CVE-2026-88257

{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-88257", "assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "state": "PUBLISHED", "assignerShortName": "EEF", "dateReserved": "2026-10-07T22:15:01.878Z", "datePublished": "2026-10-08T13:40:55.828Z", "dateUpdated": "2026-10-08T14:09:41.540Z"}, "containers": {"cna": {"affected": [{"collectionURL": "https://repo.hex.pm", "cpes": ["cpe:2.3:a:scriptkittyos:beam_mcp:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["'Elixir.BeamMCP.Schema'", "'Elixir.BeamMCP.Server'"], "packageName": "beam_mcp", "packageURL": "pkg:hex/beam_mcp", "product": "beam_mcp", "programFiles": ["lib/beam_mcp/schema.ex", "lib/beam_mcp/server.ex"], "programRoutines": [{"name": "'Elixir.BeamMCP.Schema':validate/2"}, {"name": "'Elixir.BeamMCP.Server':handle_message/2"}], "repo": "https://github.com/ScriptKittyOS/beam_mcp", "vendor": "ScriptKittyOS", "versions": [{"lessThan": "0.10.1", "status": "affected", "version": "0.1.0", "versionType": "semver"}]}, {"collectionURL": "https://github.com", "cpes": ["cpe:2.3:a:scriptkittyos:beam_mcp:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["'Elixir.BeamMCP.Schema'", "'Elixir.BeamMCP.Server'"], "packageName": "scriptkittyos/beam_mcp", "packageURL": "pkg:github/scriptkittyos/beam_mcp", "product": "beam_mcp", "programFiles": ["lib/beam_mcp/schema.ex", "lib/beam_mcp/server.ex"], "programRoutines": [{"name": "'Elixir.BeamMCP.Schema':validate/2"}, {"name": "'Elixir.BeamMCP.Server':handle_message/2"}], "repo": "https://github.com/ScriptKittyOS/beam_mcp", "vendor": "ScriptKittyOS", "versions": [{"lessThan": "289dbdbad641943b29a3b8d1eb36506cc8cec10a", "status": "affected", "version": "083838eb8e17fe5f6fcaf761bdbe203110288b0b", "versionType": "git"}]}], "cpeApplicability": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:a:scriptkittyos:beam_mcp:*:*:*:*:*:*:*:*", "versionEndExcluding": "0.10.1", "versionStartIncluding": "0.1.0", "vulnerable": true}], "negate": false, "operator": "OR"}], "operator": "AND"}], "credits": [{"lang": "en", "type": "finder", "value": "Ayla Croft / Script Kitty OS"}, {"lang": "en", "type": "reporter", "value": "Ayla Croft / Script Kitty OS"}, {"lang": "en", "type": "remediation developer", "value": "Ayla Croft / Script Kitty OS"}, {"lang": "en", "type": "coordinator", "value": "Jonatan M\u00e4nnchen / EEF"}], "dateAssigned": "2026-10-08T13:40:44.000Z", "datePublic": "2026-09-26T00:00:00.000Z", "descriptions": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<p>Improper Input Validation vulnerability in <code>BeamMCP.Schema</code> 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. <code>BeamMCP.Schema.validate/2</code> checked <code>type</code>, <code>required</code>, <code>additionalProperties</code>, <code>enum</code> and numeric bounds on the top-level arguments object only. Constraints inside nested objects and on array items (<code>items</code>, <code>minItems</code>, <code>maxItems</code>, <code>minLength</code>, <code>maxLength</code>, <code>pattern</code>, nested <code>required</code>, <code>enum</code> and <code>additionalProperties: false</code>) were advertised by <code>tools/list</code> and never checked at <code>tools/call</code> or <code>prompts/get</code>, and keywords outside the enforced subset (<code>oneOf</code>, <code>anyOf</code>, <code>$ref</code>) were advertised and ignored.</p>\n<p>A host whose dispatch code relies on the schema it declared receives values the schema forbids, such as an out-of-range number or an undeclared key inside a nested object. What the host does with such a value decides the impact.</p>\n<p>This issue affects beam_mcp: from 0.1.0 before 0.10.1.