Remote Desktop Network Brute force (ASIM Network Session schema)

Status: available
Severity: medium
Time window: 5m
Group by: DstPortNumber, EventResult, SrcIpAddr
Source: github.com/Azure/Azure-Sentinel

This detection identifies RDP application network traffic and filters any source/destination pair generating more than 25 events hard threshold.

MITRE ATT&CK coverage

Tactic	Techniques
Credential Access	`T1110` Brute Force

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 3: Network connection
Security-Auditing	Event ID 5152: The Windows Filtering Platform blocked a packet.
Security-Auditing	Event ID 5154: The Windows Filtering Platform has permitted an application or service to listen on a port for incoming connections.
Security-Auditing	Event ID 5155: The Windows Filtering Platform has blocked an application or service from listening on a port for incoming connections.
Security-Auditing	Event ID 5156: The Windows Filtering Platform has permitted a connection.
Security-Auditing	Event ID 5157: The Windows Filtering Platform has blocked a connection.
Security-Auditing	Event ID 5158: The Windows Filtering Platform has permitted a bind to a local port.
Security-Auditing	Event ID 5159: The Windows Filtering Platform has blocked a bind to a local port.

Rule body

id: b7dc801e-1e79-48bb-91e8-2229a8e6d40b
name: Remote Desktop Network Brute force (ASIM Network Session schema)
description: |
  'This detection identifies RDP application network traffic and filters any source/destination pair generating more than 25 events hard threshold.'
severity: Medium
status: Available 
tags:
  - Schema: ASimNetworkSessions
    SchemaVersion: 0.2.4
requiredDataConnectors: []
queryFrequency: 1h
queryPeriod: 1h
triggerOperator: gt
triggerThreshold: 0
tactics:
  - CredentialAccess
relevantTechniques:
  - T1110
query: |
  // Start of the query and  Filter events that resulted in failure
  _Im_NetworkSession(eventresult="Failure")
  // Filter out private source IP addresses and focus on specific destination port (3389)
  // Also, ensure that the source and destination IP addresses are not the same
  | where not(ipv4_is_private(SrcIpAddr)) and tostring(DstPortNumber) has_any ("3389") and SrcIpAddr != DstIpAddr
  // Summarize the data by source and destination IP addresses, destination port number, network protocol, and event result
  // Also, bin the time generated in 5-minute intervals
  // Calculate the minimum and maximum time generated, the sum of event counts, and a set of up to 10 event vendors
  | summarize Starttime= min(TimeGenerated),EndTime= max(TimeGenerated),TargettedIPs=dcount(DstIpAddr),Eventscount=sum(EventCount),EventVendors=make_set(EventVendor,10) by SrcIpAddr,DstPortNumber,EventResult, bin(TimeGenerated, 5m)
  // Filter the summarized data to include only those with an event count of 25 or more
  | where Eventscount >= 25
entityMappings:
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: SrcIpAddr
eventGroupingSettings:
  aggregationKind: AlertPerResult
version: 1.0.0
kind: Scheduled

Stages and Predicates

Stage 1: `source`

_Im_NetworkSession(eventresult="Failure")

Stage 2: `where`

| where not(ipv4_is_private(SrcIpAddr)) and tostring(DstPortNumber) has_any ("3389") and SrcIpAddr != DstIpAddr

Stage 3: `summarize`

| summarize Starttime= min(TimeGenerated),EndTime= max(TimeGenerated),TargettedIPs=dcount(DstIpAddr),Eventscount=sum(EventCount),EventVendors=make_set(EventVendor,10) by SrcIpAddr,DstPortNumber,EventResult, bin(TimeGenerated, 5m)

Stage 4: `where`

| where Eventscount >= 25

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`SrcIpAddr`	cidr_match	`10.0.0.0/8`, `172.16.0.0/12`, `192.168.0.0/16`, `169.254.0.0/16`, `127.0.0.0/8`	`excludes:SrcIpAddr`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`DstPortNumber`	match	`3389` transforms: `tostring`, `term`	`field:"DstPortNumber" kind:match value:"3389"`
`Eventscount`	ge	`25`	`field:"Eventscount" kind:ge value:"25"`
`SrcIpAddr`	cross_field_compare	`DstIpAddr` transforms: `op:ne` corpus 2 (kusto 2)	`field:"src_ip" kind:cross_field_compare value:"DstIpAddr"`

Output fields

These fields are emitted when the rule matches.

Field	Source
`DstPortNumber`	`summarize`
`EndTime`	`summarize`
`EventResult`	`summarize`
`EventVendors`	`summarize`
`Eventscount`	`summarize`
`SrcIpAddr`	`summarize`
`Starttime`	`summarize`
`TargettedIPs`	`summarize`