{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 0.9.0"
      },
      "package": {
        "ecosystem": "RubyGems",
        "name": "kobako"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.1.0"
            },
            {
              "fixed": "0.9.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-55107"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-470",
      "CWE-94"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-08-18T20:09:59Z",
    "nvd_published_at": null,
    "severity": "CRITICAL"
  },
  "details": "### Summary\nA guest mruby script running inside the Kobako sandbox can execute arbitrary\nRuby in the host process, fully escaping the sandbox.\n\n### Details\nA host embeds bound \"Service\" objects that guest scripts call across the wasm\nboundary through the transport dispatcher. The dispatcher passed the\nguest-supplied method name straight to `Object#public_send` on the bound\nobject, with no restriction to the object\u0027s own methods:\n\n```ruby\ntarget.public_send(method.to_sym, *args, **kwargs, \u0026block)\n```\n\n`public_send` can invoke any public method, including Ruby\u0027s ambient\nreflection surface. A guest pivots through the public `send` into otherwise\nprivate Kernel methods: a dispatch request with `method = \"send\"` and\n`args = [:eval, \"\u003cruby\u003e\"]` evaluates to `target.send(:eval, \"\u003cruby\u003e\")`,\nrunning attacker-controlled Ruby in the host. Any bound Service object is\nsufficient \u2014 no Service-specific behavior is required.\n\n### Proof of Concept\nA guest call equivalent to:\n\n```\nService.send(:eval, \"\u003carbitrary host ruby\u003e\")\n```\n\nexecutes in the host process and can read or modify host state, spawn\nprocesses, and so on.\n\n### Impact\nComplete sandbox escape leading to remote code execution in the host process,\ndefeating the gem\u0027s central guarantee of isolating untrusted mruby scripts.\nAny deployment that runs untrusted or attacker-influenced scripts is affected.\nAll released versions (0.1.0 through 0.9.0) are vulnerable; the dispatcher\ncarried the same unguarded `public_send` sink under three successive names\n(`registry` \u2192 `rpc` \u2192 `transport`).\n\n### Patches\nFixed in 0.9.1. The dispatcher now rejects any method whose resolved owner is\na core/meta module (`BasicObject`, `Kernel`, `Object`, `Module`, `Class`), so\nonly methods the bound object itself defines \u2014 or dynamically handles via\n`method_missing` \u2014 remain reachable. The ambient reflection methods (`send`,\n`__send__`, `public_send`, `instance_eval`, `instance_exec`, `method`,\n`instance_variable_get`, \u2026) are all owned by those modules and are blocked.\n\n### Workarounds\nNone within the affected versions. Until you can upgrade, do not bind any\nhost Service object into a sandbox that runs untrusted scripts. Upgrade to\n0.9.1.\n\n### References\n- GHSA-7pwq-q9jf-539h\n- Fix commit: 64f8470\n\n### Credits\nReported and fixed by Ahmed Al Hafoudh.",
  "id": "GHSA-7pwq-q9jf-539h",
  "modified": "2026-08-18T20:09:59Z",
  "published": "2026-08-18T20:09:59Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/elct9620/kobako/security/advisories/GHSA-7pwq-q9jf-539h"
    },
    {
      "type": "WEB",
      "url": "https://github.com/elct9620/kobako/commit/64f84700c81f44902bed9211318d5362f44987b3"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/elct9620/kobako"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "kobako Sandbox Escape: guest eval reaches host RCE via method_missing \u2192 public_send (any bound Service)"
}