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Description

The following analytic detects when a suspicious certificate with a Subject Alternative Name (SAN) is issued using Active Directory Certificate Services (AD CS) and then immediately used for authentication. This detection leverages Windows Security Event Logs, specifically EventCode 4887, to identify the issuance and subsequent use of the certificate. 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 unauthorized access, escalate privileges, and potentially compromise the entire environment.

  • Type: TTP

  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2024-05-24
  • Author: Steven Dick
  • ID: f0306acf-a6ab-437a-bbc6-8628f8d5c97e

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1649 Steal or Forge Authentication Certificates Credential Access
T1550 Use Alternate Authentication Material Defense Evasion, Lateral Movement
Kill Chain Phase
  • Exploitation
NIST
  • DE.CM
CIS20
  • CIS 10
CVE 


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`wineventlog_security` EventCode IN (4887) Attributes="*SAN:*upn*" Attributes="*CertificateTemplate:*" 
| 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 
| rex field=Attributes "(?i)CertificateTemplate:(?<object>[^\r\n]+)" 
| rex field=Attributes "(?i)ccm:(?<req_src>[^\r\n]+)" 
| rex max_match=10 field=Attributes "(?i)(upn=(?<req_user_1>[^\r\n&]+))" 
| rex max_match=10 field=Attributes "(?i)(dns=(?<req_dest_1>[^\r\n&]+))" 
| rex field=Requester "(.+\\\\)?(?<src_user>[^\r\n]+)" 
| rename Attributes as object_attrs, EventCode as signature_id, name as signature, RequestId as ssl_serial, Requester as ssl_subject_common_name 
| eval user = lower(coalesce(req_user_1,req_user_2))  
| join user [ 
| search `wineventlog_security` EventCode=4768 CertThumbprint=* 
| rename TargetUserName as user, Computer as auth_dest, IpAddress as auth_src 
| fields auth_src,auth_dest,user ] 
| eval src = upper(coalesce(auth_src,req_src)), dest = upper(coalesce(auth_dest,req_dest_1,req_dest_2)), risk_score = 90 
| eval flavor_text = case(signature_id=="4887", "User account [".'user'."] authenticated after a suspicious certificate was issued for it by [".'src_user'."] using certificate request ID: ".'ssl_serial') 
| fields - req_* auth_* 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `windows_steal_authentication_certificates___esc1_authentication_filter`

Macros

The SPL above uses the following Macros:

:information_source: windows_steal_authentication_certificates_-_esc1_authentication_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • _time
  • Attributes
  • Computer
  • EventCode
  • Requester
  • RequestId
  • TargetUserName
  • Computer
  • IpAddress

How To Implement

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 for authentication. Sources or templates used in these processes may need to be tuned out for accurate function.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
90.0 100 90 Possible AD CS ESC1 authentication on $dest$

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

Reference

Test Dataset

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 | version: 2