CVE-2026-55107

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

At a glance

Severity: CRITICAL 10.0
EPSS: EPSS 0.80 % · percentile 56 (2026-10-27)
State: PUBLISHED
Published: 2026-09-30
Updated: 2026-09-30
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.

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)

Weaknesses (CWE)

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

References

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