SYMBOLCOMMON_NAMEaka. SYNONYMS
win.kutaki (Back to overview)

Kutaki

URLhaus    

Cofense characterizes Kutaki as a data stealer that uses old-school techniques to detect sandboxes and debugging. Kutaki however works quite well against unhardened virtual machines and other analysis devices. By backdooring a legitimate application, it can fool unsophisticated detection methodologies.

References
2019-01-21CofenseCofense
@online{cofense:20190121:kutaki:3bff835, author = {Cofense}, title = {{The Kutaki Malware Bypasses Gateways to Steal Users’ Credentials}}, date = {2019-01-21}, organization = {Cofense}, url = {https://cofense.com/kutaki-malware-bypasses-gateways-steal-users-credentials/}, language = {English}, urldate = {2020-01-06} } The Kutaki Malware Bypasses Gateways to Steal Users’ Credentials
Kutaki
Yara Rules
[TLP:WHITE] win_kutaki_auto (20230407 | Detects win.kutaki.)
rule win_kutaki_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2023-03-28"
        version = "1"
        description = "Detects win.kutaki."
        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.kutaki"
        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 = { ff15???????? 8d55c0 52 8d45dc 50 }
            // n = 5, score = 700
            //   ff15????????         |                     
            //   8d55c0               | lea                 edx, [ebp - 0x40]
            //   52                   | push                edx
            //   8d45dc               | lea                 eax, [ebp - 0x24]
            //   50                   | push                eax

        $sequence_1 = { 8b9558ffffff 52 8b8554ffffff 50 ff15???????? 898510ffffff eb0a }
            // n = 7, score = 700
            //   8b9558ffffff         | mov                 edx, dword ptr [ebp - 0xa8]
            //   52                   | push                edx
            //   8b8554ffffff         | mov                 eax, dword ptr [ebp - 0xac]
            //   50                   | push                eax
            //   ff15????????         |                     
            //   898510ffffff         | mov                 dword ptr [ebp - 0xf0], eax
            //   eb0a                 | jmp                 0xc

        $sequence_2 = { 8bf0 ffd7 a1???????? 6685f6 0f8d23010000 }
            // n = 5, score = 700
            //   8bf0                 | mov                 esi, eax
            //   ffd7                 | call                edi
            //   a1????????           |                     
            //   6685f6               | test                si, si
            //   0f8d23010000         | jge                 0x129

        $sequence_3 = { ff5244 dbe2 898504ffffff 83bd04ffffff00 7d23 6a44 }
            // n = 6, score = 700
            //   ff5244               | call                dword ptr [edx + 0x44]
            //   dbe2                 | fnclex              
            //   898504ffffff         | mov                 dword ptr [ebp - 0xfc], eax
            //   83bd04ffffff00       | cmp                 dword ptr [ebp - 0xfc], 0
            //   7d23                 | jge                 0x25
            //   6a44                 | push                0x44

        $sequence_4 = { 83c201 0f8042020000 663945e8 8913 750a 663945e0 0f84bc010000 }
            // n = 7, score = 700
            //   83c201               | add                 edx, 1
            //   0f8042020000         | jo                  0x248
            //   663945e8             | cmp                 word ptr [ebp - 0x18], ax
            //   8913                 | mov                 dword ptr [ebx], edx
            //   750a                 | jne                 0xc
            //   663945e0             | cmp                 word ptr [ebp - 0x20], ax
            //   0f84bc010000         | je                  0x1c2

        $sequence_5 = { 8d55e8 52 50 8b08 8bf0 ff5150 85c0 }
            // n = 7, score = 700
            //   8d55e8               | lea                 edx, [ebp - 0x18]
            //   52                   | push                edx
            //   50                   | push                eax
            //   8b08                 | mov                 ecx, dword ptr [eax]
            //   8bf0                 | mov                 esi, eax
            //   ff5150               | call                dword ptr [ecx + 0x50]
            //   85c0                 | test                eax, eax

        $sequence_6 = { 8b4508 8b08 2b5114 899554ffffff 8b5508 8b02 8b8d54ffffff }
            // n = 7, score = 700
            //   8b4508               | mov                 eax, dword ptr [ebp + 8]
            //   8b08                 | mov                 ecx, dword ptr [eax]
            //   2b5114               | sub                 edx, dword ptr [ecx + 0x14]
            //   899554ffffff         | mov                 dword ptr [ebp - 0xac], edx
            //   8b5508               | mov                 edx, dword ptr [ebp + 8]
            //   8b02                 | mov                 eax, dword ptr [edx]
            //   8b8d54ffffff         | mov                 ecx, dword ptr [ebp - 0xac]

        $sequence_7 = { f7f9 6bc004 0f80f8070000 8945c4 c745fc0e000000 }
            // n = 5, score = 700
            //   f7f9                 | idiv                ecx
            //   6bc004               | imul                eax, eax, 4
            //   0f80f8070000         | jo                  0x7fe
            //   8945c4               | mov                 dword ptr [ebp - 0x3c], eax
            //   c745fc0e000000       | mov                 dword ptr [ebp - 4], 0xe

        $sequence_8 = { 50 6a02 8d8d78ffffff 51 }
            // n = 4, score = 700
            //   50                   | push                eax
            //   6a02                 | push                2
            //   8d8d78ffffff         | lea                 ecx, [ebp - 0x88]
            //   51                   | push                ecx

        $sequence_9 = { 50 ff92f8060000 8985b8feffff 83bdb8feffff00 7d23 68f8060000 68???????? }
            // n = 7, score = 700
            //   50                   | push                eax
            //   ff92f8060000         | call                dword ptr [edx + 0x6f8]
            //   8985b8feffff         | mov                 dword ptr [ebp - 0x148], eax
            //   83bdb8feffff00       | cmp                 dword ptr [ebp - 0x148], 0
            //   7d23                 | jge                 0x25
            //   68f8060000           | push                0x6f8
            //   68????????           |                     

    condition:
        7 of them and filesize < 1335296
}
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