Entra ID Device Registration with Phishing Kit Default OS Build

  1[metadata]
  2creation_date = "2026/06/29"
  3integration = ["azure"]
  4maturity = "production"
  5updated_date = "2026/06/29"
  6
  7[rule]
  8author = ["Elastic"]
  9description = """
 10Identifies a Microsoft Entra ID device registration where the recorded cloud device operating system build is
 11"10.0.19045.2006" and the device display name follows the default "DESKTOP-" pattern. This is the frozen default device
 12profile observed when adversary-in-the-middle (AiTM) phishing kits such as Tycoon2FA and Kali365 register Azure
 13AD-joined devices after capturing a victim session, in order to acquire a Primary Refresh Token (PRT) and establish
 14persistence. The build is hardcoded by the tooling and it is uncommon for the OS build to match this exact value across
 15an environment of otherwise patched hosts, where a current Windows 10 22H2 device reports a far higher
 16"10.0.19045.<revision>" value.
 17"""
 18false_positives = [
 19    """
 20    Legitimate device registrations may coincidentally use the `10.0.19045.2006` build (Windows 10 22H2) with a default
 21    `DESKTOP-` hostname, particularly on imaged or unmanaged Windows hosts that have not been updated. Validate against
 22    your device inventory, expected provisioning workflows, and the registering user before escalating.
 23    """,
 24    """
 25    Authorized red team or penetration testing engagements that register devices with this OS profile will match this
 26    rule. If this is expected, add exceptions for the specific user principal names, source IPs, or device names
 27    involved.
 28    """,
 29]
 30from = "now-9m"
 31index = ["logs-azure.auditlogs-*"]
 32language = "kuery"
 33license = "Elastic License v2"
 34name = "Entra ID Device Registration with Phishing Kit Default OS Build"
 35note = """## Triage and analysis
 36
 37### Investigating Entra ID Device Registration with Phishing Kit Default OS Build
 38
 39AiTM phishing kits including Tycoon2FA and Kali365 register a device in Entra ID with a frozen default cloud device OS build of `10.0.19045.2006` and a default display name of `DESKTOP-<random characters>`. This build is hardcoded by the tooling and differs from the OS version of legitimate, patched hosts (a current Windows 10 22H2 device reports a much higher `10.0.19045.<revision>` value), making the build a useful indicator of kit-driven device registration. Rogue device registration is typically a precursor to Primary Refresh Token (PRT) acquisition, MFA/Conditional Access bypass, and persistent token-based access.
 40
 41The matching Entra ID audit event is an `Add device` operation initiated by the `Device Registration Service`, where the modified properties record the registered device characteristics:
 42
 43- `azure.auditlogs.properties.target_resources.0.modified_properties.3` (`CloudDeviceOSVersion`) = `10.0.19045.2006`
 44- `azure.auditlogs.properties.target_resources.0.modified_properties.4` (`CloudDisplayName`) = `DESKTOP-*`
 45
 46### Possible investigation steps
 47
 48- Confirm the registering identity via `azure.auditlogs.properties.initiated_by.user.userPrincipalName` and determine whether that user is expected to register a new device.
 49- Review `azure.auditlogs.identity` to confirm the `Device Registration Service` initiated the request, and use `azure.correlation_id` to pivot across the full registration flow (`Add device`, `Add registered users to device`, `Add registered owner to device`).
 50- Inspect the device name in `azure.auditlogs.properties.target_resources.0.display_name`; kit-registered names are commonly `DESKTOP-` followed by 6 alphanumeric (Tycoon2FA) or 6 hexadecimal (Kali365) characters.
 51- Inspect the registration user agent on the paired `Register device` event (`azure.auditlogs.properties.userAgent`), which is frequently a spoofed `Dsreg/10.0 (Windows 10.0.19045.2006)` string or a raw HTTP client such as `axios/*` or `python-requests/*`.
 52- Check whether the same user registered multiple devices in a short window (a single piece of kit infrastructure registering several devices is common for PRT persistence at scale).
