O365 Cross-Tenant Access Change

Status: production
Severity: medium
Group by: aws::recipientAccountId, dest, signature, signature_id, src, user, vendor_product
Author: Steven Dick
Source: github.com/splunk/security_content

The following analytic identifies when cross-tenant access/synchronization policies are changed in an Azure tenant. Adversaries have been observed altering victim cross-tenant policies as a method of lateral movement or maintaining persistent access to compromised environments. These policies should be considered sensitive and monitored for changes and/or loose configuration.

MITRE ATT&CK coverage

Tactic	Techniques
Privilege Escalation	`T1484.002` Domain or Tenant Policy Modification: Trust Modification
Defense Impairment	`T1484.002` Domain or Tenant Policy Modification: Trust Modification

Rule body splunk

name: O365 Cross-Tenant Access Change
id: 7c0fa490-12b0-4d0b-b9f5-e101d1e0e06f
version: 9
creation_date: '2024-04-13'
modification_date: '2026-05-13'
author: Steven Dick
status: production
type: TTP
description: The following analytic identifies when cross-tenant access/synchronization policies are changed in an Azure tenant. Adversaries have been observed altering victim cross-tenant policies as a method of lateral movement or maintaining persistent access to compromised environments. These policies should be considered sensitive and monitored for changes and/or loose configuration.
data_source:
    - Office 365 Universal Audit Log
search: "`o365_management_activity` Workload=AzureActiveDirectory Operation IN (\"Add a partner to cross-tenant access setting.\",\"Delete partner specific cross-tenant access setting.\") | eval user = case(match(mvindex('Actor{}.ID',-1),\"User\"),mvindex('Actor{}.ID',0),match(mvindex('Actor{}.ID',-1),\"ServicePrincipal\"),mvindex('Actor{}.ID',3),true(),mvindex('Actor{}.ID',0)) | fillnull | stats count min(_time) as firstTime max(_time) as lastTime by dest user src vendor_account vendor_product signature signature_id | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `o365_cross_tenant_access_change_filter`"
how_to_implement: You must install the Splunk Microsoft Office 365 Add-on and ingest Office 365 management activity events.
known_false_positives: Business approved changes by known administrators.
references:
    - https://attack.mitre.org/techniques/T1484/002/
    - https://thehackernews.com/2023/08/emerging-attacker-exploit-microsoft.html
    - https://cyberaffairs.com/news/emerging-attacker-exploit-microsoft-cross-tenant-synchronization/
    - https://www.crowdstrike.com/blog/crowdstrike-defends-against-azure-cross-tenant-synchronization-attacks/
drilldown_searches:
    - name: View the detection results for - "$user$"
      search: '%original_detection_search% | search  user = "$user$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$user$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: 7d
      latest_offset: "0"
finding:
    title: The user [$user$] changed the Azure cross-tenant access settings
    entity:
        field: user
        type: user
        score: 50
analytic_story:
    - Azure Active Directory Persistence
asset_type: O365 Tenant
mitre_attack_id:
    - T1484.002
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: cloud
security_domain: threat
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1098/o365_azure_workload_events/o365_azure_workload_events.log
          sourcetype: o365:management:activity
          source: o365
      test_type: unit

Stages and Predicates

Stage 1: `search`

`o365_management_activity` Workload=AzureActiveDirectory Operation IN ("Add a partner to cross-tenant access setting.","Delete partner specific cross-tenant access setting.")

Stage 2: `eval`

| eval user = case(match(mvindex('Actor{}.ID',-1),"User"),mvindex('Actor{}.ID',0),match(mvindex('Actor{}.ID',-1),"ServicePrincipal"),mvindex('Actor{}.ID',3),true(),mvindex('Actor{}.ID',0))

user =

ifmatch(mvindex('Actor{}.ID', -1), "User")mvindex('Actor{}.ID', 0)

elifmatch(mvindex('Actor{}.ID', -1), "ServicePrincipal")mvindex('Actor{}.ID', 3)

elsemvindex('Actor{}.ID', 0)

Stage 3: `fillnull`

| fillnull

Stage 4: `stats`

| stats count min(_time) as firstTime max(_time) as lastTime by dest user src vendor_account vendor_product signature signature_id

Stage 5: `search`

| `security_content_ctime(firstTime)`

Stage 6: `search`

| `security_content_ctime(lastTime)`

Stage 7: `search`

| `o365_cross_tenant_access_change_filter`

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`Operation`	in	`"Add a partner to cross-tenant access setting."` `"Delete partner specific cross-tenant access setting."`
`Workload`	eq	`AzureActiveDirectory`
`sourcetype`	eq	`o365:management:activity`

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

O365 Cross-Tenant Access Change

MITRE ATT&CK coverage

Rule body splunk

Stages and Predicates

Stage 1: `search`

Stage 2: `eval`

Stage 3: `fillnull`

Stage 4: `stats`

Stage 5: `search`

Stage 6: `search`

Stage 7: `search`

Indicators

Keyboard shortcuts

Search operators

O365 Cross-Tenant Access Change

MITRE ATT&CK coverage

Rule body splunk

Stages and Predicates

Stage 1: search

Stage 2: eval

Stage 3: fillnull

Stage 4: stats

Stage 5: search

Stage 6: search

Stage 7: search

Indicators

Stage 1: `search`

Stage 2: `eval`

Stage 3: `fillnull`

Stage 4: `stats`

Stage 5: `search`

Stage 6: `search`

Stage 7: `search`