| Security is a concern for every layer. It's not magic pixie dust that' can be sprinkled on top of software to renders it secure! A while ago I read a great article about how the Adobe PDF serialization format is nearly impossible to secure because it allows inherently unsafe constructs. For example, it allows cross-references that are basically just arbitrary unaligned pointers. It uses many different alignment and padding algorithms. It has length-prefixed and not-length prefixed sections. Etc, etc... Apparently it was a serious research exercise to make a safe PDF parser, and they only covered a fraction of the full spec! To put things in perspective: Originally, PDF allowed arbitrary code execution as a core feature, allowing the output of shell commands to be used as document content. Most people like the Chromium and Firefox teams have just given up and now parse PDF using a sandboxed JavaScript VM because it's too hard to do it safely with C++. They parse HTML and JavaScript with C++, but not PDF. Think about that. A similar issue caused Log4j, where a "format string parser" contained a vulnerability because it was too flexible and allowed network requests to be triggered by user-controlled data. Even trivial, "surely it must be safe" formats like XML and JSON are riddled with security issues, such as different layers in a microservice architecture having different handling semantics for duplicate keys, null values, etc... This can result in exploits such as authentication and authorization tokens being interpreted by a system one way, but a different way by a different system. For real-world attacks along these lines, search for "request smuggling". Serialization and parsing are security minefields and it is dangerously naive to just hand-wave that away. See: https://seriot.ch/projects/parsing_json.html |
when execution of user-supplied code is allowed (in the examples that you have outlined above), surely, the layer _executing_ the code cannot really do anything about it ! perhaps you actually did intend to `rm -rf /` ?
policy checking, enforcement etc. has to happen at a higher / different layer. i am not sure why mechanism and policy are being conflated here.
in the same way, you gave the serialization layer a 10mb or whatever sized input to serialize, sure...you get an valid serialized output etc. maybe there is a genuine usecase for that in some context or another f.e. when serializing say image files, or something else etc. etc.
[edit] : minor comment.