rule win_skipper_auto { meta: author = "Felix Bilstein - yara-signator at cocacoding dot com" date = "2026-09-17" version = "1" description = "Detects win.skipper." 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.skipper" malpedia_rule_date = "20260916" malpedia_hash = "53a643781c18e08f4a50949af60172d837a0b6f6" malpedia_version = "20260917" 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 = { 6a03 68???????? 68???????? 6a50 } // n = 4, score = 600 // 6a03 | lea ebp, [0xf005] // 68???????? | // 68???????? | // 6a50 | inc ecx $sequence_1 = { ff15???????? 6a00 6a00 6a00 6a00 68???????? 68???????? } // n = 7, score = 500 // ff15???????? | // 6a00 | push 0x104 // 6a00 | mov eax, dword ptr [ebp - 0x128] // 6a00 | push eax // 6a00 | cmp eax, 0x100 // 68???????? | // 68???????? | $sequence_2 = { e8???????? 6804010000 e8???????? 6804010000 8bf8 6a00 57 } // n = 7, score = 500 // e8???????? | // 6804010000 | jge 0x17 // e8???????? | // 6804010000 | mov cl, byte ptr [eax + ebx + 0x11d] // 8bf8 | mov byte ptr [eax + 0x23a5b0], cl // 6a00 | inc eax // 57 | jmp 0xfffffff6 $sequence_3 = { 6a00 6a00 6a00 50 ff15???????? 53 8bf0 } // n = 7, score = 400 // 6a00 | push 0 // 6a00 | push edi // 6a00 | push edi // 50 | push 8 // ff15???????? | // 53 | jns 0xa // 8bf0 | dec ecx $sequence_4 = { 83c428 8d4601 90 8a0e } // n = 4, score = 400 // 83c428 | add byte ptr [ebx], ah // 8d4601 | ror dword ptr [edx - 0x75f877fa], 1 // 90 | inc esi // 8a0e | add byte ptr [ebx + edx*2], al $sequence_5 = { b9???????? e8???????? 83c428 53 56 } // n = 5, score = 400 // b9???????? | // e8???????? | // 83c428 | add byte ptr [ebx + edx*2], al // 53 | and eax, dword ptr [eax] // 56 | sub byte ptr [ebx + 0x23], dl $sequence_6 = { 46 8a01 888435fbfeffff 8811 81fe00010000 7cb1 8b750c } // n = 7, score = 400 // 46 | and eax, dword ptr [eax] // 8a01 | sub byte ptr [ebx + 0x23], dl // 888435fbfeffff | add byte ptr [ebx], ah // 8811 | ror dword ptr [edx - 0x75f877fa], 1 // 81fe00010000 | inc esi // 7cb1 | add dword ptr [eax + 0x468a0147], ecx // 8b750c | push eax $sequence_7 = { 57 ff15???????? 6804010000 6a00 57 e8???????? 57 } // n = 7, score = 400 // 57 | mov dword ptr [ebp - 0x130], eax // ff15???????? | // 6804010000 | mov dword ptr [ebp - 0x120], 0 // 6a00 | mov dword ptr [ebp - 0x124], ecx // 57 | lea esi, [esi*8 + 0x23a070] // e8???????? | // 57 | cmp dword ptr [esi], ebx $sequence_8 = { 83c404 6a00 6a64 52 } // n = 4, score = 300 // 83c404 | test eax, eax // 6a00 | je 0x1c // 6a64 | dec eax // 52 | sub esp, 0x20 $sequence_9 = { 8a95e4feffff 88940df0feffff ebd0 c785e8feffff00000000 c785e0feffff00000000 eb0f } // n = 6, score = 200 // 8a95e4feffff | add ecx, dword ptr [ebp - 0x124] // 88940df0feffff | movsx edx, byte ptr [ecx] // ebd0 | movzx eax, byte ptr [ebp - 0x112] // c785e8feffff00000000 | xor edx, eax // c785e0feffff00000000 | mov ecx, dword ptr [ebp + 0x18] // eb0f | movsx edx, byte ptr [ecx] $sequence_10 = { 888deffeffff 0fb695e8feffff 8b85e0feffff 8a8c15f0feffff } // n = 4, score = 200 // 888deffeffff | xor eax, ebp // 0fb695e8feffff | mov dword ptr [ebp - 0xc], eax // 8b85e0feffff | mov dword ptr [ebp - 8], 0 // 8a8c15f0feffff | mov ecx, dword ptr [ebp + 0x10] $sequence_11 = { 408832 4181f900010000 7c9a 488bdd 85ed } // n = 5, score = 200 // 408832 | mov al, byte ptr [ebp - 0x111] // 4181f900010000 | mov byte ptr [ebp + edx - 0x110], al // 7c9a | mov dword ptr [ebp - 0x124], 0 // 488bdd | jmp 0x28 // 85ed | mov byte ptr [ebp - 0x111], cl $sequence_12 = { 0fb695e8feffff 8a85effeffff 888415f0feffff e9???????? c785dcfeffff00000000 eb0f } // n = 6, score = 200 // 0fb695e8feffff | push edx // 8a85effeffff | push eax // 888415f0feffff | push ebp // e9???????? | // c785dcfeffff00000000 | mov ebp, esp // eb0f | sub esp, 0x124 $sequence_13 = { 55 8bec 81ec24010000 a1???????? 33c5 8945f4 c745f800000000 } // n = 7, score = 200 // 55 | push 0 // 8bec | push 0x64 // 81ec24010000 | push edx // a1???????? | // 33c5 | push eax // 8945f4 | add esp, 4 // c745f800000000 | push 0 $sequence_14 = { 4c03c0 410fb6c2 450fb608 4803d0 0fb602 } // n = 5, score = 200 // 4c03c0 | mov byte ptr [ebp + ecx - 0x110], dl // 410fb6c2 | jmp 0xffffffd9 // 450fb608 | mov dword ptr [ebp - 0x118], 0 // 4803d0 | mov dword ptr [ebp - 0x120], 0 // 0fb602 | jmp 0x2e $sequence_15 = { 81bde0feffff00010000 0f8d84000000 8b8de0feffff 0fb68c0df0feffff } // n = 4, score = 200 // 81bde0feffff00010000 | inc esi // 0f8d84000000 | mov al, byte ptr [ecx] // 8b8de0feffff | mov byte ptr [ebp + esi - 0x105], al // 0fb68c0df0feffff | mov byte ptr [ecx], dl $sequence_16 = { 7d0d 41ffca 4181ca00ffffff 41ffc2 0fb6c1 4c8d0424 488d1424 } // n = 7, score = 200 // 7d0d | movzx eax, byte ptr [ebp - 8] // 41ffca | mov cl, byte ptr [ebp + eax - 0x110] // 4181ca00ffffff | mov byte ptr [ebp - 0x111], cl // 41ffc2 | movzx edx, byte ptr [ebp - 4] // 0fb6c1 | movzx eax, byte ptr [ebp - 8] // 4c8d0424 | mov cl, byte ptr [ebp + edx - 0x110] // 488d1424 | movzx edx, byte ptr [ebp - 0x118] $sequence_17 = { 488d1424 448bd1 8bc1 0f1f840000000000 8802 ffc0 488d5201 } // n = 7, score = 200 // 488d1424 | mov byte ptr [edx], dh // 448bd1 | inc ecx // 8bc1 | cmp ecx, 0x100 // 0f1f840000000000 | jl 0xffffff9c // 8802 | dec eax // ffc0 | mov ebx, ebp // 488d5201 | test ebp, ebp $sequence_18 = { 8b4d10 038ddcfeffff 0fbe11 0fb685eefeffff 33d0 8b4d18 } // n = 6, score = 200 // 8b4d10 | push 0x64 // 038ddcfeffff | add esp, 4 // 0fbe11 | push 0 // 0fb685eefeffff | push 0x64 // 33d0 | push edx // 8b4d18 | add esp, 4 $sequence_19 = { 4833c4 4889842400010000 4c8b9c2440010000 33c9 } // n = 4, score = 200 // 4833c4 | movzx edx, byte ptr [ebp - 0x118] // 4889842400010000 | mov eax, dword ptr [ebp - 0x120] // 4c8b9c2440010000 | mov cl, byte ptr [ebp + edx - 0x110] // 33c9 | mov dl, byte ptr [ebp - 0x11c] $sequence_20 = { 48897c2420 4156 4881ec10010000 488b05???????? 