Malicious Inbox Rule

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Id	7b907bf7-77d4-41d0-a208-5643ff75bf9a
Rulename	Malicious Inbox Rule
Description	Often times after the initial compromise the attackers create inbox rules to delete emails that contain certain keywords. This is done so as to limit ability to warn compromised users that they’ve been compromised. Below is a sample query that tries to detect this. Reference: https://www.reddit.com/r/sysadmin/comments/7kyp0a/recent_phishing_attempts_my_experience_and_what/
Severity	Medium
Tactics	Persistence DefenseEvasion
Techniques	T1098 T1078
Required data connectors	Office365
Kind	Scheduled
Query frequency	1d
Query period	1d
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Microsoft 365/Analytic Rules/Malicious_Inbox_Rule.yaml
Version	2.0.4
Arm template	7b907bf7-77d4-41d0-a208-5643ff75bf9a.json

KQL

let Keywords = dynamic(["helpdesk", " alert", " suspicious", "fake", "malicious", "phishing", "spam", "do not click", "do not open", "hijacked", "Fatal"]);
OfficeActivity
| where OfficeWorkload =~ "Exchange" 
| where Operation =~ "New-InboxRule" and (ResultStatus =~ "True" or ResultStatus =~ "Succeeded")
| where Parameters has "Deleted Items" or Parameters has "Junk Email"  or Parameters has "DeleteMessage"
| extend Events=todynamic(Parameters)
| parse Events  with * "SubjectContainsWords" SubjectContainsWords '}'*
| parse Events  with * "BodyContainsWords" BodyContainsWords '}'*
| parse Events  with * "SubjectOrBodyContainsWords" SubjectOrBodyContainsWords '}'*
| where SubjectContainsWords has_any (Keywords)
 or BodyContainsWords has_any (Keywords)
 or SubjectOrBodyContainsWords has_any (Keywords)
| extend ClientIPAddress = case( ClientIP has ".", tostring(split(ClientIP,":")[0]), ClientIP has "[", tostring(trim_start(@'[[]',tostring(split(ClientIP,"]")[0]))), ClientIP )
| extend Keyword = iff(isnotempty(SubjectContainsWords), SubjectContainsWords, (iff(isnotempty(BodyContainsWords),BodyContainsWords,SubjectOrBodyContainsWords )))
| extend RuleDetail = case(OfficeObjectId contains '/' , tostring(split(OfficeObjectId, '/')[-1]) , tostring(split(OfficeObjectId, '\\')[-1]))
| summarize count(), StartTimeUtc = min(TimeGenerated), EndTimeUtc = max(TimeGenerated) by  Operation, UserId, ClientIPAddress, ResultStatus, Keyword, OriginatingServer, OfficeObjectId, RuleDetail
| extend AccountName = tostring(split(UserId, "@")[0]), AccountUPNSuffix = tostring(split(UserId, "@")[1])
| extend OriginatingServerName = tostring(split(OriginatingServer, " ")[0])

YAML

query: |
  let Keywords = dynamic(["helpdesk", " alert", " suspicious", "fake", "malicious", "phishing", "spam", "do not click", "do not open", "hijacked", "Fatal"]);
  OfficeActivity
  | where OfficeWorkload =~ "Exchange" 
  | where Operation =~ "New-InboxRule" and (ResultStatus =~ "True" or ResultStatus =~ "Succeeded")
  | where Parameters has "Deleted Items" or Parameters has "Junk Email"  or Parameters has "DeleteMessage"
  | extend Events=todynamic(Parameters)
  | parse Events  with * "SubjectContainsWords" SubjectContainsWords '}'*
  | parse Events  with * "BodyContainsWords" BodyContainsWords '}'*
  | parse Events  with * "SubjectOrBodyContainsWords" SubjectOrBodyContainsWords '}'*
  | where SubjectContainsWords has_any (Keywords)
   or BodyContainsWords has_any (Keywords)
   or SubjectOrBodyContainsWords has_any (Keywords)
  | extend ClientIPAddress = case( ClientIP has ".", tostring(split(ClientIP,":")[0]), ClientIP has "[", tostring(trim_start(@'[[]',tostring(split(ClientIP,"]")[0]))), ClientIP )
  | extend Keyword = iff(isnotempty(SubjectContainsWords), SubjectContainsWords, (iff(isnotempty(BodyContainsWords),BodyContainsWords,SubjectOrBodyContainsWords )))
  | extend RuleDetail = case(OfficeObjectId contains '/' , tostring(split(OfficeObjectId, '/')[-1]) , tostring(split(OfficeObjectId, '\\')[-1]))
  | summarize count(), StartTimeUtc = min(TimeGenerated), EndTimeUtc = max(TimeGenerated) by  Operation, UserId, ClientIPAddress, ResultStatus, Keyword, OriginatingServer, OfficeObjectId, RuleDetail
  | extend AccountName = tostring(split(UserId, "@")[0]), AccountUPNSuffix = tostring(split(UserId, "@")[1])
  | extend OriginatingServerName = tostring(split(OriginatingServer, " ")[0])  
triggerThreshold: 0
status: Available
version: 2.0.4
requiredDataConnectors:
- dataTypes:
  - OfficeActivity (Exchange)
  connectorId: Office365
relevantTechniques:
- T1098
- T1078
queryFrequency: 1d
triggerOperator: gt
kind: Scheduled
entityMappings:
- entityType: Account
  fieldMappings:
  - identifier: FullName
    columnName: UserId
  - identifier: Name
    columnName: AccountName
  - identifier: UPNSuffix
    columnName: AccountUPNSuffix
- entityType: Host
  fieldMappings:
  - identifier: FullName
    columnName: OriginatingServerName
- entityType: IP
  fieldMappings:
  - identifier: Address
    columnName: ClientIPAddress
description: |
  'Often times after the initial compromise the attackers create inbox rules to delete emails that contain certain keywords.
   This is done so as to limit ability to warn compromised users that they've been compromised. Below is a sample query that tries to detect this.
  Reference: https://www.reddit.com/r/sysadmin/comments/7kyp0a/recent_phishing_attempts_my_experience_and_what/'  
severity: Medium
tactics:
- Persistence
- DefenseEvasion
name: Malicious Inbox Rule
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Microsoft 365/Analytic Rules/Malicious_Inbox_Rule.yaml
id: 7b907bf7-77d4-41d0-a208-5643ff75bf9a
queryPeriod: 1d

ARM