Detection: Windows Steal Authentication Certificates CS Backup

Updated Date: 2024-05-11 ID: a2f4cc7f-6503-4078-b206-f83a29f408a7 Author: Michael Haag, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic identifies the backup of the Active Directory Certificate Services (AD CS) store, detected via Event ID 4876. This event is logged when a backup is performed using the CertSrv.msc UI or the CertUtil.exe -BackupDB command. Monitoring this activity is crucial as unauthorized backups can indicate an attempt to steal authentication certificates, which are critical for secure communications. If confirmed malicious, this activity could allow an attacker to impersonate users, escalate privileges, or access sensitive information, severely compromising the security of the environment.

1`wineventlog_security` EventCode=4876
2| stats count min(_time) as firstTime max(_time) as lastTime by dest, name, action, Caller_Domain ,Caller_User_Name 
3| `security_content_ctime(firstTime)` 
4| `security_content_ctime(lastTime)` 
5| `windows_steal_authentication_certificates_cs_backup_filter`

Data Source

Name Platform Sourcetype Source Supported App
Windows Event Log Security 4876 Windows icon Windows 'xmlwineventlog' 'XmlWinEventLog:Security' N/A

Macros Used

Name Value
security_content_ctime convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)
windows_steal_authentication_certificates_cs_backup_filter search *
windows_steal_authentication_certificates_cs_backup_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_AE
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 Risk Event True
This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

To implement this analytic, enhanced Audit Logging must be enabled on AD CS and within Group Policy Management for CS server. See Page 128 of first reference.

Known False Positives

False positives will be generated based on normal certificate store backups. Leave enabled to generate Risk, as this is meant to be an anomaly analytic. If CS backups are not normal, enable as TTP.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
The Active Directory Certiciate Services was backed up on $dest$. 40 50 80
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: 2