---
id: CVE-2026-55107
title: >-
  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 …
summary: >-
  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 …
severity: critical
cvss: 10
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H'
cwe:
  - CWE-94
  - CWE-470
vendor: elct9620
product: kobako
affected:
  - 'kobako >= 0.1.0, < 0.9.1'
patched:
  - kobako 0.9.1
published: '2026-09-30'
updated: '2026-09-30'
sourceUpdated: '2026-09-30T20:17:32.923'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-55107'
references:
  - url: >-
      https://github.com/elct9620/kobako/commit/64f84700c81f44902bed9211318d5362f44987b3
    label: security-advisories@github.com
  - url: 'https://github.com/elct9620/kobako/releases/tag/v0.9.1'
    label: security-advisories@github.com
  - url: 'https://github.com/elct9620/kobako/security/advisories/GHSA-7pwq-q9jf-539h'
    label: security-advisories@github.com
  - url: 'https://github.com/elct9620/kobako/security/advisories/GHSA-7pwq-q9jf-539h'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: 'https://github.com/advisories/GHSA-7pwq-q9jf-539h'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-55107'
  - url: >-
      https://github.com/rubysec/ruby-advisory-db/blob/master/gems/kobako/GHSA-7pwq-q9jf-539h.yml
tags:
  - nvd
  - cve.org
  - exploit-available
  - ghsa
  - rubygems
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'yes'
  technicalImpact: total
  timestamp: '2026-09-30T19:48:55.982496Z'
aliases:
  - GHSA-7pwq-q9jf-539h
ecosystem: rubygems
ingestedAt: '2026-08-18T20:22:15.701Z'
epss: 0.00799
epssPercentile: 0.56352
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-55107)

Affected packages:

- `kobako >= 0.1.0, <= 0.9.0`

Patched in:

- `kobako 0.9.1`

Source: https://github.com/advisories/GHSA-7pwq-q9jf-539h