SYMBOLCOMMON_NAMEaka. SYNONYMS
win.kutaki (Back to overview)

Kutaki

VTCollection     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
2023-04-10SequretekSequretek
Kutaki Stealer - Analysis
Kutaki
2019-01-21CofenseCofense
The Kutaki Malware Bypasses Gateways to Steal Users’ Credentials
Kutaki
Yara Rules
[TLP:WHITE] win_kutaki_auto (20260504 | Detects win.kutaki.)
rule win_kutaki_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2026-05-04"
        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 = "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 = { e9???????? c745fc0a000000 c745fc0b000000 8b450c 6bc004 0f8037080000 83c002 }
            // n = 7, score = 700
            //   e9????????           |                     
            //   c745fc0a000000       | mov                 dword ptr [ebp - 4], 0xa
            //   c745fc0b000000       | mov                 dword ptr [ebp - 4], 0xb
            //   8b450c               | mov                 eax, dword ptr [ebp + 0xc]
            //   6bc004               | imul                eax, eax, 4
            //   0f8037080000         | jo                  0x83d
            //   83c002               | add                 eax, 2

        $sequence_1 = { 83bd80feffff00 7d26 68a0000000 68???????? 8b9584feffff 52 8b8580feffff }
            // n = 7, score = 700
            //   83bd80feffff00       | cmp                 dword ptr [ebp - 0x180], 0
            //   7d26                 | jge                 0x28
            //   68a0000000           | push                0xa0
            //   68????????           |                     
            //   8b9584feffff         | mov                 edx, dword ptr [ebp - 0x17c]
            //   52                   | push                edx
            //   8b8580feffff         | mov                 eax, dword ptr [ebp - 0x180]

        $sequence_2 = { 8d4de0 ff15???????? 8b4d08 6a00 8b11 8955c4 ffd3 }
            // n = 7, score = 700
            //   8d4de0               | lea                 ecx, [ebp - 0x20]
            //   ff15????????         |                     
            //   8b4d08               | mov                 ecx, dword ptr [ebp + 8]
            //   6a00                 | push                0
            //   8b11                 | mov                 edx, dword ptr [ecx]
            //   8955c4               | mov                 dword ptr [ebp - 0x3c], edx
            //   ffd3                 | call                ebx

        $sequence_3 = { c7458c00000000 8b4d8c f7d9 66894db4 8d4ddc ff15???????? 8d4dd4 }
            // n = 7, score = 700
            //   c7458c00000000       | mov                 dword ptr [ebp - 0x74], 0
            //   8b4d8c               | mov                 ecx, dword ptr [ebp - 0x74]
            //   f7d9                 | neg                 ecx
            //   66894db4             | mov                 word ptr [ebp - 0x4c], cx
            //   8d4ddc               | lea                 ecx, [ebp - 0x24]
            //   ff15????????         |                     
            //   8d4dd4               | lea                 ecx, [ebp - 0x2c]

        $sequence_4 = { ff15???????? 898584fcffff eb0a c78584fcffff00000000 8b9574ffffff 899564fdffff c78574ffffff00000000 }
            // n = 7, score = 700
            //   ff15????????         |                     
            //   898584fcffff         | mov                 dword ptr [ebp - 0x37c], eax
            //   eb0a                 | jmp                 0xc
            //   c78584fcffff00000000     | mov    dword ptr [ebp - 0x37c], 0
            //   8b9574ffffff         | mov                 edx, dword ptr [ebp - 0x8c]
            //   899564fdffff         | mov                 dword ptr [ebp - 0x29c], edx
            //   c78574ffffff00000000     | mov    dword ptr [ebp - 0x8c], 0

        $sequence_5 = { 66833801 7543 8b4dac 8b55d8 2b5114 899554ffffff }
            // n = 6, score = 700
            //   66833801             | cmp                 word ptr [eax], 1
            //   7543                 | jne                 0x45
            //   8b4dac               | mov                 ecx, dword ptr [ebp - 0x54]
            //   8b55d8               | mov                 edx, dword ptr [ebp - 0x28]
            //   2b5114               | sub                 edx, dword ptr [ecx + 0x14]
            //   899554ffffff         | mov                 dword ptr [ebp - 0xac], edx

        $sequence_6 = { 8d9574ffffff 8d4da4 ff15???????? 8b4dc8 898d20ffffff c745c800000000 }
            // n = 6, score = 700
            //   8d9574ffffff         | lea                 edx, [ebp - 0x8c]
            //   8d4da4               | lea                 ecx, [ebp - 0x5c]
            //   ff15????????         |                     
            //   8b4dc8               | mov                 ecx, dword ptr [ebp - 0x38]
            //   898d20ffffff         | mov                 dword ptr [ebp - 0xe0], ecx
            //   c745c800000000       | mov                 dword ptr [ebp - 0x38], 0

        $sequence_7 = { 8d4598 52 50 6a03 ff15???????? 83c41c 68???????? }
            // n = 7, score = 700
            //   8d4598               | lea                 eax, [ebp - 0x68]
            //   52                   | push                edx
            //   50                   | push                eax
            //   6a03                 | push                3
            //   ff15????????         |                     
            //   83c41c               | add                 esp, 0x1c
            //   68????????           |                     

        $sequence_8 = { 51 ff15???????? 8d8d3cffffff ff15???????? c745fc0a000000 83bd68ffffff00 }
            // n = 6, score = 700
            //   51                   | push                ecx
            //   ff15????????         |                     
            //   8d8d3cffffff         | lea                 ecx, [ebp - 0xc4]
            //   ff15????????         |                     
            //   c745fc0a000000       | mov                 dword ptr [ebp - 4], 0xa
            //   83bd68ffffff00       | cmp                 dword ptr [ebp - 0x98], 0

        $sequence_9 = { e9???????? c745fc34000000 8d45ac 50 e8???????? 8bd0 8d4da8 }
            // n = 7, score = 700
            //   e9????????           |                     
            //   c745fc34000000       | mov                 dword ptr [ebp - 4], 0x34
            //   8d45ac               | lea                 eax, [ebp - 0x54]
            //   50                   | push                eax
            //   e8????????           |                     
            //   8bd0                 | mov                 edx, eax
            //   8d4da8               | lea                 ecx, [ebp - 0x58]

    condition:
        7 of them and filesize < 1335296
}
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