SYMBOLCOMMON_NAMEaka. SYNONYMS
win.nimrev (Back to overview)

Nimrev


Backdoor written in Nim.

References
2021-10-14Medium walmartglobaltechJason Reaves
@online{reaves:20211014:investigation:29ef29c, author = {Jason Reaves}, title = {{Investigation into the state of NIM malware Part 2}}, date = {2021-10-14}, organization = {Medium walmartglobaltech}, url = {https://medium.com/walmartglobaltech/investigation-into-the-state-of-nim-malware-part-2-a28bffffa671}, language = {English}, urldate = {2021-12-15} } Investigation into the state of NIM malware Part 2
Cobalt Strike NimGrabber Nimrev Unidentified 088 (Nim Ransomware)
Yara Rules
[TLP:WHITE] win_nimrev_auto (20220516 | Detects win.nimrev.)
rule win_nimrev_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2022-05-16"
        version = "1"
        description = "Detects win.nimrev."
        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.nimrev"
        malpedia_rule_date = "20220513"
        malpedia_hash = "7f4b2229e6ae614d86d74917f6d5b41890e62a26"
        malpedia_version = "20220516"
        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 = { 66c700fdff 90 e9???????? 90 }
            // n = 4, score = 200
            //   66c700fdff           | lea                 eax, [0x268ec]
            //   90                   | dec                 eax
            //   e9????????           |                     
            //   90                   | mov                 dword ptr [ebp - 0x28], eax

        $sequence_1 = { 89c1 e8???????? eb04 90 eb01 90 }
            // n = 6, score = 200
            //   89c1                 | dec                 eax
            //   e8????????           |                     
            //   eb04                 | mov                 ecx, eax
            //   90                   | dec                 eax
            //   eb01                 | lea                 eax, [0x25ee0]
            //   90                   | dec                 eax

        $sequence_2 = { 0fb600 3c5f 7507 b801000000 eb05 }
            // n = 5, score = 200
            //   0fb600               | mov                 dword ptr [esp], eax
            //   3c5f                 | mov                 dword ptr [ebp - 0x14], 0
            //   7507                 | mov                 eax, dword ptr [ebp - 0x3c]
            //   b801000000           | mov                 eax, dword ptr [eax + 4]
            //   eb05                 | add                 eax, 1

        $sequence_3 = { 0fb600 3c39 7707 b801000000 eb05 }
            // n = 5, score = 200
            //   0fb600               | mov                 dword ptr [ebp - 0xc], 0
            //   3c39                 | nop                 
            //   7707                 | mov                 dword ptr [ebp - 0x18], 0xfa
            //   b801000000           | mov                 dword ptr [ebp - 0x14], 0x422a78
            //   eb05                 | mov                 eax, dword ptr [ebp - 0x2c]

        $sequence_4 = { 90 e9???????? 90 b9d0070000 }
            // n = 4, score = 200
            //   90                   | mov                 dword ptr [ebp - 0x70], 0xb8
            //   e9????????           |                     
            //   90                   | mov                 ecx, eax
            //   b9d0070000           | dec                 eax

        $sequence_5 = { 90 e9???????? 90 eb01 }
            // n = 4, score = 200
            //   90                   | mov                 dword ptr [ebp - 0x28], eax
            //   e9????????           |                     
            //   90                   | mov                 dword ptr [esp + 4], 2
            //   eb01                 | mov                 ecx, eax

        $sequence_6 = { 90 eb01 90 e8???????? 90 }
            // n = 5, score = 200
            //   90                   | mov                 dword ptr [esp], eax
            //   eb01                 | mov                 dword ptr [ebp - 0x14], 0x6a1
            //   90                   | mov                 dword ptr [ebp - 0x10], 0x423a08
            //   e8????????           |                     
            //   90                   | mov                 ebx, dword ptr [ebp - 0x2c]

        $sequence_7 = { 0f97c0 8845ef eb01 90 807def00 }
            // n = 5, score = 200
            //   0f97c0               | mov                 eax, dword ptr [eax]
            //   8845ef               | mov                 dword ptr [ebp - 0x18], 0x379
            //   eb01                 | mov                 dword ptr [ebp - 0x14], 0x4244a9
            //   90                   | mov                 eax, dword ptr [ebp - 0x2c]
            //   807def00             | mov                 ecx, eax

        $sequence_8 = { e8???????? e8???????? eb04 90 }
            // n = 4, score = 200
            //   e8????????           |                     
            //   e8????????           |                     
            //   eb04                 | mov                 dword ptr [esp + 0xc], 0
            //   90                   | mov                 eax, dword ptr [ebp - 0x10]

        $sequence_9 = { d3ea 89d0 83e001 85c0 }
            // n = 4, score = 200
            //   d3ea                 | add                 eax, edx
            //   89d0                 | mov                 ecx, eax
            //   83e001               | mov                 eax, 0
            //   85c0                 | sub                 eax, dword ptr [ebp - 0x44]

    condition:
        7 of them and filesize < 1141760
}
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