{"id":"CVE-2026-55107","aliases":["EUVD-2026-90197","GHSA-7pwq-q9jf-539h"],"status":"published","title":"Kobako Vulnerable to Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)","description":"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.","severity":{"version":"3.1","score":10,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H","level":"critical","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00799,"percentile":0.56866,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-470","CWE-94"],"published":"2026-08-18T20:09:59Z","modified":"2026-10-28T02:30:36Z","fixes":[{"ecosystem":"RubyGems","package":"kobako","fixed_in":["0.9.1"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"RubyGems","package":"kobako","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0.1.0"},{"last_affected":"0.9.0"},{"fixed":"0.9.1"}]}]},{"source":"osv","ecosystem":"RubyGems","package":"kobako","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0.1.0"},{"fixed":"0.9.1"}]}],"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"]}],"products":[{"vendor":"elct9620","product":"kobako"}],"references":[{"url":"https://github.com/elct9620/kobako/security/advisories/GHSA-7pwq-q9jf-539h","tags":["x_refsource_CONFIRM","exploit","advisory","web"]},{"url":"https://github.com/elct9620/kobako/commit/64f84700c81f44902bed9211318d5362f44987b3","tags":["x_refsource_MISC","fix","web"]},{"url":"https://github.com/elct9620/kobako/releases/tag/v0.9.1","tags":["x_refsource_MISC","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-55107","tags":["advisory"]},{"url":"https://github.com/rubysec/ruby-advisory-db/blob/master/gems/kobako/GHSA-7pwq-q9jf-539h.yml","tags":["web"]},{"url":"https://github.com/advisories/GHSA-7pwq-q9jf-539h"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55107.json","tags":["advisory"]},{"url":"https://github.com/elct9620/kobako","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-55107","title":"Kobako Vulnerable to Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)","description":"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.","status":"published","published":"2026-09-30T17:06:00.286Z","modified":"2026-09-30T19:49:04.193Z","cvss":[{"version":"3.1","score":10,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H","level":"critical","assessor":"cna"}],"cwes":["CWE-94","CWE-470"],"updated_at":"2026-11-02T14:20:12.260247Z"}],"euvd":[{"id":"EUVD-2026-90197","description":"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.","status":"published","published":"2026-09-30T17:06:00Z","modified":"2026-09-30T19:49:04Z","cvss":[{"version":"3.1","score":10,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H","level":"critical"}],"updated_at":"2026-11-02T17:27:47.293232Z"}],"ghsa":[{"id":"GHSA-7pwq-q9jf-539h","title":"kobako Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)","description":"### 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, \u0026block)\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, \"\u003cruby\u003e\"]` evaluates to `target.send(:eval, \"\u003cruby\u003e\")`,\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, \"\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'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.","status":"published","published":"2026-08-18T20:09:59Z","modified":"2026-10-26T14:45:09Z","cvss":[{"version":"3.1","score":10,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H","level":"critical"}],"cwes":["CWE-94","CWE-470"],"updated_at":"2026-11-02T14:41:36.858527Z"}],"nvd":[{"id":"CVE-2026-55107","description":"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.","status":"published","published":"2026-09-30T18:18:37.55Z","modified":"2026-09-30T20:17:32.923Z","cvss":[{"version":"3.1","score":10,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H","level":"critical","assessor":"secondary"}],"cwes":["CWE-94","CWE-470"],"updated_at":"2026-11-02T14:12:53.097633Z"}],"osv":[{"id":"CVE-2026-55107","title":"Kobako Vulnerable to Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)","description":"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.","status":"published","published":"2026-09-30T17:06:00.286Z","modified":"2026-10-28T02:30:36.29280559Z","cvss":[{"version":"3.1","score":10,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H","level":"critical"}],"cwes":["CWE-470","CWE-94"],"updated_at":"2026-11-02T15:45:11.22012Z"},{"id":"GHSA-7pwq-q9jf-539h","title":"kobako Sandbox Escape: guest eval reaches host RCE via method_missing → public_send (any bound Service)","description":"### 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, \u0026block)\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, \"\u003cruby\u003e\"]` evaluates to `target.send(:eval, \"\u003cruby\u003e\")`,\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, \"\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'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.","status":"published","published":"2026-08-18T20:09:59Z","modified":"2026-10-26T15:00:05.215156345Z","cvss":[{"version":"3.1","score":10,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H","level":"critical"}],"cwes":["CWE-470","CWE-94"],"updated_at":"2026-11-02T15:46:41.349637Z"}]}}