CVE-2026-55107

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

State: Published
Severity: 10.0 Critical
Published: Sep 30, 2026
Updated: Sep 30, 2026
Reserved: Jun 16, 2026

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.

Scores

CVSS	Score	Vector	Source
3.1	10.0 Critical	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H	GitHub_M

Weaknesses

CWE-94 Improper Control of Generation of Code ('Code Injection')
CWE-470 Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')

Affected Products

Product	Versions
kobakoelct9620	>= 0.1.0, < 0.9.1Affected

References

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