A non-privileged user or program can put code and a config file in a known non-privileged path (under C:/usr/local/) that will make curl automatically run the code (as an openssl "engine") on invocation. If that curl is invoked by a privileged user it can do anything it wants. This flaw exists in the official curl-for-windows binaries built and hosted by the curl project (all versions up to and including 7.65.1_1). It does not exist in the curl executable shipped by Microsoft, bundled with Windows 10. It possibly exists in other curl builds for Windows too that uses OpenSSL.