Azure DevOps Build Variable Modified by New User

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Id	3b9a44d7-c651-45ed-816c-eae583a6f2f1
Rulename	Azure DevOps Build Variable Modified by New User
Description	Variables can be configured and used at any stage of the build process in Azure DevOps to inject values. An attacker with the required permissions could modify or add to these variables to conduct malicious activity such as changing paths or remote endpoints called during the build. As variables are often changed by users, just detecting these changes would have a high false positive rate. This detection looks for modifications to variable groups where that user has not been observed modifying them before.
Severity	Medium
Tactics	DefenseEvasion
Techniques	T1578
Kind	Scheduled
Query frequency	1d
Query period	14d
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/AzureDevOpsAuditing/Analytic Rules/ADOVariableModifiedByNewUser.yaml
Version	1.0.6
Arm template	3b9a44d7-c651-45ed-816c-eae583a6f2f1.json

KQL

let lookback = 14d;
let timeframe = 1d;
let historical_data =
ADOAuditLogs
| where TimeGenerated > ago(lookback) and TimeGenerated < ago(timeframe)
| where OperationName =~ "Library.VariableGroupModified"
| extend variables = Data.Variables
| extend VariableGroupId = tostring(Data.VariableGroupId)
| extend UserKey = strcat(VariableGroupId, "-", ActorUserId)
| project UserKey;
ADOAuditLogs
| where TimeGenerated > ago(timeframe)
| where OperationName =~ "Library.VariableGroupModified"
| extend VariableGroupName = tostring(Data.VariableGroupName)
| extend VariableGroupId = tostring(Data.VariableGroupId)
| extend UserKey = strcat(VariableGroupId, "-", ActorUserId)
| where UserKey !in (historical_data)
| project-away UserKey
| project-reorder TimeGenerated, VariableGroupName, ActorUPN, IpAddress, UserAgent
| extend timestamp = TimeGenerated
| extend AccountName = tostring(split(ActorUPN, "@")[0]), AccountUPNSuffix = tostring(split(ActorUPN, "@")[1])

YAML

description: |
  'Variables can be configured and used at any stage of the build process in Azure DevOps to inject values. An attacker with the required permissions could modify or add to these variables to conduct malicious activity such as changing paths or remote endpoints called during the build.
  As variables are often changed by users, just detecting these changes would have a high false positive rate. This detection looks for modifications to variable groups where that user has not been observed modifying them before.'  
entityMappings:
- fieldMappings:
  - columnName: ActorUPN
    identifier: FullName
  - columnName: AccountName
    identifier: Name
  - columnName: AccountUPNSuffix
    identifier: UPNSuffix
  entityType: Account
- fieldMappings:
  - columnName: IpAddress
    identifier: Address
  entityType: IP
query: |
  let lookback = 14d;
  let timeframe = 1d;
  let historical_data =
  ADOAuditLogs
  | where TimeGenerated > ago(lookback) and TimeGenerated < ago(timeframe)
  | where OperationName =~ "Library.VariableGroupModified"
  | extend variables = Data.Variables
  | extend VariableGroupId = tostring(Data.VariableGroupId)
  | extend UserKey = strcat(VariableGroupId, "-", ActorUserId)
  | project UserKey;
  ADOAuditLogs
  | where TimeGenerated > ago(timeframe)
  | where OperationName =~ "Library.VariableGroupModified"
  | extend VariableGroupName = tostring(Data.VariableGroupName)
  | extend VariableGroupId = tostring(Data.VariableGroupId)
  | extend UserKey = strcat(VariableGroupId, "-", ActorUserId)
  | where UserKey !in (historical_data)
  | project-away UserKey
  | project-reorder TimeGenerated, VariableGroupName, ActorUPN, IpAddress, UserAgent
  | extend timestamp = TimeGenerated
  | extend AccountName = tostring(split(ActorUPN, "@")[0]), AccountUPNSuffix = tostring(split(ActorUPN, "@")[1])  
tactics:
- DefenseEvasion
severity: Medium
triggerThreshold: 0
queryFrequency: 1d
status: Available
queryPeriod: 14d
relevantTechniques:
- T1578
id: 3b9a44d7-c651-45ed-816c-eae583a6f2f1
name: Azure DevOps Build Variable Modified by New User
kind: Scheduled
triggerOperator: gt
version: 1.0.6
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/AzureDevOpsAuditing/Analytic Rules/ADOVariableModifiedByNewUser.yaml
requiredDataConnectors: []

ARM