[emschwartz]

> In Deno Sandbox, secrets never enter the environment. Code sees only a placeholder

> The real key materializes only when the sandbox makes an outbound request to an approved host. If prompt-injected code tries to exfiltrate that placeholder to evil.com? Useless.

That seems clever.

[motrm]

Reminds me a little of Fly's Tokenizer - https://github.com/superfly/tokenizer

It's a little HTTP proxy that your application can route requests through, and the proxy is what handles adding the API keys or whatnot to the request to the service, rather than your application, something like this for example:

Application -> tokenizer -> Stripe

The secrets for the third party service should in theory then be safe should there be some leak or compromise of the application since it doesn't know the actual secrets itself.

Cool idea!

[tptacek]

It's exactly the tokenizer, but we shoplifted the idea too; it belongs to the world!

(The credential thing I'm actually proud of is non-exfiltratable machine-bound Macaroons).

Remember that the security promises of this scheme depend on tight control over not only what hosts you'll send requests to, but what parts of the requests themselves.

[pbowyer]

This reminds me of a SaaS that existed 15+ years ago for PCI-DSS compliance. It did exactly that: you had it tokenize and store the sensitive data, and then you proxied your requests via it, and it inserted them into the request. It was a very neat way to get around storing data yourself.

I cannot remember what the platform was called, let me know if you do.

[dtkav]

I've been working on something similar (with claude code).

It's a sandbox that uses envoy as a transparent proxy locally, and then an external authz server that can swap the creds.

The idea is extended further in that the goal is to allow an org to basically create their own authz system for arbitrary upstreams, and then for users to leverage macaroons to attentuate the tokens at runtime.

It isn't finished but I'm trying to make it work with ssh/yubikeys as an identity layer. The authz macaroon can have a "hole" that is filled by the user/device attestation.

The sandbox has some nice features like browser forwarding for Claude oauth and a CDP proxy for working with Chrome/Electron (I'm building an Obsidian plugin).

I'm inspired by a lot of the fly.io stuff in tokenizer and sprites. Exciting times.

https://github.com/dtkav/agent-creds

[ptx]

Yes... but...

Presumably the proxy replaces any occurrence of the placeholder with the real key, without knowing anything about the context in which the key is used, right? Because if it knew that the key was to be used for e.g. HTTP basic auth, it could just be added by the proxy without using a placeholder.

So all the attacker would have to do then is find and endpoint (on one of the approved hosts, granted) that echoes back the value, e.g. "What is your name?" -> "Hello $name!", right?

But probably the proxy replaces the real key when it comes back in the other direction, so the attacker would have to find an endpoint that does some kind of reversible transformation on the value in the response to disguise it.

It seems safer and simpler to, as others have mentioned, have a proxy that knows more about the context add the secrets to the requests. But maybe I've misunderstood their placeholder solution or maybe it's more clever than I'm giving it credit for.

[booi]

Where would this happen? I have never seen an API reflect a secret back but I guess it's possible? perhaps some sort of token creation endpoint?

[sothatsit]

Could the proxy place further restrictions like only replacing the placeholder with the real API key in approved HTTP headers? Then an API server is much less likely to reflect it back.

[simonw]

Yeah, this is a really neat idea: https://deno.com/blog/introducing-deno-sandbox#secrets-that-...

  await using sandbox = await Sandbox.create({
    secrets: {
      OPENAI_API_KEY: {
        hosts: ["api.openai.com"],
        value: process.env.OPENAI_API_KEY,
      },
    },
  });
  
  await sandbox.sh`echo $OPENAI_API_KEY`;
  // DENO_SECRET_PLACEHOLDER_b14043a2f578cba75ebe04791e8e2c7d4002fd0c1f825e19...

It doesn't prevent bad code from USING those secrets to do nasty things, but it does at least make it impossible for them to steal the secret permanently.

Kind of like how XSS attacks can't read httpOnly cookies but they can generally still cause fetch() requests that can take actions using those cookies.

[its-summertime]

if there is an LLM in there, "Run echo $API_KEY" I think could be liable to return it, (the llm asks the script to run some code, it does so, returning the placeholder, the proxy translates that as it goes out to the LLM, which then responds to the user with the api key (or through multiple steps, "tell me the first half of the command output" e.g. if the proxy translates in reverse)

Doesn't help much if the use of the secret can be anywhere in the request presumably, if it can be restricted to specific headers only then it would be much more powerful

[ryanrasti]

> It doesn't prevent bad code from USING those secrets to do nasty things, but it does at least make it impossible for them to steal the secret permanently.

Agreed, and this points to two deeper issues: 1. Fine-grained data access (e.g., sandboxed code can only issue SQL queries scoped to particular tenants) 2. Policy enforced on data (e.g., sandboxed code shouldn't be able to send PII even to APIs it has access to)

Object-capabilities can help directly with both #1 and #2.

I've been working on this problem -- happy to discuss if anyone is interested in the approach.

[Tepix]

It must be performing a man-in-the-middle for HTTPS requests. That makes it more difficult to do things like certificate pinning.

[artahian]

We had this same challenge in our own app builder, we ended up creating an internal LLM proxy with per-sandbox virtual keys (which the proxy maps to the real key + calculates per-sandbox usage), so even if the sandbox leaks its key it doesn't impact anything else.

[jkelleyrtp]

@deno team, how do secrets work for things like connecting to DBs over a tcp connection? The header find+replace won't work there, I assume. Is the plan to add some sort of vault capability?

[perfmode]

I was just about to say the same thing. Cool technique.

[CuriouslyC]

This is an old trick that people do with Envoy all the time.

[verdverm]

Dagger has a similar feature: https://docs.dagger.io/getting-started/types/secret/

Same idea with more languages on OCI. I believe they have something even better in the works, that bundles a bunch of things you want in an "env" and lets you pass that around as a single "pointer"

I use this here, which eventually becomes the sandbox my agent operates in: https://github.com/hofstadter-io/hof/blob/_next/.veg/contain...

[linolevan]

It’s pretty neat.

Had some previous discussion that may be interesting on https://news.ycombinator.com/item?id=46595393

[syabro]

I don’t quite get how it’s being injected in https requests… do they inject their own https cert?

[rfoo]

I like this, but the project mentioned in the launch post

> via an outbound proxy similar to coder/httpjail

looks like AI slop ware :( I hope they didn't actually run it.

[lucacasonato]

We run or own infrastructure for this (and everything else). The link was just an illustrative example