CVE-2026-55107

Kobako is a Ruby gem that runs untrusted Ruby inside a Wasm-isolated mruby interpreter so guest scripts should not reach host memory, files, network, or credentials. In versions 0.1.0 before 0.9.1, a guest mruby script can break that isolation and execute arbitrary Ruby in the host process. An attacker who can supply a script—LLM-generated code, a user formula, a student submission, or a third-party plugin—gains the host application's privileges and the resources the sandbox was meant to withhold. Any application embedding Kobako in that version range and passing it untrusted input is affected. The flaw is patched in 0.9.1, is not in CISA KEV, and no public proof-of-concept is known.

What to do: Upgrade Kobako to version 0.9.1 or later. Until then, do not feed untrusted input (LLM-generated code, user formulas, student submissions, or third-party plugins) into the sandbox, and review hosts that embedded older versions for unexpected file, network, or credential access.