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Detection rules › Kusto

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

TacticTechniques
Command & ControlT1071.001 Application Layer Protocol: Web Protocols

Rule body kusto

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

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

Derived from lbperiod.

Stage 1: source

SlackAudit

Stage 2: where

| where UserAgentOriginal !in (known_UAs)

References known_UAs (defined above).

Stage 3: extend

| extend AccountCustomEntity = SrcUserName

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

FieldKindExcluded values
UserAgentOriginaleqknown_UAs

Output fields

Fields the rule emits when it matches. Chronicle authors list these in the outcome block; they appear on the detection and $risk_score drives alerting. Sentinel / Defender XDR rules build them up through project / summarize / extend stages. Sentinel maps these into alert fields via entityMappings and customDetails; Defender XDR custom detections surface them as alert fields directly.

FieldSource
AccountCustomEntityextend