AD FS Abnormal EKU object identifier attribute

Severity: high
Time window: 1d
Group by: OID
Author: Microsoft Security Research
Source: github.com/Azure/Azure-Sentinel

'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 '

MITRE ATT&CK coverage

Tactic	Techniques
Credential Access	`T1552` Unsecured Credentials

Rule body kusto

id: cfc1ae62-db63-4a3e-b88b-dc04030c2257
name: 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
requiredDataConnectors:
  - connectorId: SecurityEvents
    dataTypes:
      - SecurityEvent
queryFrequency: 1h
queryPeriod: 1d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - CredentialAccess
relevantTechniques:
  - T1552
tags:
  - Nobelium
  - MagicWeb
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:
  - entityType: Host
    fieldMappings:
      - identifier: FullName
        columnName: Computer
      - identifier: HostName
        columnName: HostName
      - identifier: DnsDomain
        columnName: HostNameDomain
version: 1.0.4
kind: Scheduled
metadata:
    source:
        kind: Community
    author:
        name: Microsoft Security Research
    support:
        tier: Community
    categories:
        domains: [ "Security - Others", "Identity" ]

Stages and Predicates

Parameters

let starttime = 1d;
let lookback = 1h;

The stages below define let OIDList (the rule's main pipeline source).

Stage 1: `source`

let OIDList

Stage 2: `source`

SecurityEvent

Stage 3: `where`

| where TimeGenerated >= ago(starttime)

Stage 4: `where`

| where EventSourceName == 'AD FS Auditing'

Stage 5: `where`

| where EventID == 501

Stage 6: `where`

| where EventData has '/eku'

Stage 7: `extend`

| extend OIDs = extract_all(@"<Data>([\d+\.]+)</Data>", EventData)

Stage 8: `mv-expand`

| mv-expand OIDs

Stage 9: `extend`

| extend OID = tostring(OIDs)

Stage 10: `extend`

| extend OID_Length = strlen(OID)

Stage 11: `project`

| project TimeGenerated, Computer, EventSourceName, EventID, OID, OID_Length, EventData

The stages below run on OIDList (the outer pipeline).

Stage 12: `where`

OIDList
| where TimeGenerated >= ago(lookback)

Stage 13: `join` (negated)

| join kind=leftanti (
OIDList
| where TimeGenerated between (ago(starttime) .. ago(lookback))
| summarize by OID
) on OID

Stage 14: `extend`

| extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))

Stage 15: `extend`

| extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)

HostNameDomain =

ifDomainIndex != -1substring(Computer, (DomainIndex + 1))

elseComputer

Stage 16: `summarize`

summarize by OID

Exclusions

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

Field	Kind	Excluded values
`EventData`	match	`/eku`
`EventID`	eq	`501`
`EventSourceName`	eq	`AD FS Auditing`

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
`EventData`	match	`/eku` transforms: `term`
`EventID`	eq	`501` transforms: `cased` corpus 2 (kusto 2)
`EventSourceName`	eq	`AD FS Auditing` transforms: `cased`

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
`OID`	`summarize`

`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)

AD FS Abnormal EKU object identifier attribute

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Stage 1: `source`

Stage 2: `source`

Stage 3: `where`

Stage 4: `where`

Stage 5: `where`

Stage 6: `where`

Stage 7: `extend`

Stage 8: `mv-expand`

Stage 9: `extend`

Stage 10: `extend`

Stage 11: `project`

Stage 12: `where`

Stage 13: `join` (negated)

Stage 14: `extend`

Stage 15: `extend`

Stage 16: `summarize`

Exclusions

Indicators

Output fields

Keyboard shortcuts

Search operators

AD FS Abnormal EKU object identifier attribute

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Stage 1: source

Stage 2: source

Stage 3: where

Stage 4: where

Stage 5: where

Stage 6: where

Stage 7: extend

Stage 8: mv-expand

Stage 9: extend

Stage 10: extend

Stage 11: project

Stage 12: where

Stage 13: join (negated)

Stage 14: extend

Stage 15: extend

Stage 16: summarize

Exclusions

Indicators

Output fields

Stage 1: `source`

Stage 2: `source`

Stage 3: `where`

Stage 4: `where`

Stage 5: `where`

Stage 6: `where`

Stage 7: `extend`

Stage 8: `mv-expand`

Stage 9: `extend`

Stage 10: `extend`

Stage 11: `project`

Stage 12: `where`

Stage 13: `join` (negated)

Stage 14: `extend`

Stage 15: `extend`

Stage 16: `summarize`