SYMBOLCOMMON_NAMEaka. SYNONYMS
win.cryptomix (Back to overview)

CryptoMix

aka: CryptFile2

A variant of CryptoMix is win.clop.

References
2020-03-04SentinelOneJason Reaves
@online{reaves:20200304:breaking:8262e7e, author = {Jason Reaves}, title = {{Breaking TA505’s Crypter with an SMT Solver}}, date = {2020-03-04}, organization = {SentinelOne}, url = {https://labs.sentinelone.com/breaking-ta505s-crypter-with-an-smt-solver/}, language = {English}, urldate = {2020-03-04} } Breaking TA505’s Crypter with an SMT Solver
Clop CryptoMix MINEBRIDGE
2017-12-13Bleeping ComputerLawrence Abrams
@online{abrams:20171213:work:d439b4b, author = {Lawrence Abrams}, title = {{WORK Cryptomix Ransomware Variant Released}}, date = {2017-12-13}, organization = {Bleeping Computer}, url = {https://www.bleepingcomputer.com/news/security/work-cryptomix-ransomware-variant-released/}, language = {English}, urldate = {2019-12-20} } WORK Cryptomix Ransomware Variant Released
CryptoMix
2017-01-04CERT.PLJarosław Jedynak
@online{jedynak:20170104:technical:9cf0ab7, author = {Jarosław Jedynak}, title = {{Technical analysis of CryptoMix/CryptFile2 ransomware}}, date = {2017-01-04}, organization = {CERT.PL}, url = {https://www.cert.pl/en/news/single/technical-analysis-of-cryptomixcryptfile2-ransomware/}, language = {English}, urldate = {2020-01-13} } Technical analysis of CryptoMix/CryptFile2 ransomware
CryptoMix
Yara Rules
[TLP:WHITE] win_cryptomix_auto (20201023 | autogenerated rule brought to you by yara-signator)
rule win_cryptomix_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2020-12-22"
        version = "1"
        description = "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.cryptomix"
        malpedia_rule_date = "20201222"
        malpedia_hash = "30354d830a29f0fbd3714d93d94dea941d77a130"
        malpedia_version = "20201023"
        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 = { 68f37443c5 6a01 e8???????? 59 }
            // n = 4, score = 200
            //   68f37443c5           | push                0xc54374f3
            //   6a01                 | push                1
            //   e8????????           |                     
            //   59                   | pop                 ecx

        $sequence_1 = { 85c0 7507 55 e8???????? }
            // n = 4, score = 200
            //   85c0                 | test                eax, eax
            //   7507                 | jne                 9
            //   55                   | push                ebp
            //   e8????????           |                     

        $sequence_2 = { 8b30 57 8b7dfc 68dee70218 }
            // n = 4, score = 200
            //   8b30                 | mov                 esi, dword ptr [eax]
            //   57                   | push                edi
            //   8b7dfc               | mov                 edi, dword ptr [ebp - 4]
            //   68dee70218           | push                0x1802e7de

        $sequence_3 = { ffb5e8fbffff ff15???????? ffb5e8fbffff 8937 ff15???????? 8b4dfc }
            // n = 6, score = 200
            //   ffb5e8fbffff         | push                dword ptr [ebp - 0x418]
            //   ff15????????         |                     
            //   ffb5e8fbffff         | push                dword ptr [ebp - 0x418]
            //   8937                 | mov                 dword ptr [edi], esi
            //   ff15????????         |                     
            //   8b4dfc               | mov                 ecx, dword ptr [ebp - 4]

        $sequence_4 = { 83c40c 8d8591efffff 68ff010000 6a00 50 c68590efffff00 }
            // n = 6, score = 200
            //   83c40c               | add                 esp, 0xc
            //   8d8591efffff         | lea                 eax, [ebp - 0x106f]
            //   68ff010000           | push                0x1ff
            //   6a00                 | push                0
            //   50                   | push                eax
            //   c68590efffff00       | mov                 byte ptr [ebp - 0x1070], 0

