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.
Published: 2026-09-30
Score: 10 Critical
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-7pwq-q9jf-539h kobako Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)
History

Wed, 30 Sep 2026 17:30:00 +0000

Type Values Removed Values Added
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.
Title Kobako Vulnerable to Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)
Weaknesses CWE-470
CWE-94
References
Metrics cvssV3_1

{'score': 10, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H'}

Subscriptions

No data.

cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-09-30T17:06:00.286Z

Reserved: 2026-06-16T14:41:54.579Z

Link: CVE-2026-55107

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-30T18:18:37.550

Modified: 2026-09-30T18:18:37.550

Link: CVE-2026-55107

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses
  • CWE-470

    Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')

  • CWE-94

    Improper Control of Generation of Code ('Code Injection')