[simias]

That's not UB, that's implementation dependent, AFAIK the C standard says nothing about read-only memory. Attempting to modify a string literal is indeed UB but that would only happen if an attacker managed to attempt to modify the string, not when the program is used normally.

[shakna]

> That's not UB, that's implementation dependent, AFAIK the C standard says nothing about read-only memory.

If we're being pedantic, it's _unspecified behaviour_. The implementation isn't required to document how it would behave.

[shawnz]

Other important security features like N^X are also not specified in the C standard either, so what's the point of worrying about just printf format strings?

[ryandrake]

TBH it’s not pedantic to understand the difference between undefined, implementation-defined, and unspecified behavior. It’s part of knowing the language. One of my standard interview questions for C candidates is to ask them to describe and provide an example of each.

[Dylan16807]

Is there really a meaningful difference between implementation-defined and unspecified? I'd say they're shades of gray based on how pedantic the compiler documentation is.

[temac]

Is it really not UB to attempt to modify RO things? Typically (on major implementations, e.g. GNU/Linux or MSVC/Windows) it will crash, and I don't think it is allowed to crash on non-UB things?