Actor(s): HAZY TIGER
Cisco Talos attributes this backdoor with moderate confidence to the Bitter APT.
rule win_zxxz_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2023-03-28" version = "1" description = "Detects win.zxxz." 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.zxxz" malpedia_rule_date = "20230328" malpedia_hash = "9d2d75cef573c1c2d861f5197df8f563b05a305d" malpedia_version = "20230407" 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 = { 68???????? ffd6 83c40c 33c0 } // n = 4, score = 100 // 68???????? | // ffd6 | call esi // 83c40c | add esp, 0xc // 33c0 | xor eax, eax $sequence_1 = { 740b 8a81315c4000 41 84c0 75f1 8a81315c4000 } // n = 6, score = 100 // 740b | je 0xd // 8a81315c4000 | mov al, byte ptr [ecx + 0x405c31] // 41 | inc ecx // 84c0 | test al, al // 75f1 | jne 0xfffffff3 // 8a81315c4000 | mov al, byte ptr [ecx + 0x405c31] $sequence_2 = { 40 84c9 75f9 2bc2 8b54240c 50 68???????? } // n = 7, score = 100 // 40 | inc eax // 84c9 | test cl, cl // 75f9 | jne 0xfffffffb // 2bc2 | sub eax, edx // 8b54240c | mov edx, dword ptr [esp + 0xc] // 50 | push eax // 68???????? | $sequence_3 = { 51 68???????? e8???????? 8d842414020000 83c40c 8d5001 } // n = 6, score = 100 // 51 | push ecx // 68???????? | // e8???????? | // 8d842414020000 | lea eax, [esp + 0x214] // 83c40c | add esp, 0xc // 8d5001 | lea edx, [eax + 1] $sequence_4 = { 33c0 e9???????? 68???????? 8d4c2414 68fa000000 51 } // n = 6, score = 100 // 33c0 | xor eax, eax // e9???????? | // 68???????? | // 8d4c2414 | lea ecx, [esp + 0x14] // 68fa000000 | push 0xfa // 51 | push ecx $sequence_5 = { a1???????? 33c4 89442434 55 56 57 } // n = 6, score = 100 // a1???????? | // 33c4 | xor eax, esp // 89442434 | mov dword ptr [esp + 0x34], eax // 55 | push ebp // 56 | push esi // 57 | push edi $sequence_6 = { 68???????? c705????????524e4700 ffd6 83c40c 68???????? } // n = 5, score = 100 // 68???????? | // c705????????524e4700 | // ffd6 | call esi // 83c40c | add esp, 0xc // 68???????? | $sequence_7 = { 6a00 6a00 6a15 6a00 ffd6 85c0 743d } // n = 7, score = 100 // 6a00 | push 0 // 6a00 | push 0 // 6a15 | push 0x15 // 6a00 | push 0 // ffd6 | call esi // 85c0 | test eax, eax // 743d | je 0x3f $sequence_8 = { 51 68???????? e8???????? 8d842414020000 } // n = 4, score = 100 // 51 | push ecx // 68???????? | // e8???????? | // 8d842414020000 | lea eax, [esp + 0x214] $sequence_9 = { 50 6a00 6a00 6a15 6a00 ffd6 } // n = 6, score = 100 // 50 | push eax // 6a00 | push 0 // 6a00 | push 0 // 6a15 | push 0x15 // 6a00 | push 0 // ffd6 | call esi condition: 7 of them and filesize < 4142080 }
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