Detect Digital Certificates in Google Chronicle
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/
YARA-L Detection Query
rule t1588_004_unauthorized_certificate_store_modification {
meta:
author = "Detection Engineering"
description = "Detects unauthorized installation of certificates into Windows Trusted Root CA or Intermediate CA certificate stores via registry modification by non-system processes. Adversaries may install rogue certificates to enable MitM attacks or legitimize C2 TLS traffic."
mitre_attack_tactic = "Resource Development"
mitre_attack_technique = "T1588.004"
reference = "https://attack.mitre.org/techniques/T1588/004/"
severity = "HIGH"
confidence = "HIGH"
version = "1.0"
events:
$e.metadata.event_type = "REGISTRY_MODIFICATION"
(
re.regex($e.target.registry.registry_key,
`(?i).*\\SOFTWARE\\Microsoft\\SystemCertificates\\Root\\Certificates.*`) or
re.regex($e.target.registry.registry_key,
`(?i).*\\SOFTWARE\\Microsoft\\SystemCertificates\\CA\\Certificates.*`) or
re.regex($e.target.registry.registry_key,
`(?i).*\\SOFTWARE\\Policies\\Microsoft\\SystemCertificates\\Root.*`) or
re.regex($e.target.registry.registry_key,
`(?i).*\\SOFTWARE\\Policies\\Microsoft\\SystemCertificates\\CA.*`)
)
not re.regex($e.principal.process.file.full_path,
`(?i).*(svchost\.exe|lsass\.exe|wuauclt\.exe|TrustedInstaller\.exe|MicrosoftEdgeUpdate\.exe|MsMpEng\.exe|SgrmBroker\.exe)$`)
condition:
$e
}Chronicle YARA-L 2.0 rule detecting unauthorized modifications to Windows Trusted Root CA and Intermediate CA certificate store registry paths. Matches REGISTRY_MODIFICATION UDM events against all four certificate store key paths and excludes known-legitimate Windows system binaries. Surfaces attacker-controlled processes installing rogue certificates to enable adversary-in-the-middle attacks or trusted C2 communications.
Data Sources
Required Tables
False Positives & Tuning
- Internal enterprise PKI deployment via domain Group Policy Objects (GPOs) where the enforcing process is a domain join or policy application process not included in the current allowlist
- Security product initial installation events where EDR, DLP, or proxy agents write their inspection certificate to the machine root store using a vendor-specific setup binary
- DevOps tooling or CI/CD agents (e.g., Jenkins agent, Ansible runner) executing certificate deployment playbooks as part of automated server provisioning pipelines
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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