</p>"}, {"base64": false, "type": "text/markdown", "value": "Improper Input Validation vulnerability in `BeamMCP.Schema` in ScriptKittyOS beam_mcp allows an MCP client to reach a tool's dispatch function with arguments that violate the input schema the server advertised. `BeamMCP.Schema.validate/2` checked `type`, `required`, `additionalProperties`, `enum` and numeric bounds on the top-level arguments object only. Constraints inside nested objects and on array items (`items`, `minItems`, `maxItems`, `minLength`, `maxLength`, `pattern`, nested `required`, `enum` and `additionalProperties: false`) were advertised by `tools/list` and never checked at `tools/call` or `prompts/get`, and keywords outside the enforced subset (`oneOf`, `anyOf`, `$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."}], "value": "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."}], "impacts": [{"capecId": "CAPEC-153", "descriptions": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<p>An MCP client can hand a host's tool values the host's declared schema forbids, such as an out-of-range number or an undeclared key inside a nested object. The consequence depends on what the host's dispatch code does with a value it never expected to receive.</p>"}, {"base64": false, "type": "text/markdown", "value": "An MCP client can hand a host's tool values the host's declared schema forbids, such as an out-of-range number or an undeclared key inside a nested object. The consequence depends on what the host's dispatch code does with a value it never expected to receive."}], "value": "An MCP client can hand a host's tool values the host's declared schema forbids, such as an out-of-range number or an undeclared key inside a nested object. The consequence depends on what the host's dispatch code does with a value it never expected to receive."}]}], "metrics": [{"cvssV4_0": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "NONE", "attackVector": "NETWORK", "baseScore": 5.3, "baseSeverity": "MEDIUM", "privilegesRequired": "LOW", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "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", "version": "4.0", "vulnAvailabilityImpact": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "LOW", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}]}], "problemTypes": [{"descriptions": [{"cweId": "CWE-20", "description": "CWE-20 Improper Input Validation", "lang": "en", "type": "CWE"}]}], "providerMetadata": {"orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "shortName": "EEF", "dateUpdated": "2026-10-08T14:09:41.540Z"}, "references": [{"name": "GitHub Advisory", "tags": ["related", "vendor-advisory"], "url": "https://github.com/ScriptKittyOS/beam_mcp/security/advisories/GHSA-mrg2-4747-fmpw"}, {"name": "EEF CNA record for CVE-2026-88257", "tags": ["related"], "url": "https://cna.erlef.org/cves/CVE-2026-88257.html"}, {"name": "OSV record EEF-CVE-2026-88257", "tags": ["related"], "url": "https://osv.dev/vulnerability/EEF-CVE-2026-88257"}, {"name": "Introducing commit 083838e in ScriptKittyOS/beam_mcp", "tags": ["related"], "url": "https://github.com/ScriptKittyOS/beam_mcp/commit/083838eb8e17fe5f6fcaf761bdbe203110288b0b"}, {"name": "Fix commit 289dbdb in ScriptKittyOS/beam_mcp", "tags": ["patch"], "url": "https://github.com/ScriptKittyOS/beam_mcp/commit/289dbdbad641943b29a3b8d1eb36506cc8cec10a"}], "source": {"discovery": "INTERNAL"}, "title": "beam_mcp: nested tool argument constraints advertised but not enforced", "workarounds": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<p>Re-validate the arguments inside the host's dispatch function against every constraint the schema declares below the top level, or move each constraint to a top-level property, which the affected versions do enforce.</p>"}, {"base64": false, "type": "text/markdown", "value": "Re-validate the arguments inside the host's dispatch function against every constraint the schema declares below the top level, or move each constraint to a top-level property, which the affected versions do enforce."}], "value": "Re-validate the arguments inside the host's dispatch function against every constraint the schema declares below the top level, or move each constraint to a top-level property, which the affected versions do enforce."