Cisco Cloud Security - Rare User Agent Detected

Status: available
Severity: medium
Time window: 14d
Source: github.com/Azure/Azure-Sentinel

'Rule helps to detect a rare user-agents indicating web browsing activity by an unusual process other than a web browser.'

MITRE ATT&CK coverage

Tactic	Techniques
Command & Control	`T1071.001` Application Layer Protocol: Web Protocols
Exfiltration	`T1041` Exfiltration Over C2 Channel

Rule body

id: 8c8de3fa-6425-4623-9cd9-45de1dd0569a
name: Cisco Cloud Security - Rare User Agent Detected
description: |
  'Rule helps to detect a rare user-agents indicating web browsing activity by an unusual process other than a web browser.'
severity: Medium
status: Available
requiredDataConnectors:
  - connectorId: CiscoUmbrellaDataConnector
    dataTypes:
      - Cisco_Umbrella_proxy_CL
queryFrequency: 1d
queryPeriod: 14d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - CommandAndControl
  - Exfiltration
relevantTechniques:
  - T1071.001
  - T1041
query: |
  let user_agents_list = Cisco_Umbrella
  | where EventType == "proxylogs"
  | summarize count() by HttpUserAgentOriginal
  | summarize make_list(HttpUserAgentOriginal);
  Cisco_Umbrella
  | where EventType == "proxylogs"
  | where HttpUserAgentOriginal !in (user_agents_list)
  | extend Message = "Rare User Agent"
  | project TimeGenerated, Message, SrcIpAddr, DstIpAddr, UrlOriginal, HttpUserAgentOriginal
entityMappings:
  - entityType: URL
    fieldMappings:
      - identifier: Url
        columnName: UrlOriginal
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: SrcIpAddr
version: 1.1.3
kind: Scheduled

Stages and Predicates

Let binding: `user_agents_list` used in Stage 3

let user_agents_list = Cisco_Umbrella
| where EventType == "proxylogs"
| summarize count() by HttpUserAgentOriginal
| summarize make_list(HttpUserAgentOriginal);

Stage 1: `source`

Cisco_Umbrella

Stage 2: `where`

| where EventType == "proxylogs"

Stage 3: `where`

| where HttpUserAgentOriginal !in (user_agents_list)

Stage 4: `extend`

| extend Message = "Rare User Agent"

Stage 5: `project`

| project TimeGenerated, Message, SrcIpAddr, DstIpAddr, UrlOriginal, HttpUserAgentOriginal

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`HttpUserAgentOriginal`	eq	`user_agents_list`	`excludes:HttpUserAgentOriginal` `field:"HttpUserAgentOriginal" value:"user_agents_list"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`EventType`	eq	`proxylogs`	`field:"EventType" kind:eq value:"proxylogs"`

Output fields

These fields are emitted when the rule matches.

Field	Source
`DstIpAddr`	`project`
`HttpUserAgentOriginal`	`project`
`Message`	`project`
`SrcIpAddr`	`project`
`TimeGenerated`	`project`
`UrlOriginal`	`project`

Cisco Cloud Security - Rare User Agent Detected

MITRE ATT&CK coverage

Rule body

Stages and Predicates

Let binding: user_agents_list used in Stage 3

Stage 1: source

Stage 2: where

Stage 3: where

Stage 4: extend

Stage 5: project