CVE-2026-55107
kobako Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)
A guest mruby script running inside the Kobako sandbox can execute arbitrary Ruby in the host process, fully escaping the sandbox.
- elct9620 kobako
- Critical
- CVSS 10.0
- EPSS 0.8%
- Fixed version listed
What to do
Fixed version listed
Affected products
| Product | Affected | Fixed in |
|---|---|---|
| elct9620 kobako | >= 0.1.0, < 0.9.1 | None listed |
Affected packages
| Package | Affected | Fixed in | Advisory |
|---|---|---|---|
| kobako (RubyGems) | >= 0.1.0, <= 0.9.0 | 0.9.1 | GHSA-7pwq-q9jf-539h |
Advisories and fixes
- Public exploit github.com
Scores and signals
- Exploitation
- No known exploitation
- Severity
- Critical, CVSS 10.0 (v3.1, scored by GitHub)
- EPSS
- 0.8% chance of exploitation in the next 30 days (EPSS from FIRST, as of Oct 26, 2026)
- CISA's SSVC decision points
- Exploitation: proof of concept. Automatable: yes. Technical impact: total. As of Sep 30, 2026.
- Weakness
- CWE-94: Improper Control of Generation of Code ('Code Injection'); CWE-470: Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')
- Vendor
- elct9620, kobako
Timeline
- First listed as critical by cve.now. Affected and fixed versions come from the CVE record, once one is published.
- GitHub published advisory GHSA-7pwq-q9jf-539h (critical). Fixed in 0.9.1.