SlackAudit - Unknown User Agent

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

'Detects Slack workspace activity from unknown user agents by comparing recent UserAgentOriginal values against a 14d baseline of known user agents.'

MITRE ATT&CK coverage

Tactic	Techniques
Command & Control	`T1071.001` Application Layer Protocol: Web Protocols

Rule body

id: 3b11f06e-4afd-4ae6-8477-c61136619ac8
name: SlackAudit - Unknown User Agent
description: |
  'Detects Slack workspace activity from unknown user agents by comparing recent UserAgentOriginal values against
  a 14d baseline of known user agents.'
severity: Low
status: Available
requiredDataConnectors:
  - connectorId: SlackAuditAPI
    dataTypes:
      - SlackAudit_CL
queryFrequency: 24h
queryPeriod: 14d
triggerOperator: gt
triggerThreshold: 0
tactics: 
  - CommandAndControl
relevantTechniques:
  - T1071
  - T1071.001
query: |
  let lbperiod = 14d;
  let known_UAs = SlackAudit
  | where TimeGenerated > ago(lbperiod)
  | where isnotempty(UserAgentOriginal)
  | summarize makeset(UserAgentOriginal);
  SlackAudit
  | where UserAgentOriginal !in (known_UAs)
  | extend AccountCustomEntity = SrcUserName
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: AccountCustomEntity
alertDetailsOverride:
  alertDisplayNameFormat: Slack audit unknown user agent for {{AccountCustomEntity}}
  alertDescriptionFormat: Slack activity from {{AccountCustomEntity}} used unknown user agent {{UserAgentOriginal}}
customDetails:
  Account: AccountCustomEntity
  UserAgent: UserAgentOriginal
version: 1.0.2
kind: Scheduled

Stages and Predicates

Parameters

let lbperiod = 14d;

Let binding: `known_UAs` used in Stage 2

let known_UAs = SlackAudit
| where TimeGenerated > ago(lbperiod)
| where isnotempty(UserAgentOriginal)
| summarize makeset(UserAgentOriginal);

Stage 1: `source`

SlackAudit

Stage 2: `where`

| where UserAgentOriginal !in (known_UAs)

Stage 3: `extend`

| extend AccountCustomEntity = SrcUserName

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`UserAgentOriginal`	eq	`known_UAs`	`excludes:UserAgentOriginal` `field:"UserAgentOriginal" value:"known_UAs"`

Output fields

These fields are emitted when the rule matches.

Field	Source
`AccountCustomEntity`	`extend`