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 (20230407 | Detects win.gacrux.)
rule win_gacrux_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2023-03-28"
        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 = "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 = { 32f6 4c 8be9 4c }
            // n = 4, score = 300
            //   32f6                 | xor                 dh, dh
            //   4c                   | dec                 esp
            //   8be9                 | mov                 ebp, ecx
            //   4c                   | dec                 esp

        $sequence_1 = { 8905???????? 8915???????? 890d???????? 48 893d???????? 4c }
            // n = 6, score = 300
            //   8905????????         |                     
            //   8915????????         |                     
            //   890d????????         |                     
            //   48                   | dec                 eax
            //   893d????????         |                     
            //   4c                   | dec                 esp

        $sequence_2 = { 48 03ca 849c013c010000 740b 41 81cb00300000 45 }
            // n = 7, score = 300
            //   48                   | dec                 eax
            //   03ca                 | add                 ecx, edx
            //   849c013c010000       | test                byte ptr [ecx + eax + 0x13c], bl
            //   740b                 | je                  0xd
            //   41                   | inc                 ecx
            //   81cb00300000         | or                  ebx, 0x3000
            //   45                   | inc                 ebp

        $sequence_3 = { e9???????? 8a4504 24c7 3c05 7550 49 }
            // n = 6, score = 300
            //   e9????????           |                     
            //   8a4504               | mov                 al, byte ptr [ebp + 4]
            //   24c7                 | and                 al, 0xc7
            //   3c05                 | cmp                 al, 5
            //   7550                 | jne                 0x52
            //   49                   | dec                 ecx

        $sequence_4 = { 85d2 7416 48 8b0d???????? 48 }
            // n = 5, score = 300
            //   85d2                 | test                edx, edx
            //   7416                 | je                  0x18
            //   48                   | dec                 eax
            //   8b0d????????         |                     
            //   48                   | dec                 eax

        $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 = { 72c9 48 8d4c2420 e8???????? 48 8b5c2440 8bc7 }
            // n = 7, score = 300
            //   72c9                 | jb                  0xffffffcb
            //   48                   | dec                 eax
            //   8d4c2420             | lea                 ecx, [esp + 0x20]
            //   e8????????           |                     
            //   48                   | dec                 eax
            //   8b5c2440             | mov                 ebx, dword ptr [esp + 0x40]
            //   8bc7                 | mov                 eax, edi

        $sequence_7 = { f7d0 48 8b742410 41 }
            // n = 4, score = 300
            //   f7d0                 | not                 eax
            //   48                   | dec                 eax
            //   8b742410             | mov                 esi, dword ptr [esp + 0x10]
            //   41                   | inc                 ecx

        $sequence_8 = { 41 216d00 eb1d b90f0000c0 894c2460 }
            // n = 5, score = 300
            //   41                   | inc                 ecx
            //   216d00               | and                 dword ptr [ebp], ebp
            //   eb1d                 | jmp                 0x1f
            //   b90f0000c0           | mov                 ecx, 0xc000000f
            //   894c2460             | mov                 dword ptr [esp + 0x60], ecx

        $sequence_9 = { 03c6 83e801 746f 83e801 7463 83e801 }
            // n = 6, score = 300
            //   03c6                 | add                 eax, esi
            //   83e801               | sub                 eax, 1
            //   746f                 | je                  0x71
            //   83e801               | sub                 eax, 1
            //   7463                 | je                  0x65
            //   83e801               | sub                 eax, 1

    condition:
        7 of them and filesize < 122880
}
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