Detect Invalid Code Signature in CrowdStrike LogScale
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/
LogScale Detection Query
#event_simpleName = "ProcessRollup2" OR #event_simpleName = "SyntheticProcessRollup2"
| ImageFileName = /./
| SignInfoFlags != "0"
| SignInfoFlags = /(?:invalid|expired|revoked|untrusted)/i
OR (
#event_simpleName = "ClassifiedModuleLoad"
| SignInfoFlags != "0"
| ImageFileName != ""
| SignInfoFlags = /(?:invalid|expired|revoked)/i
)
| groupBy([ComputerName, ImageFileName, SignInfoFlags, SHA256HashData], function=[
count(aid, as=ExecutionCount),
collectDistinct(UserName, as=Users),
collectDistinct(CommandLine, as=CommandLines)
])
| ExecutionCount < 10
| sort(ExecutionCount, order=asc)CrowdStrike LogScale query targeting ProcessRollup2 and ClassifiedModuleLoad events where SignInfoFlags indicate the binary carries a digital signature that is in an invalid, expired, or revoked state. Low execution counts are surfaced first to prioritize novel or targeted activity consistent with T1036.001.
Data Sources
Required Tables
False Positives & Tuning
- CrowdStrike's own sensor update packages or temporary extraction artifacts that are loaded transiently and carry internal test signatures
- Legacy administrative scripts or tooling deployed via GPO that reference binaries signed with enterprise certificates not present in the Falcon trust chain
- Software packaging tools (e.g., NSIS, Inno Setup installers) that wrap signed contents inside an outer installer binary whose signature has separately expired
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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