Guest Users Invited To Tenant By Non Approved Inviters

Status: test
Severity: medium
Log source: product azure, service auditlogs
Author: MikeDuddington, '@dudders1'
Source: github.com/SigmaHQ/sigma

Detects guest users being invited to tenant by non-approved inviters

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1078` Valid Accounts
Persistence	`T1078` Valid Accounts
Privilege Escalation	`T1078` Valid Accounts
Stealth	`T1078` Valid Accounts

Event coverage

Provider	Event
Entra-AuditLogs	Invite external user

Rules detecting the same action

Other rules on this platform that filter on the same API call or operation.

Authentication Method Changed for Privileged Account (Kusto)
Authentication Methods Changed for Privileged Account (Kusto)
Change to Authentication Method (Sigma)
Multi Factor Authentication Disabled For User Account (Sigma)
New External User Granted Admin Role (Kusto)
NRT Authentication Methods Changed for VIP Users (Kusto)
Password Reset By User Account (Sigma)
Suspicious Login from deleted guest account (Kusto)

Rule body yaml

title: Guest Users Invited To Tenant By Non Approved Inviters
id: 4ad97bf5-a514-41a4-abd3-4f3455ad4865
status: test
description: Detects guest users being invited to tenant by non-approved inviters
references:
    - https://learn.microsoft.com/en-gb/entra/architecture/security-operations-user-accounts#monitoring-external-user-sign-ins
author: MikeDuddington, '@dudders1'
date: 2022-07-28
tags:
    - attack.privilege-escalation
    - attack.persistence
    - attack.initial-access
    - attack.stealth
    - attack.t1078
logsource:
    product: azure
    service: auditlogs
detection:
    selection:
        Category: 'UserManagement'
        OperationName: 'Invite external user'
    filter:
        InitiatedBy|contains: '<approved guest inviter use OR for multiple>'
    condition: selection and not filter
falsepositives:
    - If this was approved by System Administrator.
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not filter

Stage 1: `selection`

selection:
    Category: 'UserManagement'
    OperationName: 'Invite external user'

Stage 2: `not filter`

filter:
    InitiatedBy|contains: '<approved guest inviter use OR for multiple>'

Exclusions

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

Field	Kind	Excluded values
`InitiatedBy`	match	`<approved guest inviter use OR for multiple>`

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
`Category`	eq	`UserManagement`
`OperationName`	eq	`Invite external user`

`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)

Guest Users Invited To Tenant By Non Approved Inviters

MITRE ATT&CK coverage

Event coverage

Rules detecting the same action

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Guest Users Invited To Tenant By Non Approved Inviters

MITRE ATT&CK coverage

Event coverage

Rules detecting the same action

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection

Stage 2: not filter

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter`