Code signing provides a level of authenticity on a binary from the developer and a guarantee that the binary has not been tampered with.  However, adversaries are known to use code signing certificates to masquerade malware and tools as legitimate binaries . The certificates used during an operation may be created, forged, or stolen by the adversary.  
Code signing to verify software on first run can be used on modern Windows and macOS/OS X systems. It is not used on Linux due to the decentralized nature of the platform. 
Code signing certificates may be used to bypass security policies that require signed code to execute on a system.
CopyKittens digitally signed an executable with a stolen certificate from legitimate company AI Squared.
Darkhotel has used code-signing certificates on its malware that are either forged due to weak keys or stolen. Darkhotel has also stolen certificates and signed backdoors and downloaders with them.
FIN7 has signed Carbanak payloads with legally purchased code signing certificates. FIN7 has also digitally signed their phishing documents, backdoors and other staging tools to bypass security controls.
Collect and analyze signing certificate metadata on software that executes within the environment to look for unusual certificate characteristics and outliers.
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