        $sequence_5 = { 85c0 0f856fffffff 56 ff15???????? }
            // n = 4, score = 200
            //   85c0                 | test                eax, eax
            //   0f856fffffff         | jne                 0xffffff75
            //   56                   | push                esi
            //   ff15????????         |                     

        $sequence_6 = { 8d8decfdffff 51 33f6 56 ffd0 }
            // n = 5, score = 200
            //   8d8decfdffff         | lea                 ecx, [ebp - 0x214]
            //   51                   | push                ecx
            //   33f6                 | xor                 esi, esi
            //   56                   | push                esi
            //   ffd0                 | call                eax

        $sequence_7 = { 85c0 752e 56 8b75fc }
            // n = 4, score = 200
            //   85c0                 | test                eax, eax
            //   752e                 | jne                 0x30
            //   56                   | push                esi
            //   8b75fc               | mov                 esi, dword ptr [ebp - 4]

        $sequence_8 = { ffd0 68???????? 50 e8???????? 59 }
            // n = 5, score = 200
            //   ffd0                 | call                eax
            //   68????????           |                     
            //   50                   | push                eax
            //   e8????????           |                     
            //   59                   | pop                 ecx

        $sequence_9 = { 8945fc 8b4508 53 56 57 8bf2 8bd9 }
            // n = 7, score = 200
            //   8945fc               | mov                 dword ptr [ebp - 4], eax
            //   8b4508               | mov                 eax, dword ptr [ebp + 8]
            //   53                   | push                ebx
            //   56                   | push                esi
            //   57                   | push                edi
            //   8bf2                 | mov                 esi, edx
            //   8bd9                 | mov                 ebx, ecx

        $sequence_10 = { ff15???????? 8b1d???????? 8bb58cefffff ffb580efffff }
            // n = 4, score = 200
            //   ff15????????         |                     
            //   8b1d????????         |                     
            //   8bb58cefffff         | mov                 esi, dword ptr [ebp - 0x1074]
            //   ffb580efffff         | push                dword ptr [ebp - 0x1080]

        $sequence_11 = { 7403 50 eb46 6a00 6880000000 6a02 6a00 }
            // n = 7, score = 200
            //   7403                 | je                  5
            //   50                   | push                eax
            //   eb46                 | jmp                 0x48
            //   6a00                 | push                0
            //   6880000000           | push                0x80
            //   6a02                 | push                2
            //   6a00                 | push                0

        $sequence_12 = { 66a5 a4 0f848c000000 48 7476 48 7460 }
            // n = 7, score = 200
            //   66a5                 | movsw               word ptr es:[edi], word ptr [esi]
            //   a4                   | movsb               byte ptr es:[edi], byte ptr [esi]
            //   0f848c000000         | je                  0x92
            //   48                   | dec                 eax
            //   7476                 | je                  0x78
            //   48                   | dec                 eax
            //   7460                 | je                  0x62

        $sequence_13 = { 83f814 752c 8d8590efffff 50 a1???????? }
            // n = 5, score = 200
            //   83f814               | cmp                 eax, 0x14
            //   752c                 | jne                 0x2e
            //   8d8590efffff         | lea                 eax, [ebp - 0x1070]
            //   50                   | push                eax
            //   a1????????           |                     

        $sequence_14 = { 6a08 e8???????? 59 59 8d8d60feffff 51 6802020000 }
            // n = 7, score = 200
            //   6a08                 | push                8
            //   e8????????           |                     
            //   59                   | pop                 ecx
            //   59                   | pop                 ecx
            //   8d8d60feffff         | lea                 ecx, [ebp - 0x1a0]
            //   51                   | push                ecx
            //   6802020000           | push                0x202

        $sequence_15 = { 68???????? 68???????? ffd3 56 68???????? ffd7 8d8598f9ffff }
            // n = 7, score = 200
            //   68????????           |                     
            //   68????????           |                     
            //   ffd3                 | call                ebx
            //   56                   | push                esi
            //   68????????           |                     
            //   ffd7                 | call                edi
            //   8d8598f9ffff         | lea                 eax, [ebp - 0x668]

    condition:
        7 of them and filesize < 188416
}
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