}], "x_proofOfConcept": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<ol>\n<li>Declare a tool whose <code>input_schema</code> has a nested object property <code>opts</code> with <code>\"properties\": {\"level\": {\"type\": \"integer\", \"maximum\": 3}}</code>, <code>\"required\": [\"level\"]</code> and <code>\"additionalProperties\": false</code>, and an array property <code>tags</code> with <code>\"items\": {\"type\": \"string\"}</code> and <code>\"maxItems\": 2</code>.</li>\n<li>Send <code>tools/call</code> with <code>\"arguments\": {\"opts\": {\"level\": 99, \"extra\": \"x\"}}</code>.</li>\n<li>On beam_mcp 0.10.0 the dispatch function receives <code>%{opts: %{\"extra\" =&gt; \"x\", \"level\" =&gt; 99}}</code>. On 0.10.1 the call is refused with <code>invalid arguments: unknown property: opts.extra</code>.</li>\n<li>Send <code>\"arguments\": {\"tags\": [1, 2, 3]}</code>. On 0.10.0 the dispatch function receives <code>tags: [1, 2, 3]</code>. On 0.10.1 the call is refused with <code>tags must have at most 2 items</code>.</li>\n</ol>"}, {"base64": false, "type": "text/markdown", "value": "1. Declare a tool whose `input_schema` has a nested object property `opts` with `\"properties\": {\"level\": {\"type\": \"integer\", \"maximum\": 3}}`, `\"required\": [\"level\"]` and `\"additionalProperties\": false`, and an array property `tags` with `\"items\": {\"type\": \"string\"}` and `\"maxItems\": 2`.\n2. Send `tools/call` with `\"arguments\": {\"opts\": {\"level\": 99, \"extra\": \"x\"}}`.\n3. On beam_mcp 0.10.0 the dispatch function receives `%{opts: %{\"extra\" => \"x\", \"level\" => 99}}`. On 0.10.1 the call is refused with `invalid arguments: unknown property: opts.extra`.\n4. Send `\"arguments\": {\"tags\": [1, 2, 3]}`. On 0.10.0 the dispatch function receives `tags: [1, 2, 3]`. On 0.10.1 the call is refused with `tags must have at most 2 items`."}], "value": "* Declare a tool whose input_schema has a nested object property opts with \"properties\": {\"level\": {\"type\": \"integer\", \"maximum\": 3}}, \"required\": [\"level\"] and \"additionalProperties\": false, and an array property tags with \"items\": {\"type\": \"string\"} and \"maxItems\": 2.\n* Send tools/call with \"arguments\": {\"opts\": {\"level\": 99, \"extra\": \"x\"}}.\n* On beam_mcp 0.10.0 the dispatch function receives %{opts: %{\"extra\" => \"x\", \"level\" => 99}}. On 0.10.1 the call is refused with invalid arguments: unknown property: opts.extra.\n* Send \"arguments\": {\"tags\": [1, 2, 3]}. On 0.10.0 the dispatch function receives tags: [1, 2, 3]. On 0.10.1 the call is refused with tags must have at most 2 items."}], "x_technicalAnalysis": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<p><strong>1. Advertising.</strong> <code>tools/list</code> returns each tool's <code>input_schema</code> verbatim, including nested <code>properties</code>, <code>items</code> and constraint keywords.</p>\n<p><strong>2. Validation.</strong> <code>BeamMCP.Schema.validate/2</code> in <code>lib/beam_mcp/schema.ex</code> walks only the first level: <code>check_required/2</code> and <code>check_additional/3</code> run on the top-level object, and <code>check_properties/2</code> applies <code>check_type</code>, <code>check_enum</code> and <code>check_range</code> to each top-level value. A value of type <code>object</code> or <code>array</code> is accepted once its own type matches, and its contents are not visited. Keywords the validator does not know are ignored.</p>\n<p><strong>3. Dispatch.</strong> <code>BeamMCP.Server.validate_and_dispatch/3</code> passes the accepted arguments to <code>normalize_arguments/2</code> and then to the host's dispatch function, so an undeclared key inside a nested object, an out-of-range nested number, or an array item of the wrong type reaches host code that believed the schema excluded it. The same validator runs on <code>prompts/get</code> arguments. The fix in 0.10.1 enforces every keyword of the documented subset at every depth and refuses a schema that uses any other keyword when the catalog is loaded.