rule win_crytox_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2026-05-04"
        version = "1"
        description = "Detects win.crytox."
        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.crytox"
        malpedia_rule_date = "20260422"
        malpedia_hash = "a182e35da64e6d71cb55f125c4d4225196523f14"
        malpedia_version = "20260504"
        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 = { e8???????? 8d5640 8d4320 896c2404 891424 89442408 8954241c }
            // n = 7, score = 100
            //   e8????????           |                     
            //   8d5640               | test                eax, eax
            //   8d4320               | je                  0x5a4
            //   896c2404             | mov                 dword ptr [esp], 0x664c3c
            //   891424               | lea                 eax, [ebx + 0x39]
            //   89442408             | mov                 dword ptr [esp + 0x10], 0x68
            //   8954241c             | mov                 dword ptr [esp + 8], ebp

        $sequence_1 = { f20f70daff 660ffde0 660ffdd8 660f67e4 660f67db 660f7e20 660f7e1c08 }
            // n = 7, score = 100
            //   f20f70daff           | lea                 esi, [ecx + eax*4]
            //   660ffde0             | jmp                 0x1bd
            //   660ffdd8             | mov                 eax, dword ptr [esp + 0x1104]
            //   660f67e4             | mov                 ebp, dword ptr [esp + 0xa8]
            //   660f67db             | mov                 ecx, dword ptr [esp + 0x78]
            //   660f7e20             | mov                 eax, dword ptr [eax + 8]
            //   660f7e1c08           | cmp                 eax, dword ptr [esp + 0x70]

        $sequence_2 = { df0448 d8cd dec1 df0450 8b9424d4000000 d8cb dec1 }
            // n = 7, score = 100
            //   df0448               | mov                 word ptr [esp + 0x24], ax
            //   d8cd                 | fdivp               st(1)
            //   dec1                 | fild                dword ptr [ebp + 0x1ce9c]
            //   df0450               | fnstcw              word ptr [esp + 0xa6]
            //   8b9424d4000000       | movzx               eax, word ptr [esp + 0xa6]
            //   d8cb                 | mov                 ah, 0xc
            //   dec1                 | mov                 word ptr [esp + 0xa4], ax

        $sequence_3 = { e8???????? 8d742600 ff15???????? bfffffffff c70016000000 ebca ff15???????? }
            // n = 7, score = 100
            //   e8????????           |                     
            //   8d742600             | mov                 dword ptr [ebp - 0x44], eax
            //   ff15????????         |                     
            //   bfffffffff           | lea                 eax, [eax + eax - 1]
            //   c70016000000         | imul                ax, word ptr [ebp]
            //   ebca                 | mov                 word ptr [ebp], ax
            //   ff15????????         |                     

        $sequence_4 = { dddc ddd8 ddd8 ddd8 d9c9 db7c2430 d91424 }
            // n = 7, score = 100
            //   dddc                 | fstp                qword ptr [esp + 0x28]
            //   ddd8                 | ja                  0x1ad
            //   ddd8                 | add                 ebx, dword ptr [esp + 0x30]
            //   ddd8                 | add                 edi, 2
            //   d9c9                 | cmp                 edi, dword ptr [esp + 0x40]
            //   db7c2430             | fstp                st(2)
            //   d91424               | fxch                st(1)

        $sequence_5 = { dec1 d95c247c e8???????? d9c0 d9fa dbe8 d944242c }
            // n = 7, score = 100
            //   dec1                 | faddp               st(1)
            //   d95c247c             | fld                 dword ptr [esp + 0x10]
            //   e8????????           |                     
            //   d9c0                 | fmul                st(2)
            //   d9fa                 | fmul                st(4)
            //   dbe8                 | faddp               st(1)
            //   d944242c             | fld                 dword ptr [esp + 0x14]

        $sequence_6 = { d835???????? b40c 6689442424 dec9 d96c2424 db5c2420 d96c2426 }
            // n = 7, score = 100
            //   d835????????         |                     
            //   b40c                 | faddp               st(3)
            //   6689442424           | fxch                st(2)
            //   dec9                 | fadd                st(3)
            //   d96c2424             | fst                 dword ptr [ebx + ecx*8]
            //   db5c2420             | fsubr               dword ptr [ecx + eax*4]
            //   d96c2426             | mov                 eax, ebx

        $sequence_7 = { e8???????? 8b4310 8b6b0c 83f807 89442418 89c7 0f8efe000000 }
            // n = 7, score = 100
            //   e8????????           |                     
            //   8b4310               | mov                 dword ptr [esp], eax
            //   8b6b0c               | mov                 eax, edi
            //   83f807               | xor                 edx, edx
            //   89442418             | xor                 ecx, ecx
            //   89c7                 | mov                 esi, dword ptr [ebx + 0xc]
            //   0f8efe000000         | mov                 edi, dword ptr [esp + 0x38]

        $sequence_8 = { e8???????? 85c0 0f8583010000 e8???????? 83f804 7e14 c7442404b0966600 }
            // n = 7, score = 100
            //   e8????????           |                     
            //   85c0                 | test                eax, eax
            //   0f8583010000         | je                  0x191
            //   e8????????           |                     
            //   83f804               | mov                 dword ptr [esp], ebx
            //   7e14                 | mov                 edi, eax
            //   c7442404b0966600     | test                eax, eax

