AD FS Abnormal EKU object identifier attribute

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Id	cfc1ae62-db63-4a3e-b88b-dc04030c2257
Rulename	AD FS Abnormal EKU object identifier attribute
Description	This detection uses Security events from the “AD FS Auditing” provider to detect suspicious object identifiers (OIDs) as part EventID 501 and specifically part of the Enhanced Key Usage attributes. This query checks to see if you have any new OIDs in the last hour that have not been seen in the previous day. New OIDs should be validated and OIDs that are very long, as indicated by the OID_Length field, could also be an indicator of malicious activity. In order to use this query you need to enable AD FS auditing on the AD FS Server. References: https://www.microsoft.com/security/blog/2022/08/24/magicweb-nobeliums-post-compromise-trick-to-authenticate-as-anyone/ https://docs.microsoft.com/windows-server/identity/ad-fs/troubleshooting/ad-fs-tshoot-logging
Severity	High
Tactics	CredentialAccess
Techniques	T1552
Required data connectors	SecurityEvents
Kind	Scheduled
Query frequency	1h
Query period	1d
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Detections/SecurityEvent/ADFSAbnormalEnhancedKeyUsageAttribute-OID.yaml
Version	1.0.4
Arm template	cfc1ae62-db63-4a3e-b88b-dc04030c2257.json

KQL

// change the starttime value for a longer period of known OIDs
let starttime = 1d;
// change the lookback value for a longer period of lookback for suspicious/abnormal
let lookback = 1h;
let OIDList = SecurityEvent
| where TimeGenerated >= ago(starttime)
| where EventSourceName == 'AD FS Auditing'
| where EventID == 501
| where EventData has '/eku'
| extend OIDs = extract_all(@"<Data>([\d+\.]+)</Data>", EventData)
| mv-expand OIDs
| extend OID = tostring(OIDs)
| extend OID_Length = strlen(OID)
| project TimeGenerated, Computer, EventSourceName, EventID, OID, OID_Length, EventData
;
OIDList
| where TimeGenerated >= ago(lookback)
| join kind=leftanti (
OIDList
| where TimeGenerated between (ago(starttime) .. ago(lookback))
| summarize by OID
) on OID
| extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))
| extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)

YAML

relevantTechniques:
- T1552
name: AD FS Abnormal EKU object identifier attribute
queryFrequency: 1h
version: 1.0.4
triggerThreshold: 0
severity: High
metadata:
  support:
    tier: Community
  categories:
    domains:
    - Security - Others
    - Identity
  source:
    kind: Community
  author:
    name: Microsoft Security Research
requiredDataConnectors:
- connectorId: SecurityEvents
  dataTypes:
  - SecurityEvent
tactics:
- CredentialAccess
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/SecurityEvent/ADFSAbnormalEnhancedKeyUsageAttribute-OID.yaml
query: |
  // change the starttime value for a longer period of known OIDs
  let starttime = 1d;
  // change the lookback value for a longer period of lookback for suspicious/abnormal
  let lookback = 1h;
  let OIDList = SecurityEvent
  | where TimeGenerated >= ago(starttime)
  | where EventSourceName == 'AD FS Auditing'
  | where EventID == 501
  | where EventData has '/eku'
  | extend OIDs = extract_all(@"<Data>([\d+\.]+)</Data>", EventData)
  | mv-expand OIDs
  | extend OID = tostring(OIDs)
  | extend OID_Length = strlen(OID)
  | project TimeGenerated, Computer, EventSourceName, EventID, OID, OID_Length, EventData
  ;
  OIDList
  | where TimeGenerated >= ago(lookback)
  | join kind=leftanti (
  OIDList
  | where TimeGenerated between (ago(starttime) .. ago(lookback))
  | summarize by OID
  ) on OID
  | extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))
  | extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)  
entityMappings:
- fieldMappings:
  - columnName: Computer
    identifier: FullName
  - columnName: HostName
    identifier: HostName
  - columnName: HostNameDomain
    identifier: DnsDomain
  entityType: Host
queryPeriod: 1d
triggerOperator: gt
id: cfc1ae62-db63-4a3e-b88b-dc04030c2257
tags:
- Nobelium
- MagicWeb
kind: Scheduled
description: |
  'This detection uses Security events from the "AD FS Auditing" provider to detect suspicious object identifiers (OIDs) as part EventID 501 and specifically part of the Enhanced Key Usage attributes.
  This query checks to see if you have any new OIDs in the last hour that have not been seen in the previous day. New OIDs should be validated and OIDs that are very long, as indicated
  by the OID_Length field, could also be an indicator of malicious activity.
  In order to use this query you need to enable AD FS auditing on the AD FS Server.
  References:
  https://www.microsoft.com/security/blog/2022/08/24/magicweb-nobeliums-post-compromise-trick-to-authenticate-as-anyone/
  https://docs.microsoft.com/windows-server/identity/ad-fs/troubleshooting/ad-fs-tshoot-logging
  '

ARM