CVE-2026-55107
Kobako Vulnerable to Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)
CRITICAL 10.0
At a glance
- Source
- NVD
- EPSS
- EPSS 0.80 % · percentile 56 ()
- State
- PUBLISHED
- Published
- Updated
- Assigner
- GitHub_M
- NVD status
- Deferred
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.
Weaknesses (CWE)
- CWE-94 — Improper Control of Generation of Code
- CWE-470 — Use of Externally-Controlled Input to Select Classes or Code
References
Scores
| Version | Score | Vector | Scored by |
|---|---|---|---|
| CVSS 3.1 | CRITICAL 10.0 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H | GitHub_M |
| CVSS 3.1 | CRITICAL 10.0 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H | NVD · security-advisories@github.com (Secondary) |
Advisories
- GHSA-7pwq-q9jf-539h — kobako Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)
European references
- ENISA EUVD · EUVD-2026-90197
- GCVE · GCVE-0-2026-55107
Affected products
| Product | Versions |
|---|---|
| elct9620 · kobako | affected >= 0.1.0, < 0.9.1 |
Sources
| Source | Licence |
|---|---|
| CVE List (CVEProject cvelistV5) | CVE Program Terms of Use |
| EPSS (FIRST.org) | FIRST — attribution requested |
| ENISA EUVD | ENISA — reproduction authorised, source acknowledged |
| NVD (NIST) via fkie-cad/nvd-json-data-feeds | Public domain — this product uses data from the NVD API but is not endorsed or certified by the NVD |