by Kastro
Paper/Archive/CVE-2026-55107

CVE-2026-55107

elct9620 kobako — Kobako Vulnerable to Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)

EPSS 0.8%public exploitCVSS 10.0
critical.is priorityof 100
51
CVSS 10.0 (CNA)10.0 / 10 × 3030.0Not in CISA KEV+300.0EPSS percentile 56.5.565 × 2011.3Exploit: SSVC poc+1010.0SSVC exploitation: poc+100.0
Description · from the CVE record

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.

Affected

ProductAffectedFixed inSource
kobako>= 0.1.0, < 0.9.1–CNA

Scores by source

GitHub_M (CNA)10.0CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
CISA ADPSSVCExploitation: poc · Automatable: yes · Technical impact: total

References

exploitgithub.com/elct9620/kobako/security/advisories/GHSA-7pwq-q9jf-539hrefgithub.com/elct9620/kobako/commit/64f84700c81f44902bed9211318d5362f44987b3refgithub.com/elct9620/kobako/releases/tag/v0.9.1