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

{
  "id": "4642fa2baabdfbfcd821fcf4118235779900c5d96f534882cb150b6b62f47e83",
  "url": "https://osv.dev/vulnerability/CVE-2026-55107",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Kobako Vulnerable to Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)",
    "summary": "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.",
    "evidence": "osv:CVE-2026-55107",
    "products": [],
    "severity": "critical",
    "structured": {
      "id": "CVE-2026-55107",
      "aliases": [
        "CVE-2026-55107",
        "GHSA-7pwq-q9jf-539h"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/elct9620/kobako",
              "type": "GIT",
              "events": [
                {
                  "introduced": "631ddc7f04bf34b39e5eb66520e1692240f8f231"
                },
                {
                  "fixed": "98e854d2cff111bd7a8c7760d95b6f4cad6c4af8"
                },
                {
                  "fixed": "64f84700c81f44902bed9211318d5362f44987b3"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0.1.0"
                      },
                      {
                        "fixed": "0.9.1"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "64f84700c81f44902bed9211318d5362f44987b3"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "98e854d2cff111bd7a8c7760d95b6f4cad6c4af8"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v0.9.1"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v0.9.0",
            "kobako-rs-v0.4.0",
            "kobako-regexp-v0.4.0",
            "kobako-io-v0.4.0",
            "kobako-core-v0.4.0",
            "kobako-rs-v0.3.0",
            "kobako-io-v0.3.0",
            "kobako-core-v0.3.0",
            "v0.8.0",
            "kobako-core-v0.2.0",
            "v0.7.0",
            "v0.6.2",
            "v0.6.1",
            "v0.6.0",
            "v0.5.0",
            "v0.4.0",
            "v0.3.0",
            "v0.2.1",
            "v0.2.0",
            "v0.1.2",
            "v0.1.1",
            "v0.1.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-55107.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:36.292805590Z",
      "provider": "osv",
      "references": [
        "https://github.com/elct9620/kobako/releases/tag/v0.9.1",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55107.json",
        "https://github.com/elct9620/kobako/security/advisories/GHSA-7pwq-q9jf-539h",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-55107",
        "https://github.com/elct9620/kobako/commit/64f84700c81f44902bed9211318d5362f44987b3"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-470",
          "CWE-94"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55107.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-55107",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 503377,
  "published_at": "2026-09-30T17:06:00.286+00:00"
}