[dsl]

That is like saying you can't get a virus on your computer because Facebook doesn't allow viruses to be posted to the internet.

Differential parsing is a whole class of security bugs and they matter a lot. Take a look at HTTP Request Smuggling for examples.

Also, I am pretty sure there are more non-web x509 certificates out there than all the "browser trusted CAs" combined have signed. :)

[woodruffw]

To be clear, the differential here occurs because OpenSSL does the wrong thing. Go is correct to fail closed here, and it’s very hard to imagine a setting in which Go failing closed is a relevant security differential.

[briansmith]

Just to be clear, OpenSSL isn't doing the wrong thing, based on the description in the blog post. The specification allows and even requires behavior similar to that.

[briansmith]

If differential parsing of X.509 certificates is a material security concern for something, then that's a bug in that thing.