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 (20211008 | Detects win.grimagent.)
rule win_grimagent_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2021-10-07"
        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 = "20211007"
        malpedia_hash = "e5b790e0f888f252d49063a1251ca60ec2832535"
        malpedia_version = "20211008"
        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 = { c745f800000000 c785d0feffff28010000 6a00 6a02 e8???????? 8945fc }
            // n = 6, score = 100
            //   c745f800000000       | mov                 dword ptr [ebp - 8], 0
            //   c785d0feffff28010000     | mov    dword ptr [ebp - 0x130], 0x128
            //   6a00                 | push                0
            //   6a02                 | push                2
            //   e8????????           |                     
            //   8945fc               | mov                 dword ptr [ebp - 4], eax

        $sequence_1 = { 51 e8???????? 85c0 7434 8d95d0feffff }
            // n = 5, score = 100
            //   51                   | push                ecx
            //   e8????????           |                     
            //   85c0                 | test                eax, eax
            //   7434                 | je                  0x36
            //   8d95d0feffff         | lea                 edx, dword ptr [ebp - 0x130]

        $sequence_2 = { 85c0 7434 8d95d0feffff 52 8b45fc }
            // n = 5, score = 100
            //   85c0                 | test                eax, eax
            //   7434                 | je                  0x36
            //   8d95d0feffff         | lea                 edx, dword ptr [ebp - 0x130]
            //   52                   | push                edx
            //   8b45fc               | mov                 eax, dword ptr [ebp - 4]

        $sequence_3 = { 3945f8 7328 8b55ec 0fb702 8b4dfc 0fb711 3bc2 }
            // n = 7, score = 100
            //   3945f8               | cmp                 dword ptr [ebp - 8], eax
            //   7328                 | jae                 0x2a
            //   8b55ec               | mov                 edx, dword ptr [ebp - 0x14]
            //   0fb702               | movzx               eax, word ptr [edx]
            //   8b4dfc               | mov                 ecx, dword ptr [ebp - 4]
            //   0fb711               | movzx               edx, word ptr [ecx]
            //   3bc2                 | cmp                 eax, edx

        $sequence_4 = { 0f8394000000 8b4df0 0fb711 8b45fc 0fb708 3bd1 7576 }
            // n = 7, score = 100
            //   0f8394000000         | jae                 0x9a
            //   8b4df0               | mov                 ecx, dword ptr [ebp - 0x10]
            //   0fb711               | movzx               edx, word ptr [ecx]
            //   8b45fc               | mov                 eax, dword ptr [ebp - 4]
            //   0fb708               | movzx               ecx, word ptr [eax]
            //   3bd1                 | cmp                 edx, ecx
            //   7576                 | jne                 0x78

        $sequence_5 = { 8b4dfc 51 68???????? e8???????? 83c408 8945f4 6a00 }
            // n = 7, score = 100
            //   8b4dfc               | mov                 ecx, dword ptr [ebp - 4]
            //   51                   | push                ecx
            //   68????????           |                     
            //   e8????????           |                     
            //   83c408               | add                 esp, 8
            //   8945f4               | mov                 dword ptr [ebp - 0xc], eax
            //   6a00                 | push                0

        $sequence_6 = { 8b450c 8945f8 c745fc00220400 8b4dfc 51 68???????? e8???????? }
            // n = 7, score = 100
            //   8b450c               | mov                 eax, dword ptr [ebp + 0xc]
            //   8945f8               | mov                 dword ptr [ebp - 8], eax
            //   c745fc00220400       | mov                 dword ptr [ebp - 4], 0x42200
            //   8b4dfc               | mov                 ecx, dword ptr [ebp - 4]
            //   51                   | push                ecx
            //   68????????           |                     
            //   e8????????           |                     

        $sequence_7 = { 68???????? e8???????? 83c408 8945f4 6a00 }
            // n = 5, score = 100
            //   68????????           |                     
            //   e8????????           |                     
            //   83c408               | add                 esp, 8
            //   8945f4               | mov                 dword ptr [ebp - 0xc], eax
            //   6a00                 | push                0

        $sequence_8 = { 8bec 81ec30010000 c745f800000000 c785d0feffff28010000 6a00 }
            // n = 5, score = 100
            //   8bec                 | mov                 ebp, esp
            //   81ec30010000         | sub                 esp, 0x130
            //   c745f800000000       | mov                 dword ptr [ebp - 8], 0
            //   c785d0feffff28010000     | mov    dword ptr [ebp - 0x130], 0x128
            //   6a00                 | push                0

        $sequence_9 = { 83ec18 c745f400000000 c745f800000000 c745e800000000 8b4508 8945f0 8b4d0c }
            // n = 7, score = 100
            //   83ec18               | sub                 esp, 0x18
            //   c745f400000000       | mov                 dword ptr [ebp - 0xc], 0
            //   c745f800000000       | mov                 dword ptr [ebp - 8], 0
            //   c745e800000000       | mov                 dword ptr [ebp - 0x18], 0
            //   8b4508               | mov                 eax, dword ptr [ebp + 8]
            //   8945f0               | mov                 dword ptr [ebp - 0x10], eax
            //   8b4d0c               | mov                 ecx, dword ptr [ebp + 0xc]

    condition:
        7 of them and filesize < 582656
}
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