Detect Code Signing Certificates in Splunk
Adversaries may create self-signed code signing certificates that can be used during targeting. Code signing is the process of digitally signing executables and scripts to confirm the software author and guarantee that the code has not been altered or corrupted. Adversaries leverage self-signed certificates to make malicious payloads appear more trustworthy — security tools and users are more likely to trust a signed binary even when the signing authority is unknown. Threat actors including Daggerfly (macOS malware), PROMETHIUM (StrongPity spyware installers), and Patchwork (BackConfig RAT) have created self-signed certificates impersonating legitimate software vendors to sign malicious payloads. This technique is commonly paired with T1553.002 (Code Signing) to bypass application allowlisting, reduce user suspicion, and evade detection tooling that weights signed binaries as lower risk.
MITRE ATT&CK
- Tactic
- Resource Development
- Technique
- T1587 Develop Capabilities
- Sub-technique
- T1587.002 Code Signing Certificates
- Canonical reference
- https://attack.mitre.org/techniques/T1587/002/
SPL Detection Query
index=wineventlog sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode=1
| eval Image=lower(Image), CommandLine=lower(CommandLine), ParentImage=lower(ParentImage)
| eval IsMakecert=if(match(Image, "\\\\makecert\.exe$"), 1, 0)
| eval IsPvk2pfx=if(match(Image, "\\\\pvk2pfx\.exe$"), 1, 0)
| eval IsOpenSSL=if(
match(Image, "\\\\openssl\.exe$")
AND (match(CommandLine, "\sreq\s") OR match(CommandLine, "\sx509\s") OR match(CommandLine, "pkcs12") OR match(CommandLine, "genrsa") OR match(CommandLine, "genpkey"))
AND (match(CommandLine, "codesigning") OR match(CommandLine, "1\.3\.6\.1\.5\.5\.7\.3\.3") OR match(CommandLine, "-x509") OR match(CommandLine, "extendedkeyusage")),
1, 0)
| eval IsPowerShellCert=if(
(match(Image, "\\\\powershell\.exe$") OR match(Image, "\\\\pwsh\.exe$"))
AND match(CommandLine, "new-selfsignedcertificate|export-pfxcertificate|export-certificate|x509certificate2|certenroll\.cx509|certificaterequest|codesigning|1\.3\.6\.1\.5\.5\.7\.3\.3"),
1, 0)
| eval IsCertutil=if(
match(Image, "\\\\certutil\.exe$")
AND match(CommandLine, "-addstore|-importpfx"),
1, 0)
| eval IsSigntool=if(
match(Image, "\\\\signtool\.exe$")
AND match(CommandLine, "\ssign"),
1, 0)
| eval SuspicionScore = IsMakecert + IsPvk2pfx + IsOpenSSL + IsPowerShellCert + IsCertutil + IsSigntool
| where SuspicionScore > 0
| eval DetectionCategory=case(
IsMakecert=1, "makecert_native_sdk",
IsPvk2pfx=1, "pvk2pfx_key_conversion",
IsOpenSSL=1, "openssl_code_signing_cert",
IsPowerShellCert=1, "powershell_cert_cmdlet",
IsCertutil=1, "certutil_store_import",
IsSigntool=1, "signtool_executable_signing",
true(), "multi_indicator"
)
| eval IsSuspiciousParent=if(
match(ParentImage, "\\\\(cmd|wscript|mshta|cscript|regsvr32|rundll32|msiexec)\.exe$"),
1, 0)
| eval IsTempPath=if(
match(CommandLine, "\\\\(temp|appdata|downloads|public)\\\\"),
1, 0)
| table _time, host, User, Image, CommandLine, ParentImage, ParentCommandLine,
DetectionCategory, IsSuspiciousParent, IsTempPath, SuspicionScore
| sort - _timeDetects self-signed code signing certificate creation using Sysmon Event ID 1 (Process Creation) logs. Evaluates process image and command line against six detection categories: makecert.exe (Windows SDK), pvk2pfx.exe (key format conversion), openssl with code signing EKU arguments, PowerShell certificate creation cmdlets, certutil store import operations, and signtool signing activity. Each category is scored independently allowing analysts to prioritize multi-indicator events. Suspicious parent process and temp path flags provide additional triage context without requiring analyst lookups.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Software developers creating self-signed certificates for internal code signing during development and testing pipelines
