Detect Digital Certificates in Splunk
Adversaries may buy and/or steal SSL/TLS certificates that can be used during targeting. SSL/TLS certificates are designed to instill trust. They include information about the key, information about its owner's identity, and the digital signature of an entity that has verified the certificate's contents are correct. Adversaries may purchase or steal SSL/TLS certificates to further their operations, such as encrypting C2 traffic or enabling Adversary-in-the-Middle attacks if the certificate is trusted or added to the root of trust. Free certificate authorities (e.g., Let's Encrypt) enable adversaries to acquire certificates at no cost. Compromised certificate authority infrastructure (e.g., DigiNotar) allows issuance of fraudulent certificates for any domain. After obtaining a digital certificate, an adversary may install it on infrastructure under their control to legitimize malicious communications.
MITRE ATT&CK
- Tactic
- Resource Development
- Technique
- T1588 Obtain Capabilities
- Sub-technique
- T1588.004 Digital Certificates
- Canonical reference
- https://attack.mitre.org/techniques/T1588/004/
SPL Detection Query
index=wineventlog sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" (EventCode=12 OR EventCode=13)
(
TargetObject="*\\SOFTWARE\\Microsoft\\SystemCertificates\\Root\\Certificates*"
OR TargetObject="*\\SOFTWARE\\Microsoft\\SystemCertificates\\CA\\Certificates*"
OR TargetObject="*\\SOFTWARE\\Policies\\Microsoft\\SystemCertificates\\Root*"
OR TargetObject="*\\SOFTWARE\\Policies\\Microsoft\\SystemCertificates\\CA*"
)
| where NOT (
match(Image, "(?i)(svchost\.exe|lsass\.exe|wuauclt\.exe|TrustedInstaller\.exe|MicrosoftEdgeUpdate\.exe|MsMpEng\.exe|SgrmBroker\.exe)$")
)
| eval StoreType=case(
match(TargetObject, "Root\\Certificates"), "Trusted Root CA",
match(TargetObject, "CA\\Certificates"), "Intermediate CA",
true(), "Other"
)
| rex field=TargetObject "Certificates\\(?<cert_thumbprint>[A-F0-9]{40})" max_match=1
| eval EventType=case(EventCode="12", "RegistryKeyCreate", EventCode="13", "RegistryValueSet", true(), "Unknown")
| table _time, host, User, EventType, StoreType, cert_thumbprint, TargetObject, Image, CommandLine, ParentImage
| sort - _timeDetects certificate store modifications using Sysmon Event ID 12 (Registry Key Create/Delete) and 13 (Registry Value Set) targeting Windows certificate trust store registry paths. Extracts the certificate thumbprint from the registry object path for use in downstream threat intelligence lookups. Excludes known-legitimate OS and security processes. Focuses on unexpected processes (PowerShell, cmd.exe, scripting engines, unsigned installers) modifying the Root or CA certificate stores.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Enterprise software deployments pushing corporate root CA certificates via SCCM, Intune, or GPO
- Browser auto-updates refreshing bundled root certificate stores via their own update binaries
- VPN or SSL inspection proxy agents installing TLS inspection root certificates during endpoint enrollment
- Security tool deployments (EDR, DLP) that add their own CA certificates for local inspection
Other platforms for T1588.004
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Install Self-Signed Root Certificate via certutil
Expected signal: Sysmon Event ID 13 (RegistryValueSet) with TargetObject = HKLM\SOFTWARE\Microsoft\SystemCertificates\Root\Certificates\<thumbprint>. Sysmon Event ID 1 for certutil.exe with CommandLine containing '-addstore Root'. Sysmon Event ID 1 for powershell.exe with CommandLine containing 'New-SelfSignedCertificate' and 'Export-Certificate'. DeviceRegistryEvents (MDE) showing ActionType=RegistryValueSet on the Root certificate store path with InitiatingProcessFileName=certutil.exe.
- Test 2Install Certificate via PowerShell Import-Certificate
Expected signal: Sysmon Event ID 13 (RegistryValueSet) with TargetObject containing Root\Certificates\<thumbprint> and initiating process powershell.exe. PowerShell ScriptBlock Log Event ID 4104 capturing the full script including 'Import-Certificate' targeting 'Cert:\LocalMachine\Root'. Sysmon Event ID 11 (FileCreate) for the temporary .cer file in %TEMP%.
- Test 3Enumerate Certificate Stores for Pre-Attack Reconnaissance
Expected signal: Sysmon Event ID 1 for certutil.exe with CommandLine containing '-store Root' and '-store CA'. Sysmon Event ID 1 for powershell.exe with CommandLine containing 'Get-ChildItem Cert:' and 'HasPrivateKey'. PowerShell ScriptBlock Log Event ID 4104 capturing full certificate enumeration script.
- Test 4Download and Install Certificate from Remote URL via certutil URLCache
Expected signal: Sysmon Event ID 1 for certutil.exe with CommandLine containing '-urlcache -split -f http://'. Sysmon Event ID 3 (NetworkConnection) for certutil.exe connecting to 127.0.0.1:8080 (or external IP in real attacks). DeviceProcessEvents CommandLine field captures the URL attempted. Download attempt generates telemetry regardless of server availability.
References (9)
- https://attack.mitre.org/techniques/T1588/004/
- https://threatpost.com/final-report-diginotar-hack-shows-total-compromise-ca-servers-103112/77170/
- https://www.splunk.com/en_us/blog/security/tall-tales-of-hunting-with-tls-ssl-certificates.html
- https://letsencrypt.org/docs/faq/
- https://crt.sh
- https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/certutil
- https://learn.microsoft.com/en-us/powershell/module/pki/import-certificate
- https://www.recordedfuture.com/research/cobalt-strike-servers
- https://docs.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4104
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