4833c4 } // n = 5, score = 200 // 48897c2420 | dec eax // 4156 | xor eax, esp // 4881ec10010000 | dec eax // 488b05???????? | // 4833c4 | mov dword ptr [esp + 0x100], eax $sequence_21 = { 7908 49 81c900ffffff 41 898de8feffff 8b85e0feffff 8a8c05f0feffff } // n = 7, score = 200 // 7908 | add esp, 0x28 // 49 | push ebx // 81c900ffffff | push esi // 41 | add esp, 0x28 // 898de8feffff | lea eax, [esi + 1] // 8b85e0feffff | nop // 8a8c05f0feffff | mov cl, byte ptr [esi] $sequence_22 = { 41ffc1 4803d0 48ffc3 0fb602 } // n = 4, score = 200 // 41ffc1 | mov byte ptr [ebp + edx - 0x110], al // 4803d0 | movzx ecx, byte ptr [ebp - 8] // 48ffc3 | movzx edx, byte ptr [ebp + ecx - 0x110] // 0fb602 | movzx eax, byte ptr [ebp - 4] $sequence_23 = { ffc0 488d5201 3d00010000 7cf1 448bc1 448bc9 488d1c24 } // n = 7, score = 200 // ffc0 | movzx ecx, byte ptr [ebp + eax - 0x110] // 488d5201 | jge 0xf // 3d00010000 | inc ecx // 7cf1 | dec edx // 448bc1 | inc ecx // 448bc9 | or edx, 0xffffff00 // 488d1c24 | inc ecx $sequence_24 = { 8955fc 0fb645f8 8a8c05f0feffff 888deffeffff 0fb655fc 0fb645f8 8a8c15f0feffff } // n = 7, score = 200 // 8955fc | push 0 // 0fb645f8 | push 0x64 // 8a8c05f0feffff | push edx // 888deffeffff | push eax // 0fb655fc | add esp, 4 // 0fb645f8 | push 0 // 8a8c15f0feffff | push 0x64 $sequence_25 = { 8810 33ff 8d5001 8b048d606d4100 47 4e 807d1300 } // n = 7, score = 100 // 8810 | push 0x104 // 33ff | push 0x104 // 8d5001 | mov edi, eax // 8b048d606d4100 | push 0 // 47 | push edi // 4e | push 0x104 // 807d1300 | push 0x104 $sequence_26 = { ff95dcfeffff 8985ecfeffff 6800800000 6804010000 8b85d8feffff 50 } // n = 6, score = 100 // ff95dcfeffff | inc ecx // 8985ecfeffff | dec eax // 6800800000 | add edx, eax // 6804010000 | dec eax // 8b85d8feffff | inc ebx // 50 | movzx eax, byte ptr [edx] $sequence_27 = { d85223 000453 2300 285323 0023 d18a0688078a 46 } // n = 7, score = 100 // d85223 | inc eax // 000453 | dec eax // 2300 | lea edx, [edx + 1] // 285323 | dec eax // 0023 | mov dword ptr [esp + 0x20], edi // d18a0688078a | inc ecx // 46 | push esi $sequence_28 = { 33f6 488d1de8a30000 8d7e24 837b0801 7522 4863c6 } // n = 6, score = 100 // 33f6 | mov ecx, edi // 488d1de8a30000 | je 0x2c2 // 8d7e24 | dec eax // 837b0801 | lea eax, [0xac9b] // 7522 | dec edx // 4863c6 | mov eax, dword ptr [eax + ebp*8] $sequence_29 = { 68???????? ff15???????? 8b3d???????? 85c0 0f84e4000000 6a39 } // n = 6, score = 100 // 68???????? | // ff15???????? | // 8b3d???????? | // 85c0 | push 0 // 0f84e4000000 | push 0 // 6a39 | push 3 $sequence_30 = { 8d8ddcfeffff 8d5101 8a01 41 } // n = 4, score = 100 // 8d8ddcfeffff | mov edi, eax // 8d5101 | push 0 // 8a01 | push 0x104 // 41 | push 0x104 $sequence_31 = { 488d05c3910000 483bc8 7405 e8???????? bf0d000000 8bcf } // n = 6, score = 100 // 488d05c3910000 | mov ecx, 3 // 483bc8 | dec eax // 7405 | mov eax, ecx // e8???????? | // bf0d000000 | dec ecx // 8bcf | sub eax, esi $sequence_32 = { 0f84bc020000 488d059bac0000 4a8b04e8 41f644040880 0f84a5020000 } // n = 5, score = 100 // 0f84bc020000 | dec eax // 488d059bac0000 | sar eax, 1 // 4a8b04e8 | dec eax // 41f644040880 | lea eax, [0x91c3] // 0f84a5020000 | dec eax $sequence_33 = { c745e4a06c4100 a1???????? 