kobako Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)

Summary

A guest mruby script running inside the Kobako sandbox can execute arbitrary

Ruby in the host process, fully escaping the sandbox.

Details

A host embeds bound "Service" objects that guest scripts call across the wasm

boundary through the transport dispatcher. The dispatcher passed the

guest-supplied method name straight to Object#public_send on the bound

object, with no restriction to the object's own methods:

target.public_send(method.to_sym, *args, **kwargs, &block)