CVE-2026-55107Kobako Vulnerable to Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)
Updated under an hour ago ()
Does this affect you?
It affects elct9620 kobako. Add what you run to find out whether that includes you.
EPSS puts the chance of exploitation in the next 30 days at 0.80%, higher than 55% of scored CVEs.
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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.
- CVSS
- 10.0 CRITICAL (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
- Weakness (CWE)
- CWE-94, CWE-470
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- 0.80% (percentile 55)
- Assigned by
- GitHub_M
- NVD analysis
- Deferred
- Record last updated
- Sep 30, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
elct9620 kobako elct9620:kobako (from the name) | from 0.1.0, < 0.9.1 | CNA record |
References
- https://github.com/elct9620/kobako/security/advisories/GHSA-7pwq-q9jf-539hx-refsource-confirm
- https://github.com/elct9620/kobako/commit/64f84700c81f44902bed9211318d5362f44987b3x-refsource-misc
- https://github.com/elct9620/kobako/releases/tag/v0.9.1x-refsource-misc
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.