33db 43 895de0 } // n = 5, score = 100 // c745e4a06c4100 | mov edi, eax // a1???????? | // 33db | movzx eax, byte ptr [eax + edi] // 43 | movzx ecx, dl // 895de0 | add ebx, eax $sequence_34 = { 8b45e0 8b0485606d4100 f644180401 7428 57 e8???????? } // n = 6, score = 100 // 8b45e0 | add ebx, ecx // 8b0485606d4100 | and ebx, 0x800000ff // f644180401 | push 0 // 7428 | push 3 // 57 | push 0x50 // e8???????? | $sequence_35 = { 3d00010000 7d10 8a8c181d010000 8888b0a52300 40 ebe6 ff35???????? } // n = 7, score = 100 // 3d00010000 | inc eax // 7d10 | dec eax // 8a8c181d010000 | lea edx, [edx + 1] // 8888b0a52300 | cmp eax, 0x100 // 40 | jl 0xfffffff8 // ebe6 | inc esp // ff35???????? | $sequence_36 = { 59 8945e4 8b7508 c7465cd8812300 } // n = 4, score = 100 // 59 | mov eax, ecx // 8945e4 | inc esp // 8b7508 | mov ecx, ecx // c7465cd8812300 | dec eax $sequence_37 = { e8???????? 488d053bae0000 488903 488bc3 } // n = 4, score = 100 // e8???????? | // 488d053bae0000 | cmp ecx, eax // 488903 | je 7 // 488bc3 | mov edi, 0xd $sequence_38 = { 488d4dbc 4c8d0509980000 488d0c41 41b903000000 488bc1 492bc6 48d1f8 } // n = 7, score = 100 // 488d4dbc | dec eax // 4c8d0509980000 | lea ecx, [ebp - 0x44] // 488d0c41 | dec esp // 41b903000000 | lea eax, [0x9809] // 488bc1 | dec eax // 492bc6 | lea ecx, [ecx + eax*2] // 48d1f8 | inc ecx $sequence_39 = { 50 ff15???????? 8985d0feffff c785e0feffff00000000 8b0d???????? 898ddcfeffff } // n = 6, score = 100 // 50 | cmp eax, 0x100 // ff15???????? | // 8985d0feffff | jl 0xfffffff8 // c785e0feffff00000000 | inc ecx // 8b0d???????? | // 898ddcfeffff | movzx eax, al $sequence_40 = { 0f8463010000 488d2d05f00000 41bf14030000 4c8d0518980000 } // n = 4, score = 100 // 0f8463010000 | inc ecx // 488d2d05f00000 | test byte ptr [esp + eax + 8], 0x80 // 41bf14030000 | je 0x2b5 // 4c8d0518980000 | dec eax $sequence_41 = { 7d10 668b4c4310 66890c4590b22300 40 } // n = 4, score = 100 // 7d10 | mov edx, ecx // 668b4c4310 | mov eax, ecx // 66890c4590b22300 | nop dword ptr [eax + eax] // 40 | mov byte ptr [edx], al $sequence_42 = { 8d34f570a02300 391e 7404 8bc7 eb6e } // n = 5, score = 100 // 8d34f570a02300 | dec eax // 391e | lea edx, [esp] // 7404 | inc ecx // 8bc7 | inc ecx // eb6e | dec eax $sequence_43 = { 8b95e4feffff 52 ff15???????? 8985d8feffff 6a00 6804010000 8d85f0feffff } // n = 7, score = 100 // 8b95e4feffff | lea ebx, [esp] // 52 | dec esp // ff15???????? | // 8985d8feffff | lea eax, [esp] // 6a00 | dec eax // 6804010000 | lea edx, [esp] // 8d85f0feffff | dec esp $sequence_44 = { 72ed 48833d????????00 741f 488d0d4a140100 e8???????? 85c0 740f } // n = 7, score = 100 // 72ed | lea eax, [0xae3b] // 48833d????????00 | // 741f | dec eax // 488d0d4a140100 | mov dword ptr [ebx], eax // e8???????? | // 85c0 | dec eax // 740f | mov eax, ebx $sequence_45 = { 4883ec20 4883610800 488d05529c0000 c6411000 } // n = 4, score = 100 // 4883ec20 | xor esi, esi // 4883610800 | dec eax // 488d05529c0000 | lea ebx, [0xa3e8] // c6411000 | lea edi, [esi + 0x24] condition: 7 of them and filesize < 262144 }