 53- Review `azure.auditlogs.properties.initiated_by.user.ipAddress` and geolocation for the registration source. Flag unexpected IPs, hosting/VPS ASNs (for example Tencent or Alibaba), or impossible-travel relative to the user's normal activity.
 54- Pivot to `azure.signinlogs` for the same user and timeframe and look for follow-on sign-ins where the incoming token type is a `primaryRefreshToken`, for AiTM sign-ins immediately preceding the registration, or for the broker subsequently minting tokens for other resources such as Microsoft Graph.
 55
 56### False positive analysis
 57
 58- Unmanaged or never-patched Windows 10 22H2 hosts may legitimately present the `10.0.19045.2006` build with a default `DESKTOP-` hostname. Validate against device inventory and known provisioning programs.
 59- Authorized security assessments that register devices with this OS profile will match. Document the engagement and add scoped exceptions.
 60
 61### Response and remediation
 62
 63- If confirmed malicious, remove the registered device from Entra ID and revoke the user's refresh tokens and primary refresh tokens. Remove the device BEFORE revoking sessions, because device-bound PRTs survive `revokeSignInSessions`.
 64- Disable the account or reset credentials per policy and review for additional persistence (attacker-registered MFA methods, added owners, app registrations, or service principal credentials).
 65- Conduct historical analysis using `azure.correlation_id` and the registering user to determine scope of access.
 66- Tighten device registration and join controls via Conditional Access (restrict who can register/join devices and require MFA for registration).
 67"""
 68references = [
 69    "https://any.run/malware-trends/tycoon/",
 70    "https://www.huntress.com/blog/kali365-device-code-phishing-kit",
 71    "https://any.run/malware-trends/kali365/",
 72    "https://arcticwolf.com/resources/blog/token-bingo-dont-let-your-code-be-the-winner/",
 73    "https://www.ic3.gov/PSA/2026/PSA260521",
 74]
 75risk_score = 47
 76rule_id = "82629eed-5516-446e-ad73-03b8c4f4d571"
 77severity = "medium"
 78tags = [
 79    "Domain: Cloud",
 80    "Domain: Identity",
 81    "Data Source: Azure",
 82    "Data Source: Microsoft Entra ID",
 83    "Data Source: Microsoft Entra ID Audit Logs",
 84    "Use Case: Identity and Access Audit",
 85    "Use Case: Threat Detection",
 86    "Threat: Tycoon2FA",
 87    "Threat: Kali365",
 88    "Tactic: Persistence",
 89    "Resources: Investigation Guide",
 90]
 91timestamp_override = "event.ingested"
 92type = "query"
 93
 94query = '''
 95data_stream.dataset:"azure.auditlogs" and event.action:"Add device" and
 96    azure.auditlogs.properties.target_resources.0.modified_properties.3.new_value:*10.0.19045.2006* and
 97    azure.auditlogs.properties.target_resources.0.modified_properties.4.new_value:*DESKTOP-*
 98'''
 99
100
101[[rule.threat]]
102framework = "MITRE ATT&CK"
103[[rule.threat.technique]]
104id = "T1098"
105name = "Account Manipulation"
106reference = "https://attack.mitre.org/techniques/T1098/"
107[[rule.threat.technique.subtechnique]]
108id = "T1098.005"
109name = "Device Registration"
110reference = "https://attack.mitre.org/techniques/T1098/005/"
111
112
113
114[rule.threat.tactic]
115id = "TA0003"
116name = "Persistence"
117reference = "https://attack.mitre.org/tactics/TA0003/"
118
119[rule.investigation_fields]
120field_names = [
121    "@timestamp",
122    "event.action",
123    "event.outcome",
124    "azure.auditlogs.identity",
125    "azure.auditlogs.operation_name",
126    "azure.auditlogs.properties.target_resources.0.display_name",
127    "azure.auditlogs.properties.target_resources.0.modified_properties.3.new_value",
128    "azure.auditlogs.properties.target_resources.0.modified_properties.4.new_value",
129    "azure.auditlogs.properties.initiated_by.user.userPrincipalName",
130    "azure.auditlogs.properties.initiated_by.user.ipAddress",
131    "azure.correlation_id",
132]