I've heard this sentiment a lot, that governments/secret agencies/whoever create zero-days intentionally, for their own use.
This is an interesting thought to me (like, how does one create a zero-day that doesn't look intentional?) but the more I think about it, the more I start to believe that this fully is not necessary. There are enough faulty humans and memory unsafe languages in the loop that there will always be a zero-day somewhere, you just need to find it.
(this isn't to say something like the NSA has never created or ordered the creation of a backdoor - I just don't think it would be in the form of an "unintentional" zero-day exploit)
I'm not sure that governments actually create them, not prolifically at least. There's been some state actor influence over the years, for sure.
However, exploits that are known (only) by a state actor would most definitely be a closely guarded secret. It's only convenient for a state to release information about an exploit when either it's been made public or it has more consequences for not releasing.
So yes, exactly what you said. It's easier to find the exploits than to create them yourself. By extrapolation, you would have to assume that each state maintains its set of secret exploits, possibly never getting to use them for fear of the other side knowing of their existence. Cat & Mouse, Spy vs Spy for sure.
>In December 2013, a Reuters news article alleged that in 2004, before NIST standardized Dual_EC_DRBG, NSA paid RSA Security $10 million in a secret deal to use Dual_EC_DRBG as the default in the RSA BSAFE cryptography library
https://en.wikipedia.org/wiki/Dual_EC_DRBG
I think you are right that the shady actors pretty much can use existing bugs.
But you are also right that this is not the only way they work. With the XZ Utils backdoor (2024), we normal nerds got an interesting glimpse into how they create a zero-day. It was luckily discovered by an american developer not looking for zero-days, just debugging a performance problem.
