SYMBOLCOMMON_NAMEaka. SYNONYMS
win.grillmark (Back to overview)

GRILLMARK

aka: Hellsing Backdoor

Actor(s): Hellsing, Leviathan


This is a proxy-aware HTTP backdoor that is implemented as a service and uses the compromised system's proxy settings to access the internet. C&C traffic is base64 encoded and the files sent to the server are compressed with aPLib.

References
2019-04-11FireEyeFireEye
@online{fireeye:20190411:mtrend:597b240, author = {FireEye}, title = {{M-Trend 2019}}, date = {2019-04-11}, organization = {FireEye}, url = {https://content.fireeye.com/m-trends/rpt-m-trends-2019}, language = {English}, urldate = {2020-01-10} } M-Trend 2019
GRILLMARK
2015-04-15Kaspersky LabsCostin Raiu, Maxim Golovkin
@online{raiu:20150415:chronicles:aa4af84, author = {Costin Raiu and Maxim Golovkin}, title = {{The Chronicles of the Hellsing APT: the Empire Strikes Back}}, date = {2015-04-15}, organization = {Kaspersky Labs}, url = {https://securelist.com/the-chronicles-of-the-hellsing-apt-the-empire-strikes-back/69567/}, language = {English}, urldate = {2021-02-06} } The Chronicles of the Hellsing APT: the Empire Strikes Back
GRILLMARK Hellsing
Yara Rules
[TLP:WHITE] win_grillmark_auto (20220808 | Detects win.grillmark.)
rule win_grillmark_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2022-08-05"
        version = "1"
        description = "Detects win.grillmark."
        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.grillmark"
        malpedia_rule_date = "20220805"
        malpedia_hash = "6ec06c64bcfdbeda64eff021c766b4ce34542b71"
        malpedia_version = "20220808"
        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 = { 50 8d85f8fdffff 50 ff15???????? 8d85fcfeffff 50 }
            // n = 6, score = 300
            //   50                   | push                eax
            //   8d85f8fdffff         | lea                 eax, [ebp - 0x208]
            //   50                   | push                eax
            //   ff15????????         |                     
            //   8d85fcfeffff         | lea                 eax, [ebp - 0x104]
            //   50                   | push                eax

        $sequence_1 = { 33c0 8d7d98 895d94 f3ab 8d7ddc 895dd8 ab }
            // n = 7, score = 300
            //   33c0                 | xor                 eax, eax
            //   8d7d98               | lea                 edi, [ebp - 0x68]
            //   895d94               | mov                 dword ptr [ebp - 0x6c], ebx
            //   f3ab                 | rep stosd           dword ptr es:[edi], eax
            //   8d7ddc               | lea                 edi, [ebp - 0x24]
            //   895dd8               | mov                 dword ptr [ebp - 0x28], ebx
            //   ab                   | stosd               dword ptr es:[edi], eax

        $sequence_2 = { 57 8d85fcfeffff 6a00 50 e8???????? ff7514 }
            // n = 6, score = 300
            //   57                   | push                edi
            //   8d85fcfeffff         | lea                 eax, [ebp - 0x104]
            //   6a00                 | push                0
            //   50                   | push                eax
            //   e8????????           |                     
            //   ff7514               | push                dword ptr [ebp + 0x14]

        $sequence_3 = { 3bfb 0f84dd000000 8d4584 68000000a0 50 e8???????? 59 }
            // n = 7, score = 300
            //   3bfb                 | cmp                 edi, ebx
            //   0f84dd000000         | je                  0xe3
            //   8d4584               | lea                 eax, [ebp - 0x7c]
            //   68000000a0           | push                0xa0000000
            //   50                   | push                eax
            //   e8????????           |                     
            //   59                   | pop                 ecx

        $sequence_4 = { ffb54cffffff 50 53 68???????? }
            // n = 4, score = 300
            //   ffb54cffffff         | push                dword ptr [ebp - 0xb4]
            //   50                   | push                eax
            //   53                   | push                ebx
            //   68????????           |                     

        $sequence_5 = { 80f920 741f 80f922 752f 84d2 }
            // n = 5, score = 300
            //   80f920               | cmp                 cl, 0x20
            //   741f                 | je                  0x21
            //   80f922               | cmp                 cl, 0x22
            //   752f                 | jne                 0x31
            //   84d2                 | test                dl, dl

        $sequence_6 = { 837dfc03 0f855a010000 6830030000 6a40 ff15???????? 56 50 }
            // n = 7, score = 300
            //   837dfc03             | cmp                 dword ptr [ebp - 4], 3
            //   0f855a010000         | jne                 0x160
            //   6830030000           | push                0x330
            //   6a40                 | push                0x40
            //   ff15????????         |                     
            //   56                   | push                esi
            //   50                   | push                eax

        $sequence_7 = { eb0f 2bc6 50 56 ff750c }
            // n = 5, score = 300
            //   eb0f                 | jmp                 0x11
            //   2bc6                 | sub                 eax, esi
            //   50                   | push                eax
            //   56                   | push                esi
            //   ff750c               | push                dword ptr [ebp + 0xc]

        $sequence_8 = { 59 43 ff750c 6a00 e8???????? 8bf8 }
            // n = 6, score = 300
            //   59                   | pop                 ecx
            //   43                   | inc                 ebx
            //   ff750c               | push                dword ptr [ebp + 0xc]
            //   6a00                 | push                0
            //   e8????????           |                     
            //   8bf8                 | mov                 edi, eax

        $sequence_9 = { 8b55f4 ff45f0 8345f404 893a ff45f8 880f 47 }
            // n = 7, score = 300
            //   8b55f4               | mov                 edx, dword ptr [ebp - 0xc]
            //   ff45f0               | inc                 dword ptr [ebp - 0x10]
            //   8345f404             | add                 dword ptr [ebp - 0xc], 4
            //   893a                 | mov                 dword ptr [edx], edi
            //   ff45f8               | inc                 dword ptr [ebp - 8]
            //   880f                 | mov                 byte ptr [edi], cl
            //   47                   | inc                 edi

    condition:
        7 of them and filesize < 212992
}
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