rule win_observer_stealer_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2026-09-17"
        version = "1"
        description = "Detects win.observer_stealer."
        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.observer_stealer"
        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 = { 890b be???????? 894b04 894b08 894b0c 894b10 894b14 }
            // n = 7, score = 100
            //   890b                 | mov                 dword ptr [ebx], ecx
            //   be????????           |                     
            //   894b04               | mov                 dword ptr [ebx + 4], ecx
            //   894b08               | mov                 dword ptr [ebx + 8], ecx
            //   894b0c               | mov                 dword ptr [ebx + 0xc], ecx
            //   894b10               | mov                 dword ptr [ebx + 0x10], ecx
            //   894b14               | mov                 dword ptr [ebx + 0x14], ecx

        $sequence_1 = { 5e c3 81ec00010000 53 8b9c2410010000 55 56 }
            // n = 7, score = 100
            //   5e                   | pop                 esi
            //   c3                   | ret                 
            //   81ec00010000         | sub                 esp, 0x100
            //   53                   | push                ebx
            //   8b9c2410010000       | mov                 ebx, dword ptr [esp + 0x110]
            //   55                   | push                ebp
            //   56                   | push                esi

        $sequence_2 = { 8bc1 c3 56 8bf1 833e00 7422 8b4608 }
            // n = 7, score = 100
            //   8bc1                 | mov                 eax, ecx
            //   c3                   | ret                 
            //   56                   | push                esi
            //   8bf1                 | mov                 esi, ecx
            //   833e00               | cmp                 dword ptr [esi], 0
            //   7422                 | je                  0x24
            //   8b4608               | mov                 eax, dword ptr [esi + 8]

        $sequence_3 = { 56 53 e8???????? 59 59 8b4c2434 5f }
            // n = 7, score = 100
            //   56                   | push                esi
            //   53                   | push                ebx
            //   e8????????           |                     
            //   59                   | pop                 ecx
            //   59                   | pop                 ecx
            //   8b4c2434             | mov                 ecx, dword ptr [esp + 0x34]
            //   5f                   | pop                 edi

        $sequence_4 = { b001 eb02 32c0 5e c20800 8b4c2408 56 }
            // n = 7, score = 100
            //   b001                 | mov                 al, 1
            //   eb02                 | jmp                 4
            //   32c0                 | xor                 al, al
            //   5e                   | pop                 esi
            //   c20800               | ret                 8
            //   8b4c2408             | mov                 ecx, dword ptr [esp + 8]
            //   56                   | push                esi

        $sequence_5 = { 8d0442 50 e8???????? 56 55 ff74242c e8???????? }
            // n = 7, score = 100
            //   8d0442               | lea                 eax, [edx + eax*2]
            //   50                   | push                eax
            //   e8????????           |                     
            //   56                   | push                esi
            //   55                   | push                ebp
            //   ff74242c             | push                dword ptr [esp + 0x2c]
            //   e8????????           |                     

        $sequence_6 = { e8???????? 8b4f04 8b37 394c2424 755b 3bf1 741f }
            // n = 7, score = 100
            //   e8????????           |                     
            //   8b4f04               | mov                 ecx, dword ptr [edi + 4]
            //   8b37                 | mov                 esi, dword ptr [edi]
            //   394c2424             | cmp                 dword ptr [esp + 0x24], ecx
            //   755b                 | jne                 0x5d
            //   3bf1                 | cmp                 esi, ecx
            //   741f                 | je                  0x21

        $sequence_7 = { 8b8c2484000000 2bc1 99 f7fb 83f801 7709 }
            // n = 6, score = 100
            //   8b8c2484000000       | mov                 ecx, dword ptr [esp + 0x84]
            //   2bc1                 | sub                 eax, ecx
            //   99                   | cdq                 
            //   f7fb                 | idiv                ebx
            //   83f801               | cmp                 eax, 1
            //   7709                 | ja                  0xb

        $sequence_8 = { 56 8bf1 57 8b4604 8d7e08 3906 }
            // n = 6, score = 100
            //   56                   | push                esi
            //   8bf1                 | mov                 esi, ecx
            //   57                   | push                edi
            //   8b4604               | mov                 eax, dword ptr [esi + 4]
            //   8d7e08               | lea                 edi, [esi + 8]
            //   3906                 | cmp                 dword ptr [esi], eax

        $sequence_9 = { 83ef01 75b7 8b7508 8b4604 3b4608 7413 51 }
            // n = 7, score = 100
            //   83ef01               | sub                 edi, 1
            //   75b7                 | jne                 0xffffffb9
            //   8b7508               | mov                 esi, dword ptr [ebp + 8]
            //   8b4604               | mov                 eax, dword ptr [esi + 4]
            //   3b4608               | cmp                 eax, dword ptr [esi + 8]
            //   7413                 | je                  0x15
            //   51                   | push                ecx

    condition:
        7 of them and filesize < 614400
}