Build-time code execution via malicious procedural macro

Code execution in the better-macro Rust crate allows attackers to execute code when a project invokes its println procedural macro. The better_macro::println expansion tries xdg-open, open, and explorer.exe to launch a hard-coded remote URL before emitting normal println code. Execution requires adding the deliberately deceptive crate as a build dependency and compiling code that calls the macro, granting the crate command execution with the build user's privileges.