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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-55107
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-30 18:18:37 UTC
Updated2026-09-30 20:17:32 UTC
DescriptionKobako 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.

Risk And Classification

Primary CVSS: v3.1 10 CRITICAL from [email protected]

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

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

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary10CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
3.1CNADECLARED10CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Elct9620 Kobako affected >= 0.1.0, < 0.9.1 Not specified

References

ReferenceSourceLinkTags
github.com/elct9620/kobako/security/advisories/GHSA-7pwq-q9jf-539h 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
github.com/elct9620/kobako/commit/64f84700c81f44902bed9211318d5362f44987b3 [email protected] github.com
github.com/elct9620/kobako/releases/tag/v0.9.1 [email protected] github.com
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