Vulnerabilities in pkg:gem/kobako

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-7pwq-q9jf-539h",
  "modified" : "2026-08-18T20:09:59Z",
  "published" : "2026-08-18T20:09:59Z",
  "aliases" : [ "CVE-2026-55107" ],
  "summary" : "kobako Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)",
  "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's own methods:\n\n```ruby\ntarget.public_send(method.to_sym, *args, **kwargs, &block)\n```\n\n`public_send` can invoke any public method, including Ruby's 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, \"<ruby>\"]` evaluates to `target.send(:eval, \"<ruby>\")`,\nrunning attacker-controlled Ruby in the host. Any bound Service object is\nsufficient — no Service-specific behavior is required.\n\n### Proof of Concept\nA guest call equivalent to:\n\n```\nService.send(:eval, \"<arbitrary host ruby>\")\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's 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` → `rpc` → `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 — or dynamically handles via\n`method_missing` — remain reachable. The ambient reflection methods (`send`,\n`__send__`, `public_send`, `instance_eval`, `instance_exec`, `method`,\n`instance_variable_get`, …) 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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "kobako"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.1.0"
      }, {
        "fixed" : "0.9.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.9.0"
    }
  } ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-470", "CWE-94" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-18T20:09:59Z",
    "nvd_published_at" : null
  }
}