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

{
  "id": "6dcef444c81aeca701ad6a57448dc2440aa694f3a375498d036ca284a2069381",
  "url": "https://osv.dev/vulnerability/GHSA-7pwq-q9jf-539h",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "kobako Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)",
    "summary": "### Summary A guest mruby script running inside the Kobako sandbox can execute arbitrary Ruby in the host process, fully escaping the sandbox. ### Details A host embeds bound \"Service\" objects that guest scripts call across the wasm boundary through the transport dispatcher. The dispatcher passed the guest-supplied method name straight to `Object#public_send` on the bound object, with no restriction to the object's own methods: ```ruby target.public_send(method.to_sym, *args, **kwargs, &block) ``` `public_send` can invoke any public method, including Ruby's ambient reflection surface. A guest pivots through the public `send` into otherwise private Kernel methods: a dispatch request with `method = \"send\"` and `args = [:eval, \"\"]` evaluates to `target.send(:eval, \"\")`, running attacker-controlled Ruby in the host. Any bound Service object is sufficient — no Service-specific behavior is required. ### Proof of Concept A guest call equivalent to: ``` Service.send(:eval, \"\") ``` executes in the host process and can read or modify host state, spawn processes, and so on. ### Impact Complete sandbox escape leading to remote code execution in the host process, defeating the gem's central guarantee of isolating untrusted mruby scripts. Any deployment that runs untrusted or attacker-influenced scripts is affected. All released versions (0.1.0 through 0.9.0) are vulnerable; the dispatcher carried the same unguarded `public_send` sink under three successive names (`registry` → `rpc` → `tra",
    "evidence": "osv:GHSA-7pwq-q9jf-539h",
    "products": [
      {
        "name": {
          "value": "kobako",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "0.9.1",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": [
          {
            "value": "0.1.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "0.1.1",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "0.1.2",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "0.2.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "0.2.1",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "0.3.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "0.4.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "0.5.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "0.6.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "0.6.1",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "0.6.2",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "0.7.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "0.8.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "0.9.0",
            "evidence": "/affected/0/versions"
          }
        ]
      }
    ],
    "severity": "critical",
    "structured": {
      "id": "GHSA-7pwq-q9jf-539h",
      "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": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "0.1.0"
                },
                {
                  "fixed": "0.9.1"
                }
              ]
            }
          ],
          "package": {
            "name": "kobako",
            "purl": "pkg:gem/kobako",
            "ecosystem": "RubyGems"
          },
          "versions": [
            "0.1.0",
            "0.1.1",
            "0.1.2",
            "0.2.0",
            "0.2.1",
            "0.3.0",
            "0.4.0",
            "0.5.0",
            "0.6.0",
            "0.6.1",
            "0.6.2",
            "0.7.0",
            "0.8.0",
            "0.9.0"
          ],
          "database_specific": {
            "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-7pwq-q9jf-539h/GHSA-7pwq-q9jf-539h.json",
            "last_known_affected_version_range": "<= 0.9.0"
          }
        }
      ],
      "modified": "2026-10-26T15:00:05.215156345Z",
      "provider": "osv",
      "references": [
        "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",
        "https://github.com/elct9620/kobako",
        "https://github.com/elct9620/kobako/releases/tag/v0.9.1",
        "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/kobako/GHSA-7pwq-q9jf-539h.yml"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-470",
          "CWE-94"
        ],
        "severity": "CRITICAL",
        "github_reviewed": true,
        "nvd_published_at": "2026-09-30T18:18:37Z",
        "github_reviewed_at": "2026-08-18T20:09:59Z"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-55107",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/database_specific/severity"
  },
  "source_id": "core-osv",
  "document_id": 454248,
  "published_at": "2026-08-18T20:09:59+00:00"
}