SYMBOLCOMMON_NAMEaka. SYNONYMS
win.kaolin_rat (Back to overview)

Kaolin RAT

aka: KaolinTea

Actor(s): Lazarus Group

VTCollection    

Kaolin RAT is a complex modular RAT, with Release_TMain_x64.dll as its internal DLL name.

The malware provides standard backdoor functionality, including manipulation and listing of files and processes, exchanging the configuration, collecting the victim’s system info, opening a TCP connection, and executing local commands and collecting their outputs.

Also, it is designed to execute additional DLL payloads in memory via specific exported functions:
- _DoMyFunc,
- _DoMyFunc2,
- _DoMyThread,
- _DoMyCommandWork.

Functionally, Kaolin RAT relies on an accompanying trojanized curl library to handle network and exfiltration operations, by importing functions such as:
- SendDataFromURL,
- ZipFolder,
- UnzipStr,
- curl wrappers.

For C&C communication, it employs AES encryption and attempts to evade network detection by randomly selecting words from a hardcoded custom dictionary to populate POST request parameters. The malware's name is derived from one of these dictionary words ("kaolin").

The Kaolin RAT has been observed in Lazarus campaigns as a late-stage payload — typically following loaders like RollFling, RollSling, and RollMid — and serves also as a delivery vector for the FudModule rootkit with a 0-day exploit.

References
2024-04-18 ⋅ Avast ⋅ Luigino Camastra
From BYOVD to a 0-day: Unveiling Advanced Exploits in Cyber Recruiting Scams
FudModule Kaolin RAT
Yara Rules
[TLP:WHITE] win_kaolin_rat_auto (20260917 | Detects win.kaolin_rat.)
rule win_kaolin_rat_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2026-09-17"
        version = "1"
        description = "Detects win.kaolin_rat."
        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.kaolin_rat"
        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 = { 488b4230 488988f8000000 488d0ddb530300 488b4230 48898800010000 488d0dd1530300 488b4230 }
            // n = 7, score = 100
            //   488b4230             | dec                 eax
            //   488988f8000000       | lea                 ecx, [0x3579d]
            //   488d0ddb530300       | dec                 eax
            //   488b4230             | mov                 eax, dword ptr [edx + 0x20]
            //   48898800010000       | dec                 eax
            //   488d0dd1530300       | mov                 dword ptr [eax + 0xd0], ecx
            //   488b4230             | dec                 eax

        $sequence_1 = { 742f 0f1f4000 8b16 4903d7 498bc8 e8???????? 85c0 }
            // n = 7, score = 100
            //   742f                 | mov                 dword ptr [ebx - 0x60], 0xa
            //   0f1f4000             | dec                 ebp
            //   8b16                 | mov                 dword ptr [ebx - 0x78], eax
            //   4903d7               | dec                 ebp
            //   498bc8               | mov                 dword ptr [ebx - 0x70], ecx
            //   e8????????           |                     
            //   85c0                 | inc                 ebp

        $sequence_2 = { 488988d8000000 488d0dc6550300 488b4228 488988e0000000 488d0dbc550300 488b4228 488988e8000000 }
            // n = 7, score = 100
            //   488988d8000000       | mov                 dword ptr [ebx + 0x10], ebp
            //   488d0dc6550300       | dec                 eax
            //   488b4228             | mov                 dword ptr [ebx + 0x18], 0xf
            //   488988e0000000       | mov                 byte ptr [ebx], 0
            //   488d0dbc550300       | dec                 ecx
            //   488b4228             | mov                 eax, esi
            //   488988e8000000       | dec                 eax

        $sequence_3 = { 4889842418010000 488d842408010000 4883fa10 480f43842408010000 46880c30 42c644300100 eb0d }
            // n = 7, score = 100
            //   4889842418010000     | dec                 eax
            //   488d842408010000     | mov                 dword ptr [esp + 0x48], ecx
            //   4883fa10             | mov                 byte ptr [esp + 0x38], cl
            //   480f43842408010000     | mov    esi, ebp
            //   46880c30             | dec                 eax
            //   42c644300100         | cmp                 dword ptr [ebx + 0x10], ebp
            //   eb0d                 | jbe                 0x508

        $sequence_4 = { c1e102 2bc1 4863c8 420fb6442102 324302 41884305 8bc6 }
            // n = 7, score = 100
            //   c1e102               | mov                 byte ptr [ebx], 0xd
            //   2bc1                 | dec                 eax
            //   4863c8               | inc                 ebx
            //   420fb6442102         | add                 cl, 0x30
            //   324302               | inc                 ecx
            //   41884305             | mov                 byte ptr [ecx], cl
            //   8bc6                 | mov                 ecx, edx

        $sequence_5 = { e8???????? 4c8bcf 48833d????????10 4c0f430d???????? 48c7c7ffffffff 0f1f8000000000 }
            // n = 6, score = 100
            //   e8????????           |                     
            //   4c8bcf               | jmp                 0x9a7
            //   48833d????????10     |                     
            //   4c0f430d????????     |                     
            //   48c7c7ffffffff       | dec                 eax
            //   0f1f8000000000       | lea                 ecx, [ebp + 0x10]

        $sequence_6 = { 498bd7 498bcb ff15???????? 85c0 0f8409010000 448b13 4c8bdd }
            // n = 7, score = 100
            //   498bd7               | cmovae              esi, edi
            //   498bcb               | dec                 ecx
            //   ff15????????         |                     
            //   85c0                 | cmp                 esi, 0x10
            //   0f8409010000         | jae                 0x261
            //   448b13               | movups              xmm0, xmmword ptr [esi]
            //   4c8bdd               | movups              xmmword ptr [esp + 0x30], xmm0

        $sequence_7 = { 410f1106 0f104c2470 410f114e10 4c89642470 48c74424780f000000 c644246000 }
            // n = 6, score = 100
            //   410f1106             | dec                 esp
            //   0f104c2470           | mov                 edi, dword ptr [esp + 0xe8]
            //   410f114e10           | dec                 eax
            //   4c89642470           | mov                 edi, dword ptr [esp + 0x100]
            //   48c74424780f000000     | dec    eax
            //   c644246000           | cmp                 edi, 0x10

        $sequence_8 = { 41b800300000 4c89b424b0000000 488bd7 ff15???????? 4889442420 4c8bf0 }
            // n = 6, score = 100
            //   41b800300000         | lea                 eax, [ebp + 1]
            //   4c89b424b0000000     | xor                 ecx, ecx
            //   488bd7               | mov                 dword ptr [esp + 0x24c], 0
            //   ff15????????         |                     
            //   4889442420           | mov                 ebx, eax
            //   4c8bf0               | cmp                 eax, -1

        $sequence_9 = { 49c1fa06 4e8d1ced00000000 4d03dd 418a0438 41ffc1 4b8b8cd7f0070400 }
            // n = 6, score = 100
            //   49c1fa06             | dec                 eax
            //   4e8d1ced00000000     | mov                 dword ptr [ebx + 0x98], 0xf
            //   4d03dd               | dec                 eax
            //   418a0438             | mov                 dword ptr [ebx + 0x90], edi
            //   41ffc1               | inc                 eax
            //   4b8b8cd7f0070400     | mov                 byte ptr [ebx + 0x80], bh

    condition:
        7 of them and filesize < 581632
}
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