        $sequence_9 = { e8???????? d99c9e98000000 83c301 83fb04 75c6 d94704 30db }
            // n = 7, score = 100
            //   e8????????           |                     
            //   d99c9e98000000       | fstp                dword ptr [esp + 0xac]
            //   83c301               | fld                 dword ptr [esp + 0xac]
            //   83fb04               | fmulp               st(1)
            //   75c6                 | fdivr               dword ptr [esp + 0x2c]
            //   d94704               | mov                 eax, dword ptr [esp + 0x4c]
            //   30db                 | fld1                

    condition:
        7 of them and filesize < 6156288
}

import "pe"
rule win_crytox_w0 {
  meta:
    description = "Detect variants of Crytox Ransomware"
    author = "Jake Goldi"
    date = "2022-09-29"
    packed_hash1 = "32eef267a1192a9a739ccaaae0266bc66707bb64768a764541ecb039a50cba67"
    hash2 = "11ea0d7e0ebe15b8147d39e72773221d11c2cf84e2d8d6164102c65e797eef6d"
    hash3 = "68fae79a2eca125090bd2a8badc46ed4324c38f2ff24db702d09c3d7687e0047"
    hash4 = "a0a6c2937b6a8b2bc1214ace8255adc6992b553b9e740c3fe1543e089e8437aa"
    source = "https://raw.githubusercontent.com/taogoldi/YARA/main/ransomware/crytox_ransom.yara"
    
    version="1.0"
    phase = "experimental"
    url = "https://www.zscaler.com/blogs/security-research/technical-analysis-crytox-ransomware"
    malware = "Win64.Ransom.Crytox"
    
    malpedia_reference = "https://malpedia.caad.fkie.fraunhofer.de/details/win.crytox"
    malpedia_rule_date = "20220930"
    malpedia_hash = ""
    malpedia_version = "20220930"
    malpedia_license = "CC BY-SA 4.0"
    malpedia_sharing = "TLP:WHITE"
    
    
  strings:
    $s1 = "utox" wide ascii nocase
    /*
        hash 2: 11ea0d7e0ebe15b8147d39e72773221d11c2cf84e2d8d6164102c65e797eef6d

        FF 15 C9 22 00 00                       call    cs:GlobalAlloc
        48 89 85 58 FF FF FF                    mov     [rbp+hMem], rax ; unk_5F2520
        4C 8B E0                                mov     r12, rax
        
        48 8B C8                                mov     rcx, rax

        E8 DD 13 00 00                          call    sub_1402E940E
        48 C7 C1 C0 01 00 00                    mov     rcx, 448
        49 8D 94 24 08 04 00 00                 lea     rdx, [r12+408h]

        4C 8D 05 29 20 00 00                    lea     r8, unk_1402EA070
 
        4C 8D 8D A4 FD FF FF                    lea     r9, [rbp+var_25C]
        E8 A2 11 00 00                          call    sub_1402E91F5
        48 8B 8D 58 FF FF FF                    mov     rcx, [rbp+hMem] ; hMem
        FF 15 90 22 00 00                       call    cs:GlobalFree 

        -------------   

        hash 3: 68fae79a2eca125090bd2a8badc46ed4324c38f2ff24db702d09c3d7687e0047

        FF 15 C9 22 00 00                       call    cs:GlobalAlloc
        48 89 85 58 FF FF FF                    mov     [rbp+hMem], rax
        4C 8B E0                                mov     r12, rax
        
        90                                      nop
        50                                      push    rax
        59                                      pop     rcx
        
        E8 E2 13 00 00                          call    sub_1402E9413
        48 C7 C1 C0 01 00 00                    mov     rcx, 1C0h
        49 8D 94 24 08 04 00 00                 lea     rdx, [r12+408h]

        4C 8D 05 29 20 00 00                    lea     r8, unk_1402EA070
        
        4C 8D 8D A4 FD FF FF                    lea     r9, [rbp+var_25C]
        E8 A7 11 00 00                          call    sub_1402E91FA
        48 8B 8D 58 FF FF FF                    mov     rcx, [rbp+hMem] ; hMem
        FF 15 90 22 00 00                       call    cs:GlobalFree

        ------------- 

        hash 4: a0a6c2937b6a8b2bc1214ace8255adc6992b553b9e740c3fe1543e089e8437aa

        FF 15 C9 22 00 00                       call    cs:GlobalAlloc
        48 89 85 58 FF FF FF                    mov     [rbp+hMem], rax
        4C 8B E0                                mov     r12, rax
        48 8B C8                                mov     rcx, rax
        E8 61 12 00 00                          call    sub_1402E9292
        48 C7 C1 C0 01 00 00                    mov     rcx, 1C0h
        49 8D 94 24 08 04 00 00                 lea     rdx, [r12+408h]
        4C 8D 05 29 20 00 00                    lea     r8, unk_1402EA070
        4C 8D 8D A4 FD FF FF                    lea     r9, [rbp+var_25C]
        E8 26 10 00 00                          call    sub_1402E9079
        48 8B 8D 58 FF FF FF                    mov     rcx, [rbp+hMem] ; hMem
        FF 15 90 22 00 00                       call    cs:GlobalFre



    */

    $op1 = { FF 15 C9 22 00 00 48 89 85 58 FF FF FF 4C 8B E0 } 
    $op2 = { E8 ?? ?? 00 00 48 C7 C1 C0 01 00 00 49 8D 94 24 08 04 00 00 }
    $op3 = { 4C 8D 05 29 20 00 00 }
    $op4 = { 4C 8D 8D A4 FD FF FF E8 ?? 1? 00 00 48 8B 8D 58 FF FF FF FF 15 90 22 00 00 }

condition:
    uint16(0) == 0x5a4d and filesize < 5000KB and ((all of ($s*)) and (all of ($op*)))

}