Hi Timo,
I don’t do C anymore but here’s running Rust code of a full DKIM2 implementation. Please do try to break it:
Best, Mauro
Hi Mauro,hi all,Yes Mauro, Streaming JSON would be possible, if it were a stream,but it is encapsulated. When I hear SAX, I need to think aboutmusic.BTW: Hannah also said "That's not nice, that's DoS. [...] Changethe spec to forbid additional items in the top-level JSONObject. ", think about it.Mauro, if you think, that the actual design has no flaws,provide running C code.Best,TimoIt looks like Mauro De Gennaro aimed to say:Hi Timo,
Every conclusion in your message rests on assumptions about how a particular parser happens to be implemented.
MIME is not linear by nature. It is a nested format: multipart containers can hold further multipart containers, and message/rfc822 parts can embed entire messages. A parser that recurses on that structure can be driven to stack exhaustion by a deeply nested message, and this has happened in real products. "Streaming and linear" describes a well-written MIME parser, not MIME itself.
The same reasoning applies to JSON. JSON encapsulated in JSON does not require building a DOM. Streaming, event-based parsers have existed for many years and process input incrementally with bounded memory, including for long flat arrays. Whether an implementation builds a tree, recurses, or streams is a design decision by the library author, not a property of the format.
The picture you describe is also outdated and does not match how modern libraries are written. Current parsers commonly enforce configurable limits on nesting depth, input size, and allocation, and they fail cleanly when those limits are hit. A crafted envelope causing an immediate process collapse describes a naive or unmaintained implementation, not the state of the art.
The only vulnerability in this scenario is the use of a flawed library, and a specification cannot repair a flawed library. An implementer who picks a parser that cannot safely handle untrusted input will have the same problem with MIME, JSON, or any other format. I would ask that we not present this as a structural weakness of the DKIM2 design, because the argument does not hold up.
Best,
Mauro
Timo GerkeHamburg, Germany"If you think technology can solve your security problems then you don't understand the problems and you don't understand the technology." -- Bruce Schneier<OpenPGP_0x9F03DF9F597BF31E.asc> _______________________________________________
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