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 (20221125 | Detects win.nimrev.)
rule win_nimrev_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2022-11-21"
        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 = "20221118"
        malpedia_hash = "e0702e2e6d1d00da65c8a29a4ebacd0a4c59e1af"
        malpedia_version = "20221125"
        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, [0x23995]
            //   90                   | dec                 eax
            //   e9????????           |                     
            //   90                   | mov                 dword ptr [eax], 8

        $sequence_1 = { 0fb6c0 83e007 89c1 d3ea 89d0 83e001 }
            // n = 6, score = 200
            //   0fb6c0               | call                eax
            //   83e007               | dec                 eax
            //   89c1                 | mov                 dword ptr [ebp - 8], eax
            //   d3ea                 | dec                 eax
            //   89d0                 | mov                 dword ptr [ebp - 0x20], 0x102
            //   83e001               | mov                 ecx, 0

        $sequence_2 = { c1e002 01d0 01c0 29c1 89c8 83c030 89c1 }
            // n = 7, score = 200
            //   c1e002               | lea                 eax, [ebp - 0x30]
            //   01d0                 | dec                 eax
            //   01c0                 | mov                 ecx, eax
            //   29c1                 | dec                 eax
            //   89c8                 | mov                 dword ptr [ebp - 8], 0
            //   83c030               | dec                 eax
            //   89c1                 | mov                 dword ptr [ebp - 0x20], 0x81

        $sequence_3 = { 3c39 7707 b801000000 eb05 }
            // n = 4, score = 200
            //   3c39                 | jne                 0xcf
            //   7707                 | mov                 dword ptr [ebp - 0x18], 0x30
            //   b801000000           | mov                 dword ptr [ebp - 0x14], 0x422aa4
            //   eb05                 | cmp                 edx, eax

        $sequence_4 = { 7408 90 e8???????? eb01 }
            // n = 4, score = 200
            //   7408                 | dec                 eax
            //   90                   | lea                 eax, [0x18c9a]
            //   e8????????           |                     
            //   eb01                 | dec                 eax

        $sequence_5 = { 7407 e8???????? eb01 90 }
            // n = 4, score = 200
            //   7407                 | mov                 edx, dword ptr [ebp - 8]
            //   e8????????           |                     
            //   eb01                 | dec                 eax
            //   90                   | mov                 eax, edx

        $sequence_6 = { 0f97c0 8845ef eb01 90 }
            // n = 4, score = 200
            //   0f97c0               | mov                 dword ptr [ebp - 0x50], 0x5d
            //   8845ef               | dec                 eax
            //   eb01                 | lea                 eax, [0x907b]
            //   90                   | dec                 eax

        $sequence_7 = { eb05 b800000000 8845f7 eb01 90 }
            // n = 5, score = 200
            //   eb05                 | mov                 eax, dword ptr [ebp - 0xbc]
            //   b800000000           | mov                 dword ptr [esp], eax
            //   8845f7               | jmp                 0x14fd
            //   eb01                 | nop                 
            //   90                   | mov                 eax, dword ptr [ebp - 0xbc]

        $sequence_8 = { e8???????? eb01 90 e8???????? 90 }
            // n = 5, score = 200
            //   e8????????           |                     
            //   eb01                 | mov                 dword ptr [eax], edx
            //   90                   | mov                 edx, dword ptr [ebp - 0xc]
            //   e8????????           |                     
            //   90                   | mov                 eax, dword ptr [ebp - 0x10]

        $sequence_9 = { 0fb700 98 89c1 e8???????? }
            // n = 4, score = 200
            //   0fb700               | mov                 edx, dword ptr [ebp - 0x18]
            //   98                   | movzx               ecx, byte ptr [ebp - 0x34]
            //   89c1                 | mov                 edx, dword ptr [ebp - 0x14]
            //   e8????????           |                     

    condition:
        7 of them and filesize < 1141760
}
Download all Yara Rules