NRT Malicious Inbox Rule

Severity: medium
Group by: ClientIPAddress, Keyword, OfficeObjectId, OriginatingServer, ResultStatus, RuleDetail, UserId
Author: Pete Bryan
Source: github.com/Azure/Azure-Sentinel

'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/'

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1078` Valid Accounts `T1098` Account Manipulation
Stealth	`T1078` Valid Accounts

Rules detecting the same action

These rules filter on the same operation.

Rule body

id: b79f6190-d104-4691-b7db-823e05980895
name: NRT 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
requiredDataConnectors:
  - connectorId: Office365
    dataTypes:
      - OfficeActivity
tactics:
  - Persistence
  - DefenseEvasion
relevantTechniques:
  - T1098
  - T1078
query: |
 let Keywords = dynamic(["helpdesk", " alert", " suspicious", "fake", "malicious", "phishing", "spam", "do not click", "do not open", "hijacked", "Fatal"]);
 OfficeActivity
 | where OfficeWorkload =~ "Exchange"
 | 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  UserId, ClientIPAddress, ResultStatus, Keyword, OriginatingServer, OfficeObjectId, RuleDetail
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: UserId
  - entityType: Host
    fieldMappings:
      - identifier: FullName
        columnName: OriginatingServer
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: ClientIPAddress
version: 1.0.2
kind: NRT
metadata:
    source:
        kind: Community
    author:
        name: Pete Bryan
    support:
        tier: Community
    categories:
        domains: [ "Security - Threat Protection" ]

Stages and Predicates

Parameters

let Keywords = dynamic(["helpdesk", " alert", " suspicious", "fake", "malicious", "phishing", "spam", "do not click", "do not open", "hijacked", "Fatal"]);

Stage 1: `source`

OfficeActivity

Stage 2: `where`

| where OfficeWorkload =~ "Exchange"

Stage 3: `where`

| where Parameters has "Deleted Items" or Parameters has "Junk Email"  or Parameters has "DeleteMessage"

Stage 4: `extend`

| extend Events=todynamic(Parameters)

Stage 5: `parse`

| parse Events  with * "SubjectContainsWords" SubjectContainsWords '}'*

Stage 6: `parse`

| parse Events  with * "BodyContainsWords" BodyContainsWords '}'*

Stage 7: `parse`

| parse Events  with * "SubjectOrBodyContainsWords" SubjectOrBodyContainsWords '}'*

Stage 8: `where`

| where SubjectContainsWords has_any (Keywords)
 or BodyContainsWords has_any (Keywords)
 or SubjectOrBodyContainsWords has_any (Keywords)

Stage 9: `extend` (3 consecutive steps)

| 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]))

ClientIPAddress =

ifClientIP has "."tostring(split(ClientIP, ":")[0])

elifClientIP has "["tostring(trim_start(@'[[]', tostring(split(ClientIP, "]")[0])))

elseClientIP

Stage 10: `summarize`

| summarize count(), StartTimeUtc = min(TimeGenerated), EndTimeUtc = max(TimeGenerated) by  UserId, ClientIPAddress, ResultStatus, Keyword, OriginatingServer, OfficeObjectId, RuleDetail

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`BodyContainsWords`	match	`alert` transforms: `term` `suspicious` transforms: `term` `Fatal` transforms: `term` `do not click` transforms: `term` `do not open` transforms: `term` `fake` transforms: `term` `helpdesk` transforms: `term` `hijacked` transforms: `term` `malicious` transforms: `term` `phishing` transforms: `term` `spam` transforms: `term`	`field:"BodyContainsWords" kind:match`
`OfficeWorkload`	eq	`Exchange`	`field:"m365::Workload" kind:eq value:"Exchange"`
`Parameters`	match	`DeleteMessage` transforms: `term` `Deleted Items` transforms: `term` `Junk Email` transforms: `term`	`field:"m365::Parameters" kind:match`
`SubjectContainsWords`	match	`alert` transforms: `term` `suspicious` transforms: `term` `Fatal` transforms: `term` `do not click` transforms: `term` `do not open` transforms: `term` `fake` transforms: `term` `helpdesk` transforms: `term` `hijacked` transforms: `term` `malicious` transforms: `term` `phishing` transforms: `term` `spam` transforms: `term`	`field:"SubjectContainsWords" kind:match`
`SubjectOrBodyContainsWords`	match	`alert` transforms: `term` `suspicious` transforms: `term` `Fatal` transforms: `term` `do not click` transforms: `term` `do not open` transforms: `term` `fake` transforms: `term` `helpdesk` transforms: `term` `hijacked` transforms: `term` `malicious` transforms: `term` `phishing` transforms: `term` `spam` transforms: `term`	`field:"SubjectOrBodyContainsWords" kind:match`

Output fields

These fields are emitted when the rule matches.

Field	Source
`ClientIPAddress`	`summarize`
`EndTimeUtc`	`summarize`
`Keyword`	`summarize`
`OfficeObjectId`	`summarize`
`OriginatingServer`	`summarize`
`ResultStatus`	`summarize`
`RuleDetail`	`summarize`
`StartTimeUtc`	`summarize`
`UserId`	`summarize`

NRT Malicious Inbox Rule

MITRE ATT&CK coverage

Rules detecting the same action

Rule body

Stages and Predicates

Parameters

Stage 1: source

Stage 2: where

Stage 3: where

Stage 4: extend

Stage 5: parse

Stage 6: parse

Stage 7: parse

Stage 8: where

Stage 9: extend (3 consecutive steps)

Stage 10: summarize