Detection: Windows Steal Authentication Certificates - ESC1 Abuse

Updated Date: 2024-09-30 ID: cbe761fc-d945-4c8c-a71d-e26d12255d32 Author: Steven Dick Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects when a new certificate is requested or granted against Active Directory Certificate Services (AD CS) using a Subject Alternative Name (SAN). It leverages Windows Security Event Codes 4886 and 4887 to identify these actions. This activity is significant because improperly configured certificate templates can be exploited for privilege escalation and environment compromise. If confirmed malicious, an attacker could gain elevated privileges or persist within the environment, potentially leading to unauthorized access to sensitive information and further exploitation.

Search

 1`wineventlog_security` EventCode IN (4886,4887) Attributes="*SAN:*upn*" Attributes="*CertificateTemplate:*" 
 2| stats count min(_time) as firstTime max(_time) as lastTime values(name) as name values(status) as status values(Subject) as ssl_subject values(SubjectKeyIdentifier) as ssl_hash by Computer, EventCode, Requester, Attributes, RequestId 
 3| `security_content_ctime(firstTime)`  
 4| `security_content_ctime(lastTime)`
 5| fillnull 
 6| rex field=Attributes "(?i)CertificateTemplate:(?<object>[^\r\n]+)" 
 7| rex field=Attributes "(?i)ccm:(?<req_src>[^\r\n]+)" 
 8| rex max_match=10 field=Attributes "(?i)(upn=(?<req_user_1>[^\r\n&]+))" 
 9| rex max_match=10 field=Attributes "(?i)(dns=(?<req_dest_1>[^\r\n&]+))" 
10| rex field=Requester "(.+\\\\)?(?<src_user>[^\r\n]+)" 
11| eval flavor_text = case(EventCode=="4886","A suspicious certificate was requested using request ID: ".'RequestId',EventCode=="4887", "A suspicious certificate was issued using request ID: ".'RequestId'.". To revoke this certifacte use this request ID or the SSL fingerprint [".'ssl_hash'."]"), dest = upper(coalesce(req_dest_1,req_dest_2)), src = upper(coalesce(req_src,Computer)) 
12| fields - req_* 
13| rename Attributes as object_attrs, EventCode as signature_id, name as signature, RequestId as ssl_serial, Requester as ssl_subject_common_name
14| `windows_steal_authentication_certificates___esc1_abuse_filter`

Data Source

Name	Platform	Sourcetype	Source
Windows Event Log Security 4886	Windows	`'xmlwineventlog'`	`'XmlWinEventLog:Security'`
Windows Event Log Security 4887	Windows	`'xmlwineventlog'`	`'XmlWinEventLog:Security'`

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
windows_steal_authentication_certificates___esc1_abuse_filter	`search *`

windows_steal_authentication_certificates___esc1_abuse_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1649	Steal or Forge Authentication Certificates	Credential Access

KillChainPhase.EXPLOITAITON

NistCategory.DE_CM

Cis18Value.CIS_10

APT29

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Notable	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Risk Event	True

This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

To implement this analytic, enhanced Audit Logging must be enabled on AD CS and within Group Policy Management for CS server. See Page 115 of first reference. Recommend throttle correlation by RequestId/ssl_serial at minimum.

Known False Positives

False positives may be generated in environments where administrative users or processes are allowed to generate certificates with Subject Alternative Names. Sources or templates used in these processes may need to be tuned out for accurate function.

Associated Analytic Story

Windows Certificate Services

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
Possible AD CS ESC1 activity by $src_user$ - $flavor_text$	60	100	60

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`XmlWinEventLog:Security`	`XmlWinEventLog`
Integration	✅ Passing	Dataset	`XmlWinEventLog:Security`	`XmlWinEventLog`

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 4