An issue was discovered in Google Santa and molcodesignchecker. A maliciously crafted Universal/fat binary can evade third-party code signing checks. By not completing full inspection of the Universal/fat binary, the user of the third-party tool will believe that the code is signed by Apple, but the malicious unsigned code will execute.
https://www.tenable.com/blog/apple-code-signing-flaw-developers-beware
https://www.okta.com/security-blog/2018/06/issues-around-third-party-apple-code-signing-checks/