{"id":"CVE-2026-88257","revision":null,"records":[{"revision":"e4207e3b12374ec886ea4999e71ac07e","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-88257","aliases":[],"title":"beam_mcp: nested tool argument constraints advertised but not enforced","description":"Improper Input Validation vulnerability in BeamMCP.Schema in ScriptKittyOS beam_mcp allows an MCP client to reach a tool's dispatch function with arguments that violate the input schema the server advertised. BeamMCP.Schema.validate/2 checked type, required, additionalProperties, enum and numeric bounds on the top-level arguments object only. Constraints inside nested objects and on array items (items, minItems, maxItems, minLength, maxLength, pattern, nested required, enum and additionalProperties: false) were advertised by tools/list and never checked at tools/call or prompts/get, and keywords outside the enforced subset (oneOf, anyOf, $ref) were advertised and ignored.\n\nA host whose dispatch code relies on the schema it declared receives values the schema forbids, such as an out-of-range number or an undeclared key inside a nested object. What the host does with such a value decides the impact.\n\nThis issue affects beam_mcp: from 0.1.0 before 0.10.1.","state":0,"publishedAt":"2026-10-08T13:40:55.828+00:00","modifiedAt":"2026-10-08T14:09:41.54+00:00","affected":[{"ecosystem":"https://repo.hex.pm","name":"beam_mcp","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"collectionURL\": \"https://repo.hex.pm\",\n                    \"cpes\": [\n                        \"cpe:2.3:a:scriptkittyos:beam_mcp:*:*:*:*:*:*:*:*\"\n                    ],\n                    \"defaultStatus\": \"unaffected\",\n                    \"modules\": [\n                        \"'Elixir.BeamMCP.Schema'\",\n                        \"'Elixir.BeamMCP.Server'\"\n                    ],\n                    \"packageName\": \"beam_mcp\",\n                    \"packageURL\": \"pkg:hex/beam_mcp\",\n                    \"product\": \"beam_mcp\",\n                    \"programFiles\": [\n                        \"lib/beam_mcp/schema.ex\",\n                        \"lib/beam_mcp/server.ex\"\n                    ],\n                    \"programRoutines\": [\n                        {\n                            \"name\": \"'Elixir.BeamMCP.Schema':validate/2\"\n                        },\n                        {\n                            \"name\": \"'Elixir.BeamMCP.Server':handle_message/2\"\n                        }\n                    ],\n                    \"repo\": \"https://github.com/ScriptKittyOS/beam_mcp\",\n                    \"vendor\": \"ScriptKittyOS\",\n                    \"versions\": [\n                        {\n                            \"lessThan\": \"0.10.1\",\n                            \"status\": \"affected\",\n                            \"version\": \"0.1.0\",\n                            \"versionType\": \"semver\"\n                        }\n                    ]\n                }"},{"ecosystem":"https://github.com","name":"scriptkittyos/beam_mcp","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"collectionURL\": \"https://github.com\",\n                    \"cpes\": [\n                        \"cpe:2.3:a:scriptkittyos:beam_mcp:*:*:*:*:*:*:*:*\"\n                    ],\n                    \"defaultStatus\": \"unaffected\",\n                    \"modules\": [\n                        \"'Elixir.BeamMCP.Schema'\",\n                        \"'Elixir.BeamMCP.Server'\"\n                    ],\n                    \"packageName\": \"scriptkittyos/beam_mcp\",\n                    \"packageURL\": \"pkg:github/scriptkittyos/beam_mcp\",\n                    \"product\": \"beam_mcp\",\n                    \"programFiles\": [\n                        \"lib/beam_mcp/schema.ex\",\n                        \"lib/beam_mcp/server.ex\"\n                    ],\n                    \"programRoutines\": [\n                        {\n                            \"name\": \"'Elixir.BeamMCP.Schema':validate/2\"\n                        },\n                        {\n                            \"name\": \"'Elixir.BeamMCP.Server':handle_message/2\"\n                        }\n                    ],\n                    \"repo\": \"https://github.com/ScriptKittyOS/beam_mcp\",\n                    \"vendor\": \"ScriptKittyOS\",\n                    \"versions\": [\n                        {\n                            \"lessThan\": \"289dbdbad641943b29a3b8d1eb36506cc8cec10a\",\n                            \"status\": \"affected\",\n                            \"version\": \"083838eb8e17fe5f6fcaf761bdbe203110288b0b\",\n                            \"versionType\": \"git\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N","score":5.3,"severity":"MEDIUM"}],"references":["https://github.com/ScriptKittyOS/beam_mcp/security/advisories/GHSA-mrg2-4747-fmpw","https://cna.erlef.org/cves/CVE-2026-88257.html","https://osv.dev/vulnerability/EEF-CVE-2026-88257","https://github.com/ScriptKittyOS/beam_mcp/commit/083838eb8e17fe5f6fcaf761bdbe203110288b0b","https://github.com/ScriptKittyOS/beam_mcp/commit/289dbdbad641943b29a3b8d1eb36506cc8cec10a"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-88257","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-88257","identifiers":["CVE-2026-88257"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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