Auth0 Same Phone Number Shared Across Multiple Users as MFA

Severity: high
Group by: data.details.authenticator.phone_number
Entities: ip_addresses, usernames
Log types: Auth0.Events
Reference: https://github.com/auth0/auth0-customer-detections/tree/main/detections/multiple_phone_numbers_are_registered_as_mfa.yml
Source: github.com/panther-labs/panther-analysis

Detecs when more than one user shares a phone number with another for MFA purposes. Attackers may register their phone number for multiple compromised accounts.

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1098` Account Manipulation

Rule body yaml

AnalysisType: rule
Description: Detecs when more than one user shares a phone number with another for MFA purposes. Attackers may register their phone number for multiple compromised accounts.
DisplayName: "Auth0 Same Phone Number Shared Across Multiple Users as MFA"
Enabled: true
Filename: auth0_same_phone_mfa_multiple_users.py
Runbook: Assess if this was done by the user for a valid business reason. Be vigilant to re-enable this setting as it's in the best security interest for your organization's security posture.
Reference: https://github.com/auth0/auth0-customer-detections/tree/main/detections/multiple_phone_numbers_are_registered_as_mfa.yml
Severity: High
Reports:
  MITRE ATT&CK:
    - TA0003:T1098
DedupPeriodMinutes: 60
LogTypes:
  - Auth0.Events
RuleID: "Auth0.SamePhone.MultipleUsers.MFA"
Threshold: 2
Tests:
  - ExpectedResult: true
    Log:
      data:
        client_id: 1HXWWGKk1Zj3JF8GvMrnCSirccDs4qvr
        client_name: ""
        date: "2025-10-03 14:09:32.149000000"
        description: "Guardian - Enrollment complete (sms)"
        details:
          authenticator:
            phone_number: 1234567891
          request:
            auth:
              credentials:
                jti: 0000000000ecaf1bfbadb06900d22049
              strategy: jwt
              user:
                email: eve@lexcorp.com
                name: Homer Simpson
            channel: https://manage.auth0.com/
            ip: 12.12.12.12
            userAgent: >-
              Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36
              (KHTML, like Gecko) Chrome/1.2.3.4 Safari/537.36
          response:
            body: []
            statusCode: 200
        ip: 12.12.12.12
        log_id: "90020230523204756343781000000000000001223372037583230452"
        type: "gd_enrollment_complete"
        user_agent: >-
          Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML,
          like Gecko) Chrome/1.2.3.4 Safari/537.36
        user_id: google-oauth2|105261262156475850461
      log_id: "90020230523204756343781000000000000001223372037583230452"
      p_any_ip_addresses:
        - 12.12.12.12
      p_any_usernames:
        - google-oauth2|105261262156475850461
      p_event_time: "2023-05-23 20:47:51.149"
      p_log_type: Auth0.Events
      p_parse_time: "2023-05-23 20:49:28.671"
      p_row_id: 00000000004a745ce33b57be383c543e
      p_schema_version: 0
      p_source_id: b9031579-b2c5-45c2-b15c-632b995a4e36
      p_source_label: Org Auth0 Tenant Label
    Name: Shared Phone Number as MFA
  - ExpectedResult: false
    Log:
      data:
        client_id: 1HXWWGKk1Zj3JF8GvMrnCSirccDs4qvr
        client_name: ""
        date: "2025-10-03 14:09:32.149000000"
        description: "Guardian - Enrollment complete (voice)"
        details:
          authenticator:
            phone_number: 1234567891
          request:
            auth:
              credentials:
                jti: 0000000000ecaf1bfbadb06900d22049
              strategy: jwt
              user:
                email: eve@lexcorp.com
                name: Homer Simpson
            channel: https://manage.auth0.com/
            ip: 12.12.12.12
          response:
            body: []
            statusCode: 200
        ip: 12.12.12.12
        log_id: "90020230523204756343781000000000000001223372037583230452"
        type: "gd_enrollment_complete"
        user_id: google-oauth2|105261262156475850461
      p_event_time: "2023-05-23 20:47:51.149"
      p_log_type: Auth0.Events
      p_row_id: 00000000004a745ce33b57be383c543e
      p_source_label: Org Auth0 Tenant Label
    Name: Non-SMS Enrollment (Voice) - No Match
  - ExpectedResult: false
    Log:
      data:
        client_id: 1HXWWGKk1Zj3JF8GvMrnCSirccDs4qvr
        client_name: ""
        date: "2025-10-03 14:09:32.149000000"
        description: "Guardian - Enrollment complete (sms)"
        details:
          authenticator:
            phone_number: ""
          request:
            auth:
              strategy: jwt
              user:
                email: denethor@lotr.com
            channel: https://manage.auth0.com/
            ip: 10.10.10.10
          response:
            body: []
            statusCode: 200
        ip: 10.10.10.10
        type: "gd_enrollment_complete"
        user_id: google-oauth2|888888888888888888888
      p_event_time: "2023-05-23 20:47:51.149"
      p_log_type: Auth0.Events
      p_row_id: 00000000004a745ce33b57be383c543f
      p_source_label: Org Auth0 Tenant Label
    Name: SMS Enrollment Missing Phone Number - No Match

Detection logic

Condition

data.type eq "gd_enrollment_complete"
data.description eq "Guardian - Enrollment complete (sms)"
data.details.authenticator.phone_number is_not_null

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
`data.description`	eq	`Guardian - Enrollment complete (sms)`
`data.details.authenticator.phone_number`	is_not_null	(no value, null check)
`data.type`	eq	`gd_enrollment_complete`

Output fields

Fields the rule emits when it matches. Chronicle authors list these in the outcome block; they appear on the detection and $risk_score drives alerting. Sentinel / Defender XDR rules build them up through project / summarize / extend stages. Sentinel maps these into alert fields via entityMappings and customDetails; Defender XDR custom detections surface them as alert fields directly.

Field	Source
`email`	`data.details.request.auth.user.email`
`user_id`	`data.user_id`
`phone_number`	`data.details.authenticator.phone_number`
`p_source_label`

`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)