SYMBOLCOMMON_NAMEaka. SYNONYMS
win.rarstar (Back to overview)

rarstar

Actor(s): Tick


This ransomware encrypts all user’s data on the PC (photos, documents, excel tables, music, videos, etc), adds its specific extension to every file, and creates the HOW_TO_DECYPHER_FILES.txt files in every folder which contains encrypted files.

References
2017-10-12SecureworksCTU Research Team
@online{team:20171012:bronze:7b9ae02, author = {CTU Research Team}, title = {{BRONZE BUTLER Targets Japanese Enterprises}}, date = {2017-10-12}, organization = {Secureworks}, url = {https://www.secureworks.com/research/bronze-butler-targets-japanese-businesses}, language = {English}, urldate = {2020-01-07} } BRONZE BUTLER Targets Japanese Enterprises
Daserf Datper rarstar xxmm Tick
Yara Rules
[TLP:WHITE] win_rarstar_auto (20230125 | Detects win.rarstar.)
rule win_rarstar_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2023-01-25"
        version = "1"
        description = "Detects win.rarstar."
        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.rarstar"
        malpedia_rule_date = "20230124"
        malpedia_hash = "2ee0eebba83dce3d019a90519f2f972c0fcf9686"
        malpedia_version = "20230125"
        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 = { 51 ff15???????? 8d942428060000 8d442414 }
            // n = 4, score = 100
            //   51                   | push                ecx
            //   ff15????????         |                     
            //   8d942428060000       | lea                 edx, [esp + 0x628]
            //   8d442414             | lea                 eax, [esp + 0x14]

        $sequence_1 = { 89542410 89442434 89542414 89442438 }
            // n = 4, score = 100
            //   89542410             | mov                 dword ptr [esp + 0x10], edx
            //   89442434             | mov                 dword ptr [esp + 0x34], eax
            //   89542414             | mov                 dword ptr [esp + 0x14], edx
            //   89442438             | mov                 dword ptr [esp + 0x38], eax

        $sequence_2 = { 83e303 0bd3 41 8a9230924000 }
            // n = 4, score = 100
            //   83e303               | and                 ebx, 3
            //   0bd3                 | or                  edx, ebx
            //   41                   | inc                 ecx
            //   8a9230924000         | mov                 dl, byte ptr [edx + 0x409230]

        $sequence_3 = { 52 ffd5 8d842418010000 68???????? 50 ffd6 }
            // n = 6, score = 100
            //   52                   | push                edx
            //   ffd5                 | call                ebp
            //   8d842418010000       | lea                 eax, [esp + 0x118]
            //   68????????           |                     
            //   50                   | push                eax
            //   ffd6                 | call                esi

        $sequence_4 = { 33db 8a940c24010000 8a5c0c24 03c2 03c3 25ff000080 }
            // n = 6, score = 100
            //   33db                 | xor                 ebx, ebx
            //   8a940c24010000       | mov                 dl, byte ptr [esp + ecx + 0x124]
            //   8a5c0c24             | mov                 bl, byte ptr [esp + ecx + 0x24]
            //   03c2                 | add                 eax, edx
            //   03c3                 | add                 eax, ebx
            //   25ff000080           | and                 eax, 0x800000ff

        $sequence_5 = { 5e c3 8b4c2408 ff4904 780e 8b11 8a442404 }
            // n = 7, score = 100
            //   5e                   | pop                 esi
            //   c3                   | ret                 
            //   8b4c2408             | mov                 ecx, dword ptr [esp + 8]
            //   ff4904               | dec                 dword ptr [ecx + 4]
            //   780e                 | js                  0x10
            //   8b11                 | mov                 edx, dword ptr [ecx]
            //   8a442404             | mov                 al, byte ptr [esp + 4]

        $sequence_6 = { e8???????? 6a02 6a00 57 8944243c }
            // n = 5, score = 100
            //   e8????????           |                     
            //   6a02                 | push                2
            //   6a00                 | push                0
            //   57                   | push                edi
            //   8944243c             | mov                 dword ptr [esp + 0x3c], eax

        $sequence_7 = { 899c2424030000 f3a5 8bc8 83e103 33c0 f3a4 }
            // n = 6, score = 100
            //   899c2424030000       | mov                 dword ptr [esp + 0x324], ebx
            //   f3a5                 | rep movsd           dword ptr es:[edi], dword ptr [esi]
            //   8bc8                 | mov                 ecx, eax
            //   83e103               | and                 ecx, 3
            //   33c0                 | xor                 eax, eax
            //   f3a4                 | rep movsb           byte ptr es:[edi], byte ptr [esi]

        $sequence_8 = { e8???????? 8b442420 83c40c 48 89442414 }
            // n = 5, score = 100
            //   e8????????           |                     
            //   8b442420             | mov                 eax, dword ptr [esp + 0x20]
            //   83c40c               | add                 esp, 0xc
            //   48                   | dec                 eax
            //   89442414             | mov                 dword ptr [esp + 0x14], eax

        $sequence_9 = { 0f8412010000 85f6 779a 8b5c241c 6a00 }
            // n = 5, score = 100
            //   0f8412010000         | je                  0x118
            //   85f6                 | test                esi, esi
            //   779a                 | ja                  0xffffff9c
            //   8b5c241c             | mov                 ebx, dword ptr [esp + 0x1c]
            //   6a00                 | push                0

    condition:
        7 of them and filesize < 122880
}
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