CVE-2026-55107: kobako Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)

August 18, 2026

A guest mruby script running inside the Kobako sandbox can execute arbitrary Ruby in the host process, fully escaping the sandbox.

References

github.com/advisories/GHSA-7pwq-q9jf-539h
github.com/elct9620/kobako/commit/64f84700c81f44902bed9211318d5362f44987b3
github.com/elct9620/kobako/security/advisories/GHSA-7pwq-q9jf-539h
nvd.nist.gov/vuln/detail/CVE-2026-55107

Code Behaviors & Features

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