SYMBOLCOMMON_NAMEaka. SYNONYMS
win.unidentified_088 (Back to overview)

Unidentified 088 (Nim Ransomware)


Ransomware written in Nim.

References
2021-10-14Medium walmartglobaltechJason Reaves
@online{reaves:20211014:investigation:29ef29c, author = {Jason Reaves}, title = {{Investigation into the state of NIM malware Part 2}}, date = {2021-10-14}, organization = {Medium walmartglobaltech}, url = {https://medium.com/walmartglobaltech/investigation-into-the-state-of-nim-malware-part-2-a28bffffa671}, language = {English}, urldate = {2021-12-15} } Investigation into the state of NIM malware Part 2
Cobalt Strike NimGrabber Nimrev Unidentified 088 (Nim Ransomware)
Yara Rules
[TLP:WHITE] win_unidentified_088_auto (20230407 | Detects win.unidentified_088.)
rule win_unidentified_088_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2023-03-28"
        version = "1"
        description = "Detects win.unidentified_088."
        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.unidentified_088"
        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 = { 8b430c 0f85bd000000 e9???????? 8b07 85c0 7ee8 8d50ff }
            // n = 7, score = 100
            //   8b430c               | mov                 eax, dword ptr [ebx + 0xc]
            //   0f85bd000000         | jne                 0xc3
            //   e9????????           |                     
            //   8b07                 | mov                 eax, dword ptr [edi]
            //   85c0                 | test                eax, eax
            //   7ee8                 | jle                 0xffffffea
            //   8d50ff               | lea                 edx, [eax - 1]

        $sequence_1 = { 8d4dd0 ba01000000 0fb63c38 8b45ac c1e710 e8???????? 84c0 }
            // n = 7, score = 100
            //   8d4dd0               | lea                 ecx, [ebp - 0x30]
            //   ba01000000           | mov                 edx, 1
            //   0fb63c38             | movzx               edi, byte ptr [eax + edi]
            //   8b45ac               | mov                 eax, dword ptr [ebp - 0x54]
            //   c1e710               | shl                 edi, 0x10
            //   e8????????           |                     
            //   84c0                 | test                al, al

        $sequence_2 = { e8???????? 51 51 8b06 39c7 0f848b000000 85c0 }
            // n = 7, score = 100
            //   e8????????           |                     
            //   51                   | push                ecx
            //   51                   | push                ecx
            //   8b06                 | mov                 eax, dword ptr [esi]
            //   39c7                 | cmp                 edi, eax
            //   0f848b000000         | je                  0x91
            //   85c0                 | test                eax, eax

        $sequence_3 = { d9c9 dbe9 7a02 7438 dce9 d9ee dbf2 }
            // n = 7, score = 100
            //   d9c9                 | fxch                st(1)
            //   dbe9                 | fucomi              st(1)
            //   7a02                 | jp                  4
            //   7438                 | je                  0x3a
            //   dce9                 | fsub                st(1), st(0)
            //   d9ee                 | fldz                
            //   dbf2                 | fcomi               st(2)

        $sequence_4 = { c705????????00ae4200 c705????????fa5b4100 c705????????00000000 c705????????01000000 c705????????01000000 66c705????????0e03 8b0c8540e94100 }
            // n = 7, score = 100
            //   c705????????00ae4200     |     
            //   c705????????fa5b4100     |     
            //   c705????????00000000     |     
            //   c705????????01000000     |     
            //   c705????????01000000     |     
            //   66c705????????0e03     |     
            //   8b0c8540e94100       | mov                 ecx, dword ptr [eax*4 + 0x41e940]

        $sequence_5 = { e8???????? 8975d4 eb2d 807dcf00 8b75e4 740a 8b4b68 }
            // n = 7, score = 100
            //   e8????????           |                     
            //   8975d4               | mov                 dword ptr [ebp - 0x2c], esi
            //   eb2d                 | jmp                 0x2f
            //   807dcf00             | cmp                 byte ptr [ebp - 0x31], 0
            //   8b75e4               | mov                 esi, dword ptr [ebp - 0x1c]
            //   740a                 | je                  0xc
            //   8b4b68               | mov                 ecx, dword ptr [ebx + 0x68]

        $sequence_6 = { 31d2 e8???????? c7442408d8030000 ba???????? 89d9 c7442404???????? c70424???????? }
            // n = 7, score = 100
            //   31d2                 | xor                 edx, edx
            //   e8????????           |                     
            //   c7442408d8030000     | mov                 dword ptr [esp + 8], 0x3d8
            //   ba????????           |                     
            //   89d9                 | mov                 ecx, ebx
            //   c7442404????????     |                     
            //   c70424????????       |                     

        $sequence_7 = { c605????????02 c705????????40004200 c705????????f0004200 c705????????04000000 c705????????04000000 c605????????18 c705????????808b4200 }
            // n = 7, score = 100
            //   c605????????02       |                     
            //   c705????????40004200     |     
            //   c705????????f0004200     |     
            //   c705????????04000000     |     
            //   c705????????04000000     |     
            //   c605????????18       |                     
            //   c705????????808b4200     |     

        $sequence_8 = { 0f8591000000 8b5310 8b430c 85d2 740e 8b12 85d2 }
            // n = 7, score = 100
            //   0f8591000000         | jne                 0x97
            //   8b5310               | mov                 edx, dword ptr [ebx + 0x10]
            //   8b430c               | mov                 eax, dword ptr [ebx + 0xc]
            //   85d2                 | test                edx, edx
            //   740e                 | je                  0x10
            //   8b12                 | mov                 edx, dword ptr [edx]
            //   85d2                 | test                edx, edx

        $sequence_9 = { 2345d0 8945d4 8b03 85c0 740a 8b00 }
            // n = 6, score = 100
            //   2345d0               | and                 eax, dword ptr [ebp - 0x30]
            //   8945d4               | mov                 dword ptr [ebp - 0x2c], eax
            //   8b03                 | mov                 eax, dword ptr [ebx]
            //   85c0                 | test                eax, eax
            //   740a                 | je                  0xc
            //   8b00                 | mov                 eax, dword ptr [eax]

    condition:
        7 of them and filesize < 919552
}
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