CVE-2026-55107: ELCT9620 Kobako

Critical severity, CVSS 10.0. EPSS: 0.8% chance of exploitation in the next 30 days.

Kobako is a Ruby gem that embeds a Wasm-isolated mruby interpreter inside applications, allowing execution of untrusted Ruby scripts (LLM-generated code, user formulas, student submissions, third-party plugins) in-process without giving them access to host memory, files, network, or credentials. From version 0.1.0 to before version 0.9.1, a guest mruby script running inside the Kobako sandbox can execute arbitrary Ruby in the host process, fully escaping the sandbox. This issue has been patched in version 0.9.1.

Affected products

• ELCT9620 Kobako: from 0.1.0, before 0.9.1 (fixed in 0.9.1)

Published 2026-09-30. Last modified 2026-09-30.