↳ GitHub sourceAnalytics ruleHigh
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
'
- Rule type
- Scheduled
- Version
- 1.0.4
- Query frequency
- 1h
- Query period
- 1d
- Trigger
- gt 0
Declared MITRE coverage
Declared sources
Metadata from the source file. No dependencies inferred from KQL.
Connectors
Data types
KQL query
Original query, unchanged.
// 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)
Declared entities
Related content
Links established from declared identifiers and solution manifests.
Source provenance
GitHubDisplayed values come from files in Azure/Azure-Sentinel. They describe the published template, not your workspace configuration.
- Commit
7ca9800↗- Source identifier
cfc1ae62-db63-4a3e-b88b-dc04030c2257
Additional source files 1
Detections/SecurityEvent/ADFSAbnormalEnhancedKeyUsageAttribute-OID.yamlsource ↗GSTEP / CATALOG TRACKING
Added to catalog : 16 Sept 2026 · 05:49 UTC
Last change observed : 16 Sept 2026 · 05:49 UTC