</p>"}, {"base64": false, "type": "text/markdown", "value": "**1. Advertising.** `tools/list` returns each tool's `input_schema` verbatim, including nested `properties`, `items` and constraint keywords.\n\n**2. Validation.** `BeamMCP.Schema.validate/2` in `lib/beam_mcp/schema.ex` walks only the first level: `check_required/2` and `check_additional/3` run on the top-level object, and `check_properties/2` applies `check_type`, `check_enum` and `check_range` to each top-level value. A value of type `object` or `array` is accepted once its own type matches, and its contents are not visited. Keywords the validator does not know are ignored.\n\n**3. Dispatch.** `BeamMCP.Server.validate_and_dispatch/3` passes the accepted arguments to `normalize_arguments/2` and then to the host's dispatch function, so an undeclared key inside a nested object, an out-of-range nested number, or an array item of the wrong type reaches host code that believed the schema excluded it. The same validator runs on `prompts/get` arguments. The fix in 0.10.1 enforces every keyword of the documented subset at every depth and refuses a schema that uses any other keyword when the catalog is loaded."}], "value": "1. Advertising. tools/list returns each tool's input_schema verbatim, including nested properties, items and constraint keywords.\n\n2. Validation. BeamMCP.Schema.validate/2 in lib/beam_mcp/schema.ex walks only the first level: check_required/2 and check_additional/3 run on the top-level object, and check_properties/2 applies check_type, check_enum and check_range to each top-level value. A value of type object or array is accepted once its own type matches, and its contents are not visited. Keywords the validator does not know are ignored.\n\n3. Dispatch. BeamMCP.Server.validate_and_dispatch/3 passes the accepted arguments to normalize_arguments/2 and then to the host's dispatch function, so an undeclared key inside a nested object, an out-of-range nested number, or an array item of the wrong type reaches host code that believed the schema excluded it. The same validator runs on prompts/get arguments. The fix in 0.10.1 enforces every keyword of the documented subset at every depth and refuses a schema that uses any other keyword when the catalog is loaded."}]}, "adp": [{"metrics": [{"other": {"type": "ssvc", "content": {"timestamp": "2026-10-08T13:59:14.866448Z", "id": "CVE-2026-88257", "options": [{"Exploitation": "none"}, {"Automatable": "no"}, {"Technical Impact": "partial"}], "role": "CISA Coordinator", "version": "2.0.3"}}}], "title": "CISA ADP Vulnrichment", "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-10-08T13:59:33.374Z"}}]}}

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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, $ref) were advertised and ignored.\n\nA host whose dispatch code relies on the schema it declared receives values the schema forbids, such as an out-of-range number or an undeclared key inside a nested object. What the host does with such a value decides the impact.\n\nThis issue affects beam_mcp: from 0.1.0 before 0.10.1.", "supportingMedia": [{"type": "text/html", "value": "<p>Improper Input Validation vulnerability in <code>BeamMCP.Schema</code> in ScriptKittyOS beam_mcp allows an MCP client to reach a tool's dispatch function with arguments that violate the input schema the server advertised. <code>BeamMCP.Schema.validate/2</code> checked <code>type</code>, <code>required</code>, <code>additionalProperties</code>, <code>enum</code> and numeric bounds on the top-level arguments object only. Constraints inside nested objects and on array items (<code>items</code>, <code>minItems</code>, <code>maxItems</code>, <code>minLength</code>, <code>maxLength</code>, <code>pattern</code>, nested <code>required</code>, <code>enum</code> and <code>additionalProperties: false</code>) were advertised by <code>tools/list</code> and never checked at <code>tools/call</code> or <code>prompts/get</code>, and keywords outside the enforced subset (<code>oneOf</code>, <code>anyOf</code>, <code>$ref</code>) were advertised and ignored.