SYMBOLCOMMON_NAMEaka. SYNONYMS
win.grimagent (Back to overview)

GRIMAGENT

Actor(s): UNC1878


GRIMAGENT is a backdoor that can execute arbitrary commands, download files, create and delete scheduled tasks, and execute programs via scheduled tasks or via the ShellExecute API. The malware persists via a randomly named scheduled task and a registry Run key. The backdoor communicates to hard-coded C&C servers via HTTP requests with portions of its network communications encrypted using both asymmetric and symmetric cryptography. GRIMAGENT was used during some Ryuk Ransomware intrusions in 2020.

References
2021-10-07MandiantJoshua Shilko, Zach Riddle, Jennifer Brooks, Genevieve Stark, Adam Brunner, Kimberly Goody, Jeremy Kennelly
@online{shilko:20211007:fin12:43d89f5, author = {Joshua Shilko and Zach Riddle and Jennifer Brooks and Genevieve Stark and Adam Brunner and Kimberly Goody and Jeremy Kennelly}, title = {{FIN12: The Prolific Ransomware Intrusion Threat Actor That Has Aggressively Pursued Healthcare Targets}}, date = {2021-10-07}, organization = {Mandiant}, url = {https://www.mandiant.com/resources/fin12-ransomware-intrusion-actor-pursuing-healthcare-targets}, language = {English}, urldate = {2021-10-08} } FIN12: The Prolific Ransomware Intrusion Threat Actor That Has Aggressively Pursued Healthcare Targets
BazarBackdoor GRIMAGENT Ryuk
2021-07-02Group-IBGroup-IB
@online{groupib:20210702:brothers:0b68ead, author = {Group-IB}, title = {{The Brothers Grim - The reversing tale of GrimAgent malware used by Ryuk}}, date = {2021-07-02}, organization = {Group-IB}, url = {https://gibnc.group-ib.com/s/Group-IB_GrimAgent_analysis#pdfviewer}, language = {English}, urldate = {2021-07-06} } The Brothers Grim - The reversing tale of GrimAgent malware used by Ryuk
GRIMAGENT
2021-07-02Group-IBAlbert Priego
@online{priego:20210702:brothers:74e06d3, author = {Albert Priego}, title = {{The Brothers Grim - The reversing tale of GrimAgent malware used by Ryuk}}, date = {2021-07-02}, organization = {Group-IB}, url = {https://blog.group-ib.com/grimagent}, language = {English}, urldate = {2021-07-05} } The Brothers Grim - The reversing tale of GrimAgent malware used by Ryuk
GRIMAGENT
2021-01-22Twitter (@bryceabdo)Bryce
@online{bryce:20210122:grimagent:611b917, author = {Bryce}, title = {{Tweet on GRIMAGENT malware used by UNC1878 during some #RYUK intrusions in 2020}}, date = {2021-01-22}, organization = {Twitter (@bryceabdo)}, url = {https://twitter.com/bryceabdo/status/1352359414746009608}, language = {English}, urldate = {2021-02-06} } Tweet on GRIMAGENT malware used by UNC1878 during some #RYUK intrusions in 2020
GRIMAGENT
Yara Rules
[TLP:WHITE] win_grimagent_auto (20230125 | Detects win.grimagent.)
rule win_grimagent_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2023-01-25"
        version = "1"
        description = "Detects win.grimagent."
        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.grimagent"
        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 = { 83c0ff 898548f9ffff 8b8d48f9ffff 8a5101 8895d8f9ffff 838548f9ffff01 80bdd8f9ffff00 }
            // n = 7, score = 100
            //   83c0ff               | add                 eax, -1
            //   898548f9ffff         | mov                 dword ptr [ebp - 0x6b8], eax
            //   8b8d48f9ffff         | mov                 ecx, dword ptr [ebp - 0x6b8]
            //   8a5101               | mov                 dl, byte ptr [ecx + 1]
            //   8895d8f9ffff         | mov                 byte ptr [ebp - 0x628], dl
            //   838548f9ffff01       | add                 dword ptr [ebp - 0x6b8], 1
            //   80bdd8f9ffff00       | cmp                 byte ptr [ebp - 0x628], 0

        $sequence_1 = { e9???????? 8b8d04fbffff 51 6a00 8b950cfbffff 52 e8???????? }
            // n = 7, score = 100
            //   e9????????           |                     
            //   8b8d04fbffff         | mov                 ecx, dword ptr [ebp - 0x4fc]
            //   51                   | push                ecx
            //   6a00                 | push                0
            //   8b950cfbffff         | mov                 edx, dword ptr [ebp - 0x4f4]
            //   52                   | push                edx
            //   e8????????           |                     

