Detect Code Signing Certificates in Google Chronicle
Adversaries may buy and/or steal code signing certificates to sign malicious payloads, enabling their software to appear legitimate and bypass security controls that trust signed code. Code signing provides authenticity guarantees that cause users and security tools to trust signed executables more readily than unsigned binaries. Adversaries purchase certificates using front organizations or stolen identity information, or directly steal signing materials from compromised third parties. Real-world threat actors including Wizard Spider (DigiCert, GlobalSign certs), OilRig, BlackTech, MegaCortex (fake company certificates), and Kimsuky have all leveraged stolen or fraudulently-obtained code signing certificates. Detection pivots to observable artifacts when signed malicious code executes in the environment: certificate anomalies (revoked, expired, recently-issued, or from unusual certificate authorities), discrepancies between file metadata and certificate subjects, Windows Code Integrity enforcement events, and low-prevalence signed executables executing from user-writable paths.
MITRE ATT&CK
- Tactic
- Resource Development
- Technique
- T1588 Obtain Capabilities
- Sub-technique
- T1588.003 Code Signing Certificates
- Canonical reference
- https://attack.mitre.org/techniques/T1588/003/
YARA-L Detection Query
rule t1588_003_suspicious_cert_execution {
meta:
author = "Argus Detection Engineering"
description = "Detects signed executables with anomalous certificate status (revoked, expired, invalid, untrusted root) executing from user-writable paths — T1588.003"
mitre_attack_tactic = "Resource Development"
mitre_attack_technique = "T1588.003"
severity = "HIGH"
confidence = "MEDIUM"
reference = "https://attack.mitre.org/techniques/T1588/003/"
created = "2024-01-01"
events:
$e.metadata.event_type = "PROCESS_LAUNCH"
re.regex(
$e.target.process.file.full_path,
`(?i)(\\AppData\\|\\Temp\\|\\Downloads\\|\\Users\\Public\\|\\ProgramData\\)`
)
(
$e.target.file.authenticode.trusted_by_os = false
or $e.target.file.authenticode.result = "SIGNATURE_EXPIRED"
or $e.target.file.authenticode.result = "SIGNATURE_REVOKED"
or $e.target.file.authenticode.result = "SIGNATURE_UNTRUSTED_ROOT"
or $e.target.file.authenticode.result = "SIGNATURE_INVALID"
)
not re.regex(
$e.target.file.authenticode.signer,
`(?i)(Microsoft Corporation|Microsoft Windows|Google LLC|Adobe Inc|Oracle America|Intel Corporation|NVIDIA|Cisco Systems|VMware|Apple Inc|Amazon\.com)`
)
condition:
$e
}Chronicle YARA-L 2.0 rule matching UDM PROCESS_LAUNCH events where the executed binary resides in a user-writable directory and carries an anomalous Authenticode result. Relies on Chronicle's target.file.authenticode UDM enrichment populated by the Windows Sysmon or Endpoint telemetry parser. The authenticode.result field reflects the Windows trust verification outcome as Chronicle normalizes it from Sysmon XML. Note: authenticode UDM fields must be enabled in the Chronicle parser configuration for your Windows log source.
Data Sources
Required Tables
False Positives & Tuning
- Enterprise applications deployed via user-profile-based software delivery mechanisms where the signing certificate chain includes an intermediate CA that Chronicle's UDM Authenticode enrichment cannot fully resolve to a known trusted root, causing trusted_by_os to be populated as false
- Legitimate portable executables downloaded and run directly from the Downloads folder — particularly open-source tooling and utilities from smaller ISVs — where the signer name does not match any entry in the known-publisher exclusion regex
- SOC analysts or IR responders executing signed forensic tools (Sysinternals, Velociraptor, KAPE) directly from their own Downloads or Desktop folders during incident investigation activities on monitored endpoints
Other platforms for T1588.003
Testing Methodology
Validate this detection against 5 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 1Create Self-Signed Code Signing Certificate and Sign Test Binary
Expected signal: Sysmon Event ID 11 (File Create): argus_signed_test.exe created in %TEMP%. Sysmon Event ID 1 (Process Create): powershell.exe spawning csc.exe (C# compiler) to build the test binary. Sysmon Event ID 13 (Registry Value Set): certificate written to HKCU\SOFTWARE\Microsoft\SystemCertificates\My\. DeviceFileEvents in MDE: file creation event for the test executable in user temp path.
- Test 2Inspect Authenticode Certificate Chain on Suspicious Executable
Expected signal: Sysmon Event ID 11 (File Create): argus_lolbin_test.exe in %TEMP%. Sysmon Event ID 1 (Process Create): certutil.exe with -verify -urlfetch flags and temp path argument. Sysmon Event ID 3 (Network Connection): certutil.exe making outbound HTTPS connections to Microsoft CRL distribution points (crl.microsoft.com, ocsp.msocsp.com) for revocation checking. DeviceProcessEvents: certutil.exe spawned from PowerShell/cmd.exe.
- Test 3Enumerate Code Signing Certificates Including Private Key Holders
Expected signal: Sysmon Event ID 1 (Process Create): PowerShell accessing multiple certificate stores. Sysmon Event ID 11 (File Create): codesign_enum.csv created in %TEMP%. DeviceRegistryEvents: reads to HKLM\SOFTWARE\Microsoft\SystemCertificates\{My,Root,CA,TrustedPublisher}. DeviceFileEvents in MDE: CSV output file creation in user temp directory.
- Test 4Validate Executable Signatures Using Sigcheck Sysinternals Tool
Expected signal: Sysmon Event ID 1 (Process Create): sigcheck.exe launching from %TEMP% with -a -h flags. Sysmon Event ID 3 (Network Connection): sigcheck.exe may attempt outbound connection to VirusTotal API if -vt flag is included. DeviceProcessEvents: sigcheck.exe spawned by PowerShell with the target path argument covering %TEMP% executables.
- Test 5Query Windows Code Integrity Logs for Historical Certificate Enforcement Events
Expected signal: Sysmon Event ID 1 (Process Create): PowerShell executing Get-WinEvent against the Code Integrity operational log. DeviceProcessEvents: PowerShell with Get-WinEvent in command line. If any Code Integrity events were previously logged on this system (e.g., from WDAC policy enforcement), they will be returned. In environments without WDAC policy configured, Event IDs 3033/3034 may not appear, but 3036 (certificate details) often does.
References (10)
- https://attack.mitre.org/techniques/T1588/003/
- https://en.wikipedia.org/wiki/Code_signing
- https://learn.microsoft.com/en-us/microsoft-365/security/defender/advanced-hunting-devicefilecertificateinfo-table
- https://learn.microsoft.com/en-us/sysinternals/downloads/sigcheck
- https://learn.microsoft.com/en-us/windows/security/threat-protection/windows-defender-application-control/event-id-explanations
- https://crt.sh/
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1588.003/T1588.003.md
- https://www.mandiant.com/resources/blog/fin12-ransomware-intrusion-actor-pursuing-high-value-targets
- https://symantec-enterprise-blogs.security.com/blogs/threat-intelligence/palmerworm-espionage-apt-target-taiwan
- https://www.ibm.com/reports/threat-intelligence
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