- IT administrators managing internal PKI infrastructure and importing certificates to enterprise certificate stores
- CI/CD build systems (Jenkins, GitHub Actions runners, Azure DevOps agents) that create or use signing certificates as part of release automation
- Security tools such as Fiddler, Burp Suite, and Charles Proxy that create local CA certificates for TLS interception
- Certificate authority enrollment agents and autoenrollment services performing legitimate certutil operations
- macOS developers using codesign tooling through Windows Subsystem for Linux or cross-compilation environments
Other platforms for T1587.002
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 1Create Self-Signed Code Signing Certificate via PowerShell
Expected signal: Sysmon Event ID 1: Process Create with Image=powershell.exe, CommandLine containing 'New-SelfSignedCertificate' and the spoofed Subject. PowerShell ScriptBlock Log Event ID 4104 capturing the full cmdlet invocation with parameters. Sysmon Event ID 11: File Create for df00tech-codesign.pfx in %TEMP%. Sysmon Event ID 13: Registry value set in HKCU\SOFTWARE\Microsoft\SystemCertificates\My\Certificates\<thumbprint>.
- Test 2Create Self-Signed Certificate Using OpenSSL with Code Signing EKU
Expected signal: Sysmon Event ID 1: Two Process Create events — openssl.exe with 'req -x509' and 'extendedKeyUsage=codeSigning' arguments, then openssl.exe with 'pkcs12 -export' arguments. Sysmon Event ID 11: File Creates for df00tech-key.pem, df00tech-cert.pem, df00tech-adobe.pfx in %TEMP%.
- Test 3Sign Executable with Self-Signed Certificate Using signtool.exe
Expected signal: Sysmon Event ID 1: Process Create with Image=signtool.exe, CommandLine containing 'sign' and '/f %TEMP%\df00tech-codesign.pfx'. Sysmon Event ID 11: File modification event for df00tech-signed.exe (PE authenticode signature appended). Security Event ID 4688 (if process command line auditing enabled) capturing full signtool invocation.
- Test 4Import Self-Signed Certificate to Trusted Root Store via certutil
Expected signal: Sysmon Event ID 1: Process Create with Image=certutil.exe, CommandLine containing '-addstore' and 'Root'. Sysmon Event ID 13: Registry value set in HKLM\SOFTWARE\Microsoft\SystemCertificates\Root\Certificates\<thumbprint>. Security Event ID 4657 (registry value modification) if object access auditing is enabled for HKLM\SOFTWARE\Microsoft\SystemCertificates.
References (12)
- https://attack.mitre.org/techniques/T1587/002/
- https://en.wikipedia.org/wiki/Code_signing
- https://www.bitdefender.com/blog/labs/strongpity-apt-new-version-of-the-spyware-phone-targeted-victims-in-turkey-and-syria/
- https://unit42.paloaltonetworks.com/patchwork-apt-southeast-asia/
- https://www.welivesecurity.com/en/eset-research/evasive-panda-apt-group-monitoring-tibetans/
- https://learn.microsoft.com/en-us/windows/win32/seccrypto/makecert
- https://learn.microsoft.com/en-us/windows/win32/seccrypto/signtool
- https://learn.microsoft.com/en-us/powershell/module/pki/new-selfsignedcertificate
- https://learn.microsoft.com/en-us/defender-endpoint/advanced-hunting-deviceprocessevents-table
- https://learn.microsoft.com/en-us/defender-endpoint/advanced-hunting-devicefileevents-table
- https://learn.microsoft.com/en-us/defender-endpoint/advanced-hunting-deviceregistryevents-table
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1587.002/T1587.002.md
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