critical

CVE-2026-55107

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

Published 30 Sep 2026Modified 30 Sep 2026CWE 94, 470

In the Trivy database since at least 24 Oct 2026, 07:11 UTCWhen it arrived before that build is not recorded.

Severity by source

GHSA10.0CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Trivy's own label is CRITICAL. Rated critical by GHSA, Ruby Advisory DB.

Description

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 packages and fixed versions

Source	Package	Fixed in
rubygems::GitHub Security Advisory RubyGems	kobako	0.9.1
rubygems::Ruby Advisory Database	kobako	>= 0.9.1

References

All 11 references

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