 8365fc00 33db 43 85c0 7424 } // n = 7, score = 600 // 59 | pop ecx // 8945ec | mov dword ptr [ebp - 0x14], eax // 8365fc00 | and dword ptr [ebp - 4], 0 // 33db | xor ebx, ebx // 43 | inc ebx // 85c0 | test eax, eax // 7424 | je 0x26 $sequence_9 = { 89442410 7e70 0fb640ff 8b17 50 8bcf } // n = 6, score = 600 // 89442410 | mov dword ptr [esp + 0x10], eax // 7e70 | jle 0x72 // 0fb640ff | movzx eax, byte ptr [eax - 1] // 8b17 | mov edx, dword ptr [edi] // 50 | push eax // 8bcf | mov ecx, edi condition: 7 of them and filesize < 2912256 }
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