Potential DGA detected (ASIM DNS Schema)

Hunt Hypothesis

‘Identifies clients with a high NXDomain count which could be indicative of a DGA (cycling through possible C2 domains where most C2s are not live). Alert is generated when a new IP address is seen (b

KQL Query

let referencestarttime = 10d;
let referenceendtime = 1d;
let threshold = 100;
let nxDomainDnsEvents = (stime:datetime, etime:datetime) 
  {_Im_Dns(responsecodename='NXDOMAIN', starttime=stime, endtime=etime)
  | where DnsQueryTypeName in ("A", "AAAA")
  | where ipv4_is_match("127.0.0.1", SrcIpAddr) == False
  | where DnsQuery !contains "/" and  DnsQuery contains "."};
nxDomainDnsEvents (stime=ago(referenceendtime) ,etime=now())
  | extend sld = tostring(split(DnsQuery, ".")[-2])
  | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), dcount(sld) by SrcIpAddr
  | where dcount_sld > threshold
  // Filter out previously seen IPs
  | join kind=leftanti (nxDomainDnsEvents (stime=ago(referencestarttime), etime=ago(referenceendtime))
    | extend sld = tostring(split(DnsQuery, ".")[-2])
    | summarize dcount(sld) by SrcIpAddr
    | where dcount_sld > threshold ) on SrcIpAddr
// Pull out sample NXDomain responses for those remaining potentially infected IPs
| join kind = inner (nxDomainDnsEvents (stime=ago(referencestarttime), etime=now()) | summarize by DnsQuery, SrcIpAddr) on SrcIpAddr
| summarize StartTime = min(StartTime), EndTime = max(EndTime), sampleNXDomainList=make_list(DnsQuery, 100)  by SrcIpAddr, dcount_sld

Analytic Rule Definition

id: 983a6922-894d-413c-9f04-d7add0ecc307
name: Potential DGA detected (ASIM DNS Schema)
description: |
  'Identifies clients with a high NXDomain count which could be indicative of a DGA (cycling through possible C2 domains where most C2s are not live). Alert is generated when a new IP address is seen (based on not being seen associated with 
  NXDomain records in prior 10-day baseline period).
  This analytic rule uses [ASIM](https://aka.ms/AboutASIM) and supports any built-in or custom source that supports the ASIM DNS schema'
severity: Medium
requiredDataConnectors:
  - connectorId: DNS
    dataTypes:
      - DnsEvents
  - connectorId: AzureFirewall
    dataTypes: 
      - AzureDiagnostics
  - connectorId: Zscaler
    dataTypes:
      - CommonSecurityLog
  - connectorId: InfobloxNIOS
    dataTypes: 
      - Syslog
  - connectorId: GCPDNSDataConnector
    dataTypes: 
      - GCP_DNS_CL
  - connectorId: NXLogDnsLogs
    dataTypes: 
      - NXLog_DNS_Server_CL
  - connectorId: CiscoUmbrellaDataConnector
    dataTypes: 
      - Cisco_Umbrella_dns_CL
  - connectorId: Corelight
    dataTypes: 
      - Corelight_CL

queryFrequency: 1d
queryPeriod: 10d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - CommandAndControl
relevantTechniques:
  - T1568
  - T1008
tags:
  - ParentAlert: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/DnsEvents/DNS_HighNXDomainCount_detection.yaml
    version: 1.0.0
  - Schema: ASIMDns
    SchemaVersion: 0.1.1
query: |
  let referencestarttime = 10d;
  let referenceendtime = 1d;
  let threshold = 100;
  let nxDomainDnsEvents = (stime:datetime, etime:datetime) 
    {_Im_Dns(responsecodename='NXDOMAIN', starttime=stime, endtime=etime)
    | where DnsQueryTypeName in ("A", "AAAA")
    | where ipv4_is_match("127.0.0.1", SrcIpAddr) == False
    | where DnsQuery !contains "/" and  DnsQuery contains "."};
  nxDomainDnsEvents (stime=ago(referenceendtime) ,etime=now())
    | extend sld = tostring(split(DnsQuery, ".")[-2])
    | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), dcount(sld) by SrcIpAddr
    | where dcount_sld > threshold
    // Filter out previously seen IPs
    | join kind=leftanti (nxDomainDnsEvents (stime=ago(referencestarttime), etime=ago(referenceendtime))
      | extend sld = tostring(split(DnsQuery, ".")[-2])
      | summarize dcount(sld) by SrcIpAddr
      | where dcount_sld > threshold ) on SrcIpAddr
  // Pull out sample NXDomain responses for those remaining potentially infected IPs
  | join kind = inner (nxDomainDnsEvents (stime=ago(referencestarttime), etime=now()) | summarize by DnsQuery, SrcIpAddr) on SrcIpAddr
  | summarize StartTime = min(StartTime), EndTime = max(EndTime), sampleNXDomainList=make_list(DnsQuery, 100)  by SrcIpAddr, dcount_sld
entityMappings:
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: SrcIpAddr
version: 1.3.4
kind: Scheduled
metadata:
    source:
        kind: Community
    author:
        name: Yaron
    

Required Data Sources

MITRE ATT&CK Context

• Tactic: CommandAndControl
• Tactic: Command and Control
• Technique: T1568 — Dynamic Resolution

  Adversaries may dynamically establish connections to command and control infrastructure to evade common detections and remediations. This may be achieved by using malware that shares a common algorith

• Technique: T1008 — Fallback Channels

  Adversaries may use fallback or alternate communication channels if the primary channel is compromised or inaccessible in order to maintain reliable command and control and to avoid data transfer thre

References

• Source Query