This trivially can't happen in WUFFS. Forget RCE, WUFFS can't even do a traditional Hello World program because (1) you can't do I/O in WUFFS and (2) the language doesn't have strings.

https://github.com/google/wuffs

Very few languages can prevent you writing something like "if(text == "shibboleth") rootshell();" but most languages don't make it trivial to write accidentally.

Pretty much any memory managed language? Java, Go, Rust, Python, pretty much anything other than C/C++ these days is memory safe for security purposes.