SYMBOLCOMMON_NAMEaka. SYNONYMS
win.skip20 (Back to overview)

skip-2.0

Actor(s): APT41


A Microsoft SQL Server backdoor

References
2019-10-21ESET ResearchMathieu Tartare
@online{tartare:20191021:winnti:eb2c722, author = {Mathieu Tartare}, title = {{Winnti Group’s skip‑2.0: A Microsoft SQL Server backdoor}}, date = {2019-10-21}, organization = {ESET Research}, url = {https://www.welivesecurity.com/2019/10/21/winnti-group-skip2-0-microsoft-sql-server-backdoor/}, language = {English}, urldate = {2019-11-14} } Winnti Group’s skip‑2.0: A Microsoft SQL Server backdoor
LOWKEY skip-2.0
Yara Rules
[TLP:WHITE] win_skip20_auto (20220411 | Detects win.skip20.)
rule win_skip20_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2022-04-08"
        version = "1"
        description = "Detects win.skip20."
        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.skip20"
        malpedia_rule_date = "20220405"
        malpedia_hash = "ecd38294bd47d5589be5cd5490dc8bb4804afc2a"
        malpedia_version = "20220411"
        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 = { 0f88f9f5ffff 488b4510 4c8d15b794ffff 8b08 894b08 4883451004 e9???????? }
            // n = 7, score = 200
            //   0f88f9f5ffff         | mov                 edx, edi
            //   488b4510             | dec                 eax
            //   4c8d15b794ffff       | mov                 ecx, ebx
            //   8b08                 | mov                 dl, 0x5d
            //   894b08               | dec                 eax
            //   4883451004           | mov                 ecx, ebx
            //   e9????????           |                     

        $sequence_1 = { 740d b801000000 66d3e0 664109402c 4589584c ffca 49ffc2 }
            // n = 7, score = 200
            //   740d                 | bts                 eax, 0x19
            //   b801000000           | or                  dword ptr [esi + 4], 0x4000
            //   66d3e0               | inc                 esp
            //   664109402c           | mov                 eax, dword ptr [ebp + 0x1c]
            //   4589584c             | dec                 esp
            //   ffca                 | mov                 ecx, ebx
            //   49ffc2               | dec                 eax

        $sequence_2 = { ff15???????? eb41 ba0e000000 488bcb e8???????? 4885c0 0f847affffff }
            // n = 7, score = 200
            //   ff15????????         |                     
            //   eb41                 | dec                 ebp
            //   ba0e000000           | add                 eax, ebp
            //   488bcb               | dec                 eax
            //   e8????????           |                     
            //   4885c0               | mov                 ecx, ebx
            //   0f847affffff         | mov                 dword ptr [esp + 0x48], esi

        $sequence_3 = { 740a 418bc1 66d3e0 6609422c }
            // n = 4, score = 200
            //   740a                 | dec                 eax
            //   418bc1               | lea                 ecx, dword ptr [eax + ecx + 4]
            //   66d3e0               | dec                 eax
            //   6609422c             | add                 edx, 4

        $sequence_4 = { 440fb648ff 4989442410 0fbae61d 7357 4180f920 725c 488b542468 }
            // n = 7, score = 200
            //   440fb648ff           | dec                 ecx
            //   4989442410           | mov                 ecx, eax
            //   0fbae61d             | inc                 ecx
            //   7357                 | cmp                 byte ptr [eax], bl
            //   4180f920             | dec                 esp
            //   725c                 | lea                 ebx, dword ptr [0x1ffbd]
            //   488b542468           | dec                 ebp

        $sequence_5 = { 7435 4180c410 41b820000000 448864bb23 66448944bb24 e9???????? b840000000 }
            // n = 7, score = 200
            //   7435                 | mov                 eax, ebx
            //   4180c410             | inc                 ecx
            //   41b820000000         | cmp                 ecx, 1
            //   448864bb23           | inc                 ecx
            //   66448944bb24         | cmove               eax, esi
            //   e9????????           |                     
            //   b840000000           | mov                 dword ptr [esp + 0x58], eax

        $sequence_6 = { 57 4883ec20 bf24000000 488d1d9c330100 8bf7 488b2b 4885ed }
            // n = 7, score = 200
            //   57                   | mov                 dword ptr [esp + 0x25c], 0xc3c28b48
            //   4883ec20             | mov                 word ptr [esp + 0x260], 0x9090
            //   bf24000000           | mov                 byte ptr [esp + 0x262], 0x90
            //   488d1d9c330100       | mov                 dword ptr [esp + 0x254], 0xfc
            //   8bf7                 | mov                 dword ptr [esp + 0x258], 0x1b
            //   488b2b               | mov                 dword ptr [esp + 0x25c], 0xc3c28b48
            //   4885ed               | mov                 word ptr [esp + 0x260], 0x9090

        $sequence_7 = { 6685c9 7503 33c0 c3 0fb7c1 ba00e00000 }
            // n = 6, score = 200
            //   6685c9               | mov                 dword ptr [esp + 0x50], 0
            //   7503                 | inc                 esp
            //   33c0                 | mov                 dword ptr [esp + 0x48], ebp
            //   c3                   | je                  0x14
            //   0fb7c1               | mov                 ecx, 0x200
            //   ba00e00000           | inc                 esp

        $sequence_8 = { 440fb75c2476 89442440 894c2438 89542430 4489542428 44895c2420 488d15c32b0100 }
            // n = 7, score = 200
            //   440fb75c2476         | mov                 ecx, ebx
            //   89442440             | dec                 eax
            //   894c2438             | test                eax, eax
            //   89542430             | je                  0x2e7
            //   4489542428           | dec                 esp
            //   44895c2420           | lea                 eax, dword ptr [esp + 0x2e8]
            //   488d15c32b0100       | mov                 edx, edi

        $sequence_9 = { 4c89742430 83fe0f 0f8442020000 837db302 754e 8b4dbf 0fbae119 }
            // n = 7, score = 200
            //   4c89742430           | inc                 cx
            //   83fe0f               | cmp                 eax, esp
            //   0f8442020000         | je                  0x1919
            //   837db302             | mov                 ecx, 0x133
            //   754e                 | mov                 ecx, 0x2d
            //   8b4dbf               | cmovl               edx, ecx
            //   0fbae119             | dec                 eax

    condition:
        7 of them and filesize < 794624
}
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