        $sequence_2 = { 6a15 6878b94200 e8???????? 83c410 6a14 6858834200 6a15 }
            // n = 7, score = 100
            //   6a15                 | push                0x15
            //   6878b94200           | push                0x42b978
            //   e8????????           |                     
            //   83c410               | add                 esp, 0x10
            //   6a14                 | push                0x14
            //   6858834200           | push                0x428358
            //   6a15                 | push                0x15

        $sequence_3 = { 889578f4ffff 838598f3ffff01 80bd78f4ffff00 75e1 8bbd98f3ffff 8bb5e0f2ffff 8b85dcf2ffff }
            // n = 7, score = 100
            //   889578f4ffff         | mov                 byte ptr [ebp - 0xb88], dl
            //   838598f3ffff01       | add                 dword ptr [ebp - 0xc68], 1
            //   80bd78f4ffff00       | cmp                 byte ptr [ebp - 0xb88], 0
            //   75e1                 | jne                 0xffffffe3
            //   8bbd98f3ffff         | mov                 edi, dword ptr [ebp - 0xc68]
            //   8bb5e0f2ffff         | mov                 esi, dword ptr [ebp - 0xd20]
            //   8b85dcf2ffff         | mov                 eax, dword ptr [ebp - 0xd24]

        $sequence_4 = { c78560abffff28010000 8b8560abffff 50 6a00 8d8d24feffff 51 e8???????? }
            // n = 7, score = 100
            //   c78560abffff28010000     | mov    dword ptr [ebp - 0x54a0], 0x128
            //   8b8560abffff         | mov                 eax, dword ptr [ebp - 0x54a0]
            //   50                   | push                eax
            //   6a00                 | push                0
            //   8d8d24feffff         | lea                 ecx, [ebp - 0x1dc]
            //   51                   | push                ecx
            //   e8????????           |                     

        $sequence_5 = { 6a03 68f8854200 6a15 6878b94200 e8???????? 83c410 6a01 }
            // n = 7, score = 100
            //   6a03                 | push                3
            //   68f8854200           | push                0x4285f8
            //   6a15                 | push                0x15
            //   6878b94200           | push                0x42b978
            //   e8????????           |                     
            //   83c410               | add                 esp, 0x10
            //   6a01                 | push                1

        $sequence_6 = { 8b8d20abffff 898d50abffff 6a00 8d9550abffff 52 6a00 6a00 }
            // n = 7, score = 100
            //   8b8d20abffff         | mov                 ecx, dword ptr [ebp - 0x54e0]
            //   898d50abffff         | mov                 dword ptr [ebp - 0x54b0], ecx
            //   6a00                 | push                0
            //   8d9550abffff         | lea                 edx, [ebp - 0x54b0]
            //   52                   | push                edx
            //   6a00                 | push                0
            //   6a00                 | push                0

        $sequence_7 = { ff15???????? 898508fbffff 83bd08fbffffff 7532 6800800000 6a00 8b850cfbffff }
            // n = 7, score = 100
            //   ff15????????         |                     
            //   898508fbffff         | mov                 dword ptr [ebp - 0x4f8], eax
            //   83bd08fbffffff       | cmp                 dword ptr [ebp - 0x4f8], -1
            //   7532                 | jne                 0x34
            //   6800800000           | push                0x8000
            //   6a00                 | push                0
            //   8b850cfbffff         | mov                 eax, dword ptr [ebp - 0x4f4]

        $sequence_8 = { 668b85a0f9ffff 668902 8b8de8f8ffff 83c102 898de8f8ffff 8b9550f9ffff 83c202 }
            // n = 7, score = 100
            //   668b85a0f9ffff       | mov                 ax, word ptr [ebp - 0x660]
            //   668902               | mov                 word ptr [edx], ax
            //   8b8de8f8ffff         | mov                 ecx, dword ptr [ebp - 0x718]
            //   83c102               | add                 ecx, 2
            //   898de8f8ffff         | mov                 dword ptr [ebp - 0x718], ecx
            //   8b9550f9ffff         | mov                 edx, dword ptr [ebp - 0x6b0]
            //   83c202               | add                 edx, 2

        $sequence_9 = { d1f9 898d80f8ffff 8b9580f8ffff 8b85f4f9ffff 668b0d???????? 66898c5008100000 8d950cfdffff }
            // n = 7, score = 100
            //   d1f9                 | sar                 ecx, 1
            //   898d80f8ffff         | mov                 dword ptr [ebp - 0x780], ecx
            //   8b9580f8ffff         | mov                 edx, dword ptr [ebp - 0x780]
            //   8b85f4f9ffff         | mov                 eax, dword ptr [ebp - 0x60c]
            //   668b0d????????       |                     
            //   66898c5008100000     | mov                 word ptr [eax + edx*2 + 0x1008], cx
            //   8d950cfdffff         | lea                 edx, [ebp - 0x2f4]

    condition:
        7 of them and filesize < 582656
}
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