</p>\n<p>A 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.</p>\n<p>This issue affects beam_mcp: from 0.1.0 before 0.10.1.</p>", "base64": false}, {"type": "text/markdown", "value": "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.", "base64": false}]}], "problemTypes": [{"descriptions": [{"lang": "en", "type": "CWE", "cweId": "CWE-20", "description": "CWE-20 Improper Input Validation"}]}], "cpeApplicability": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:scriptkittyos:beam_mcp:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "0.10.1", "versionStartIncluding": "0.1.0"}], "operator": "OR"}], "operator": "AND"}], "providerMetadata": {"orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "shortName": "EEF", "dateUpdated": "2026-10-08T14:09:41.540Z"}, "x_proofOfConcept": [{"lang": "en", "value": "* Declare a tool whose input_schema has a nested object property opts with \"properties\": {\"level\": {\"type\": \"integer\", \"maximum\": 3}}, \"required\": [\"level\"] and \"additionalProperties\": false, and an array property tags with \"items\": {\"type\": \"string\"} and \"maxItems\": 2.\n* Send tools/call with \"arguments\": {\"opts\": {\"level\": 99, \"extra\": \"x\"}}.\n* On beam_mcp 0.10.0 the dispatch function receives %{opts: %{\"extra\" => \"x\", \"level\" => 99}}. On 0.10.1 the call is refused with invalid arguments: unknown property: opts.extra.\n* Send \"arguments\": {\"tags\": [1, 2, 3]}. On 0.10.0 the dispatch function receives tags: [1, 2, 3]. On 0.10.1 the call is refused with tags must have at most 2 items.", "supportingMedia": [{"type": "text/html", "value": "<ol>\n<li>Declare a tool whose <code>input_schema</code> has a nested object property <code>opts</code> with <code>\"properties\": {\"level\": {\"type\": \"integer\", \"maximum\": 3}}</code>, <code>\"required\": [\"level\"]</code> and <code>\"additionalProperties\": false</code>, and an array property <code>tags</code> with <code>\"items\": {\"type\": \"string\"}</code> and <code>\"maxItems\": 2</code>.</li>\n<li>Send <code>tools/call</code> with <code>\"arguments\": {\"opts\": {\"level\": 99, \"extra\": \"x\"}}</code>.</li>\n<li>On beam_mcp 0.10.0 the dispatch function receives <code>%{opts: %{\"extra\" =&gt; \"x\", \"level\" =&gt; 99}}</code>. On 0.10.1 the call is refused with <code>invalid arguments: unknown property: opts.extra</code>.</li>\n<li>Send <code>\"arguments\": {\"tags\": [1, 2, 3]}</code>. On 0.10.0 the dispatch function receives <code>tags: [1, 2, 3]</code>. On 0.10.1 the call is refused with <code>tags must have at most 2 items</code>.</li>\n</ol>", "base64": false}, {"type": "text/markdown", "value": "1. Declare a tool whose `input_schema` has a nested object property `opts` with `\"properties\": {\"level\": {\"type\": \"integer\", \"maximum\": 3}}`, `\"required\": [\"level\"]` and `\"additionalProperties\": false`, and an array property `tags` with `\"items\": {\"type\": \"string\"}` and `\"maxItems\": 2`.\n2. Send `tools/call` with `\"arguments\": {\"opts\": {\"level\": 99, \"extra\": \"x\"}}`.\n3. On beam_mcp 0.10.0 the dispatch function receives `%{opts: %{\"extra\" => \"x\", \"level\" => 99}}`. On 0.10.1 the call is refused with `invalid arguments: unknown property: opts.extra`.\n4. Send `\"arguments\": {\"tags\": [1, 2, 3]}`. On 0.10.0 the dispatch function receives `tags: [1, 2, 3]`. On 0.10.1 the call is refused with `tags must have at most 2 items`.", "base64": false}]}], "x_technicalAnalysis": [{"lang": "en", "value": "1. Advertising. tools/list returns each tool's input_schema verbatim, including nested properties, items and constraint keywords.