Updated advisory posts against rubysec/ruby-advisory-db@2faad0c

Author: jasnow

advisories/_posts/2026-08-18-CVE-2026-55107.md

@@ -0,0 +1,57 @@
+---
+layout: advisory
+title: 'CVE-2026-55107 (kobako): kobako Sandbox Escape - guest eval reaches host RCE
+  via method_missing → public_send (any bound Service)'
+comments: false
+categories:
+- kobako
+advisory:
+  gem: kobako
+  cve: 2026-55107
+  ghsa: 7pwq-q9jf-539h
+  url: https://github.com/elct9620/kobako/security/advisories/GHSA-7pwq-q9jf-539h
+  title: kobako Sandbox Escape - guest eval reaches host RCE via method_missing →
+    public_send (any bound Service)
+  date: 2026-08-18
+  description: |-
+    ### Summary
+
+    A guest mruby script running inside the Kobako sandbox can execute
+    arbitrary Ruby in the host process, fully escaping the sandbox.
+
+    ### 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` → `transport`).
+
+    ### Credits
+
+    Reported and fixed by Ahmed Al Hafoudh.
+  cvss_v3: 10.0
+  patched_versions:
+  - ">= 0.9.1"
+  related:
+    url:
+    - https://rubygems.org/gems/kobako/versions/0.9.1
+    - https://github.com/elct9620/kobako/blob/main/CHANGELOG.md#091-2026-06-11
+    - https://github.com/elct9620/kobako/commit/dd081665f368f7ba54e476c3ad045ee1aa8ed703
+    - https://github.com/elct9620/kobako/commit/64f84700c81f44902bed9211318d5362f44987b3
+    - https://advisories.gitlab.com/gem/kobako/CVE-2026-55107
+    - https://github.com/elct9620/kobako/security/advisories/GHSA-7pwq-q9jf-539h
+    - https://github.com/advisories/GHSA-7pwq-q9jf-539h
+  notes: |
+    - cvss_v3 from GHSA
+    - CVE is reserved, but not published.
+    - Details on Patch:
+      - Fixed in 0.9.1. The dispatcher now rejects any method whose resolved
+        owner is a core/meta module (`BasicObject`, `Kernel`, `Object`,
+        `Module`, `Class`), so only methods the bound object itself defines —
+        or dynamically handles via `method_missing` — remain reachable.
+        The ambient reflection methods (`send`, `__send__`, `public_send`,
+        `instance_eval`, `instance_exec`, `method`, `instance_variable_get`,
+        …) are all owned by those modules and are blocked.
+---