SYMBOLCOMMON_NAMEaka. SYNONYMS
win.gacrux (Back to overview)

Gacrux


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References
2020-10-24KrabsOnSecurityMr. Krabs
@online{krabs:20201024:gacrux:a82613c, author = {Mr. Krabs}, title = {{Gacrux – a basic C malware with a custom PE loader}}, date = {2020-10-24}, organization = {KrabsOnSecurity}, url = {https://krabsonsecurity.com/2020/10/24/gacrux-a-basic-c-malware-with-a-custom-pe-loader/}, language = {English}, urldate = {2020-10-29} } Gacrux – a basic C malware with a custom PE loader
Gacrux
Yara Rules
[TLP:WHITE] win_gacrux_auto (20220411 | Detects win.gacrux.)
rule win_gacrux_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2022-04-08"
        version = "1"
        description = "Detects win.gacrux."
        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.gacrux"
        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 = { 4c 3bd0 7419 ffc1 41 3bc8 }
            // n = 6, score = 300
            //   4c                   | dec                 esp
            //   3bd0                 | cmp                 edx, eax
            //   7419                 | je                  0x1b
            //   ffc1                 | inc                 ecx
            //   41                   | inc                 ecx
            //   3bc8                 | cmp                 ecx, eax

        $sequence_1 = { f6c308 0f84cc000000 41 81482108020000 41 0fb701 49 }
            // n = 7, score = 300
            //   f6c308               | test                bl, 8
            //   0f84cc000000         | je                  0xd2
            //   41                   | inc                 ecx
            //   81482108020000       | or                  dword ptr [eax + 0x21], 0x208
            //   41                   | inc                 ecx
            //   0fb701               | movzx               eax, word ptr [ecx]
            //   49                   | dec                 ecx

        $sequence_2 = { 8bcd 44 0fb6d2 41 c1e217 84d2 45 }
            // n = 7, score = 300
            //   8bcd                 | mov                 ecx, ebp
            //   44                   | inc                 esp
            //   0fb6d2               | movzx               edx, dl
            //   41                   | inc                 ecx
            //   c1e217               | shl                 edx, 0x17
            //   84d2                 | test                dl, dl
            //   45                   | inc                 ebp

        $sequence_3 = { 83f8ff 7404 a810 7403 40 32ff }
            // n = 6, score = 300
            //   83f8ff               | cmp                 eax, -1
            //   7404                 | je                  6
            //   a810                 | test                al, 0x10
            //   7403                 | je                  5
            //   40                   | inc                 eax
            //   32ff                 | xor                 bh, bh

        $sequence_4 = { 7423 48 8b12 49 }
            // n = 4, score = 300
            //   7423                 | je                  0x25
            //   48                   | dec                 eax
            //   8b12                 | mov                 edx, dword ptr [edx]
            //   49                   | dec                 ecx

        $sequence_5 = { 4d 8bd7 41 80fc05 7216 be01000000 4c }
            // n = 7, score = 300
            //   4d                   | dec                 ebp
            //   8bd7                 | mov                 edx, edi
            //   41                   | inc                 ecx
            //   80fc05               | cmp                 ah, 5
            //   7216                 | jb                  0x18
            //   be01000000           | mov                 esi, 1
            //   4c                   | dec                 esp

        $sequence_6 = { 48 8dac24f0feffff 48 81ec10020000 6548 8b0425???????? 8bd9 }
            // n = 7, score = 300
            //   48                   | dec                 eax
            //   8dac24f0feffff       | lea                 ebp, dword ptr [esp - 0x110]
            //   48                   | dec                 eax
            //   81ec10020000         | sub                 esp, 0x210
            //   6548                 | dec                 eax
            //   8b0425????????       |                     
            //   8bd9                 | mov                 ebx, ecx

        $sequence_7 = { 8bc2 41 8bd2 48 85c9 7415 }
            // n = 6, score = 300
            //   8bc2                 | mov                 eax, edx
            //   41                   | inc                 ecx
            //   8bd2                 | mov                 edx, edx
            //   48                   | dec                 eax
            //   85c9                 | test                ecx, ecx
            //   7415                 | je                  0x17

        $sequence_8 = { 0f85d7000000 8a453a 3c01 7574 8b442424 83f805 7524 }
            // n = 7, score = 300
            //   0f85d7000000         | jne                 0xdd
            //   8a453a               | mov                 al, byte ptr [ebp + 0x3a]
            //   3c01                 | cmp                 al, 1
            //   7574                 | jne                 0x76
            //   8b442424             | mov                 eax, dword ptr [esp + 0x24]
            //   83f805               | cmp                 eax, 5
            //   7524                 | jne                 0x26

        $sequence_9 = { 895c2410 48 89742418 57 48 81ec20040000 }
            // n = 6, score = 300
            //   895c2410             | mov                 dword ptr [esp + 0x10], ebx
            //   48                   | dec                 eax
            //   89742418             | mov                 dword ptr [esp + 0x18], esi
            //   57                   | push                edi
            //   48                   | dec                 eax
            //   81ec20040000         | sub                 esp, 0x420

    condition:
        7 of them and filesize < 122880
}
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