There's a lot of good information in here, but if you think this is a time to go all language supremicist about how much better your language is and how this proves Go sucks, you might want to double-check the CVE database real quick first. A lot of these issues are more attributable to plain ol' user error and the fundamental messiness of JSON and XML than Go qua Go and I've seen many similar issues everywhere.

For instance, there simply isn't a "correct" way for a parser to handle duplicate keys. Because the problem they have is different layers seeing them differently, you can have the problem anywhere duplicate keys are treated differently, and it's not like Go is the only thing to implement "last wins". It doesn't matter what you do. Last wins? Varies from the many "first wins" implementations. First wins? Varies from the many "last wins" implementations. Nondeterministically choose? Now you conflict with everyone, even yourself, sometimes. Crash or throw an exception or otherwise fail? Now you've got a potential DOS. There's no way for a parser to win here, in any langauge. The code using the parser has some decisions to make.

Another example, the streaming JSON decoder "accepts" trailing garbage data because by the act of using the streaming JSON decoder you have indicated a willingness to potentially decode more JSON data. You can use this to handle newline-separated JSON, or other interesting JSON protocols where you're not committing to the string being just one JSON value and absolutely nothing else. It's not "an issue they're not planning on fixing", it's a feature with an absolutely unavoidable side effect in the context of streams. The JSON parser stops reading the stream at the end of the complete JSON object, by design, and anything else would be wrong because it would be consuming a value to "check" whether the next thing is JSON or not, when you may not even be "claiming" that the "next thing" is JSON, and whatever input it consumed to verify a claim that nobody is even making would itself be a bug.

Accepting user input into sensitive variables is a common mistake I've seen multiple times in a number of langauges. The root problem there is more the tension between convenience and security than languages themselves; any language can make it so convenient to load data that developers accidentally load more data than they realize.

Etc. The best lesson to take away from this is that there is more than meets the eye with JSON and XML and they're harder to use safely than its ease-of-use suggests.

Although in the interests of fairness I also consider case insensitivity in the JSON field names to be a mistake; maybe it should be an option, JSON can get messy in the real world, but it's a bad default. I have other quibbles but most of them are things where there isn't a correct answer where you can unambiguously say that some choice is wrong. JSON is really quite fundamentally messier than people realize, and XML, while generally more tightly specified at the grammer level than JSON is, is generally quite messy in the protocols people build on top of it.