> It just takes one crack in the armor,

This is incorrect. It's actually the whole point. Imagine you're an attacker in a gvisor container with a Firecracker hypervisor around you, and a proxy on the host holds a signing secret that gets exposed through the VM virtual device.

Getting access to that secret is not one crack. You need to escalate out of gvisor. That likely gets you control over the Sentry process - let's ignore its sandboxing and just say "you're an unprivileged user".

Any viable attack on Firecracker requires either KVM / hardware exploits (>$1M but definitely real) or has to start at the kernel. Okay, that's about 10-50k to get a kernel LPE, maybe 5K in tokens these days.

So you're in the kernel in the guest of the VM. Time to expoit firecracker lol. It's... never been done. There are like two promising CVEs ever and they're not actually exploitable, no one has done it. Okay, so like, hand waving, let's say it's about $1M to exploit firecracker.

Great, you're unprivileged on the guest. We'll just kind of ignore the additional sandboxing that Firecracker does.

NOW you can try to attack the proxy by scraping its memory or whatever.

This is literally millions of dollars for standard infrastructure hardening and you could go so much further. You can trivially make kernel exploitaton 10x harder, you can make gvisor escapes much much harder, you can move the proxy signing into a TPM (depending on requirements but whatever), you can move the proxy to another computer altogether, you could fuzz these systems for days or run agents against them or whatever.

But one thing is certain - it is never "one crack".