undefined | Better HN

0 pointsneonsunset1y ago0 comments

There aren't in C#. Neither Newtonsoft.JSON (by default) nor System.Text.Json (at all) allow uncontrolled deserialization. Pretty much no code ever defaulted to Newtonsoft's TypeNameHandling.Auto and community has always been aware of its dangers, espcially in light of the incidents like Log4J.

And BinaryFormatter has been long ago deprecated (and now it got completely removed, in the form of a breaking change, something that pretty much never happens otherwise), and even when it was in use (more than a decade ago, popularity-wise), the use of type binding was heavily encouraged.

0 comments

ethbr11y ago

C# is pretty hard-nosed about serialization.

E.g. My discovery the other day that out of the box C# System.Text.Json can't serialize System.Exception without writing a custom serializer [0] (since 2020, because .NET fix speed...). NewtonSoft handles it fine. (Had wanted a quick-and-dirty debugging dump of properties)

[0] https://github.com/dotnet/runtime/issues/43026

neonsunsetOP1y ago

A serializer cannot make a reasonable assumption about how an exception should be serialized on the user's behalf, let alone deserialized. Newtonsoft had and still has quite a few problematic defaults where people can inadvertently weaken privacy and security of the implementation, which System.Text.Json is opinionated in solving.

If you are okay with risks that come from including exception's message in data sent over the network (e.g. not publicly exposed), then defining a custom converter is trivial (it's like 10-15 lines and adding it to serializer options), or you could simply .ToString/.Message it and include that in the payload instead. It's a minute thing.

As for exception deserialization, that's a gross feature misuse and not something that should be done.

ethbr11y ago

To me, it feels like an abuse of "you shouldn't be doing that"-ism.

A serializer should generate a sane serialization of whatever I throw at it. Or at least have an option that allows me to force that.

If I then choose to send that serialization somewhere unreasonable, that's on me.

In my case, I was hacking in C#-on-top-of-another-environment, so didn't have full access to reimplement stuff, without jumping through additional hoops.

That said, absolutely agreed on de-serialization, as larger opportunities for footguns abound.

lyu072821y ago

I was thinking of BinaryFormatter and NetDataContractSerializer, etc. unsafe .NET object deserialization. I'm sure the default JSON serializer in C# is safe (lmao language fanboys)

https://github.com/pwntester/ysoserial.net

j / k navigate · click thread line to collapse

0 pointsneonsunset1y ago0 comments

0 comments

ethbr11y ago

C# is pretty hard-nosed about serialization.

[0] https://github.com/dotnet/runtime/issues/43026

neonsunsetOP1y ago

As for exception deserialization, that's a gross feature misuse and not something that should be done.

ethbr11y ago

To me, it feels like an abuse of "you shouldn't be doing that"-ism.

A serializer should generate a sane serialization of whatever I throw at it. Or at least have an option that allows me to force that.

If I then choose to send that serialization somewhere unreasonable, that's on me.

In my case, I was hacking in C#-on-top-of-another-environment, so didn't have full access to reimplement stuff, without jumping through additional hoops.

That said, absolutely agreed on de-serialization, as larger opportunities for footguns abound.

lyu072821y ago

I was thinking of BinaryFormatter and NetDataContractSerializer, etc. unsafe .NET object deserialization. I'm sure the default JSON serializer in C# is safe (lmao language fanboys)

https://github.com/pwntester/ysoserial.net

j / k navigate · click thread line to collapse