Detect Invalid Code Signature in Splunk
Adversaries may attempt to mimic features of valid code signatures to increase the chance of deceiving a user, analyst, or tool. Code signing provides a level of authenticity on a binary from the developer and a guarantee that the binary has not been tampered with. Adversaries can copy the metadata and signature information from a signed program, then use it as a template for an unsigned program. Files with invalid code signatures will fail digital signature validation checks, but they may appear more legitimate to users and security tools may improperly handle these files. Unlike Code Signing (T1553.002), this activity will not result in a valid signature.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1036 Masquerading
- Sub-technique
- T1036.001 Invalid Code Signature
- Canonical reference
- https://attack.mitre.org/techniques/T1036/001/
SPL Detection Query
index=wineventlog sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode=7
| where SignatureStatus!="Valid"
| where isnotnull(Signature) AND Signature!="?"
| eval SignedButInvalid=if(SignatureStatus IN ("Invalid", "Expired", "Revoked", "Untrusted"), 1, 0)
| where SignedButInvalid=1
| stats count as Executions, values(SignatureStatus) as SigStatus, dc(host) as Hosts by Image, Signature, Signed
| where Executions < 10
| sort - ExecutionsDetects loaded images (DLLs and executables) with invalid code signatures using Sysmon Event ID 7 (Image Loaded). Filters for signature states indicating tampering, expiry, or revocation. Low execution counts across few hosts suggest targeted malware rather than widespread legitimate software.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Expired certificates on legitimate but outdated software that has not been updated
- Self-signed certificates used by internal development or testing tools
- Legitimate software with misconfigured or incomplete signing (common in some open-source tools)
Other platforms for T1036.001
Testing Methodology
Validate this detection against 3 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 1Sign Binary with Invalid Self-Signed Certificate
Expected signal: Sysmon Event ID 7: ImageLoaded with SignatureStatus=Untrusted and Signature containing 'Microsoft Corporation'. Process creation event for test_signed.exe.
- Test 2Copy Signature Metadata with SigThief
Expected signal: Sysmon Event ID 1: Process creation for PowerShell examining signature metadata. File creation events for both binaries in temp directory.
- Test 3Execute Binary with Expired Certificate (Simulated)
Expected signal: PowerShell ScriptBlock Logging Event ID 4104 showing certificate creation. Sysmon Event ID 1 for PowerShell process.
References (6)
- https://attack.mitre.org/techniques/T1036/001/
- https://threatexpress.com/blogs/2017/metatwin-borrowing-microsoft-metadata-and-digital-signatures-to-hide-binaries/
- https://github.com/secretsquirrel/SigThief
- https://learn.microsoft.com/en-us/sysinternals/downloads/sigcheck
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1036.001/T1036.001.md
- https://posts.specterops.io/code-signing-certificate-cloning-attacks-and-defenses-6f98657fc6ec
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