That's essentially what NEXT_PUBLIC_ is for... but serializing process.env is a new one for me.

IIRC, react had this issue so they required env vars seen in react to be prefixed by REACT_ The hope being that SECRET is not prefixed and so is not available. Of course it requires you to know why they are prefixed and not make REACT_SECRET

Lifetime is the underlying issue.

For example, it is possible to create a vault lease for exactly one CI build and tie the lifetime of secrets the CI build needs to the lifetime of this build. Practically, this would mean that e.g. a token, some oauth client-id/client-secret or a username/password credential to publish an artifact is only valid while the build runs plus a few seconds. Once the build is done, it's invalidated and deleted, so exfiltration is close to meaningless.

There are two things to note about this though:

This means the secret management has to have access to powerful secrets, which are capable of generating other secrets. So technically we are just moving goal posts from one level to another. That is fine usually though - I have 5 vault clusters to secure, and 5 different CI builds every 10 minutes or so, or couple thousand application instances in prod. I can pay more attention to the vault clusters.

But this is also not easy to implement. It needs a vault cluster, dynamic PostgreSQL users take years to get right, we are discovering how applications can be terrible at handling short-lived certificates every month (and some even regress. Grafana seems to have with PostgreSQL client certs in v11/v12), we've found quite a few applications who never thought that certs with less than a year of lifetime even exists. Oh and if your application is a single-instance monolith, restarting to reload new short-lived DB-certs is also terrible.

Automated, aggressive secret management and revocation imo is a huge problem to many secret exfiltration attacks, but it is hard to do and a lot of software resists it very heavily on many layers.

I'm not sure that's necessarily a "problem", though it is fundamental to secrets. We wouldn't say that it's a fundamental problem that doors on houses need a key--that's what the key is for--the problem is if the key isn't kept secure from unauthorized actors.

Like, sure, you can go HAM here and use network proxy services to do secret decryption, and only talk from the app to those proxies via short-lived tokens; that's arguably a qualitative shift from app-uses-secret-directly, and it has some real benefits (and costs, namely significant complexity/fragility).

Instead, my favored option is to scope secret use to network locations. If, for example, a given NPM token can only be used for API calls issued from the public IP endpoint of the user's infrastructure, that's a significant added layer of security. People don't agree on whether or not this counts as a "token ACL", but it's certainly ACL-like in its functionality--just controlled by location, rather than identity.

This approach can also be adopted gradually and with less added fragility than the proxy-all-the-things approach: token holders can initially allowlist broad or shared network location ranges, and narrow allowed access sources over time as their networks are improved.

Of course, that's a fantasy. API providers would have to support network-scoped API access credentials, and almost none of them do.

Yep. Then you run into the issue of where to store the secret encryption key.

Security researchers always need to give an answer whenever there's a security incident and the answer can never be "too much centralization risk" even when that is the only reasonable answer. You can't remove centralization risk.

IMO, the future is; every major centralized platform will be insecure in perpetuity and nothing can be done about it.

HSMs & similar can at least time-limit access to secrets to the period where an attacker can make requests to the HSM.