DNS TXT Answer with possible execution strings

Detects strings used in command execution in DNS TXT Answer

Rule Content

- title: DNS TXT Answer with possible execution strings
  id: 8ae51330-899c-4641-8125-e39f2e07da72
  status: experimental
  description: Detects strings used in command execution in DNS TXT Answer
  references:
  - https://twitter.com/stvemillertime/status/1024707932447854592
  - https://github.com/samratashok/nishang/blob/master/Backdoors/DNS_TXT_Pwnage.ps1
  tags:
  - attack.t1071
  author: Markus Neis
  date: 2018/08/08
  logsource:
    category: dns
    product: null
    service: null
  detection:
    selection:
      record_type: TXT
      answer:
      - '*IEX*'
      - '*Invoke-Expression*'
      - '*cmd.exe*'
    condition: selection
  falsepositives:
  - Unknown
  level: high

Querying Elasticsearch

Import Libraries



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from elasticsearch import Elasticsearch
from elasticsearch_dsl import Search
import pandas as pd

Initialize Elasticsearch client



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es = Elasticsearch(['http://helk-elasticsearch:9200'])
searchContext = Search(using=es, index='logs-*', doc_type='doc')

Run Elasticsearch Query



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s = searchContext.query('query_string', query='(record_type:"TXT" AND answer.keyword:(*IEX* OR *Invoke\-Expression* OR *cmd.exe*))')
response = s.execute()
if response.success():
    df = pd.DataFrame((d.to_dict() for d in s.scan()))

Show Results



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df.head()