[altair]

You could no more bring down a network with ASN.1 than you could a UNIX system with a bootleg copy of yacc.

Bad example. This has been done before, only with the C compiler not yacc.

[eno_]

I'm old enough to have been writing UNIX device drivers for a living when Ken Thompson's C compiler 'sploit was first discussed. That is an example of is why even source-code-audited systems are not totally immune to back doors. You have to audit the code the compiler generates, and there may even be theoretical limits on how comprehensively that can be done.

But the effectiveness of this kind of 'sploit, like every other kind, is limited by the diversity of implementations out there. There is no mother of all protocol compilers that could have been infected with a trojan, and that one could use to bring down all networks. Nor is there any other one-size-fits-all exploit, nor even a manageable collection of them that any group short of an NSA or GCHQ type government agency could possibly make any practical use of.