\n\n2. Validation. BeamMCP.Schema.validate/2 in lib/beam_mcp/schema.ex walks only the first level: check_required/2 and check_additional/3 run on the top-level object, and check_properties/2 applies check_type, check_enum and check_range to each top-level value. A value of type object or array is accepted once its own type matches, and its contents are not visited. Keywords the validator does not know are ignored.\n\n3. Dispatch. BeamMCP.Server.validate_and_dispatch/3 passes the accepted arguments to normalize_arguments/2 and then to the host's dispatch function, so an undeclared key inside a nested object, an out-of-range nested number, or an array item of the wrong type reaches host code that believed the schema excluded it. The same validator runs on prompts/get arguments. The fix in 0.10.1 enforces every keyword of the documented subset at every depth and refuses a schema that uses any other keyword when the catalog is loaded.", "supportingMedia": [{"type": "text/html", "value": "<p><strong>1. Advertising.</strong> <code>tools/list</code> returns each tool's <code>input_schema</code> verbatim, including nested <code>properties</code>, <code>items</code> and constraint keywords.</p>\n<p><strong>2. Validation.</strong> <code>BeamMCP.Schema.validate/2</code> in <code>lib/beam_mcp/schema.ex</code> walks only the first level: <code>check_required/2</code> and <code>check_additional/3</code> run on the top-level object, and <code>check_properties/2</code> applies <code>check_type</code>, <code>check_enum</code> and <code>check_range</code> to each top-level value. A value of type <code>object</code> or <code>array</code> is accepted once its own type matches, and its contents are not visited. Keywords the validator does not know are ignored.</p>\n<p><strong>3. Dispatch.</strong> <code>BeamMCP.Server.validate_and_dispatch/3</code> passes the accepted arguments to <code>normalize_arguments/2</code> and then to the host's dispatch function, so an undeclared key inside a nested object, an out-of-range nested number, or an array item of the wrong type reaches host code that believed the schema excluded it. The same validator runs on <code>prompts/get</code> arguments. The fix in 0.10.1 enforces every keyword of the documented subset at every depth and refuses a schema that uses any other keyword when the catalog is loaded.</p>", "base64": false}, {"type": "text/markdown", "value": "**1. Advertising.** `tools/list` returns each tool's `input_schema` verbatim, including nested `properties`, `items` and constraint keywords.\n\n**2. Validation.** `BeamMCP.Schema.validate/2` in `lib/beam_mcp/schema.ex` walks only the first level: `check_required/2` and `check_additional/3` run on the top-level object, and `check_properties/2` applies `check_type`, `check_enum` and `check_range` to each top-level value. A value of type `object` or `array` is accepted once its own type matches, and its contents are not visited. Keywords the validator does not know are ignored.\n\n**3. Dispatch.** `BeamMCP.Server.validate_and_dispatch/3` passes the accepted arguments to `normalize_arguments/2` and then to the host's dispatch function, so an undeclared key inside a nested object, an out-of-range nested number, or an array item of the wrong type reaches host code that believed the schema excluded it. The same validator runs on `prompts/get` arguments. The fix in 0.10.1 enforces every keyword of the documented subset at every depth and refuses a schema that uses any other keyword when the catalog is loaded.", "base64": false}]}]}}, "cveMetadata": {"cveId": "CVE-2026-88257", "state": "PUBLISHED", "dateUpdated": "2026-10-08T14:09:41.540Z", "dateReserved": "2026-10-07T22:15:01.878Z", "assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "datePublished": "2026-10-08T13:40:55.828Z", "assignerShortName": "EEF"}, "dataVersion": "5.2"}

{"affected": [{"affectedData": [{"collectionURL": "https://repo.hex.pm", "cpes": ["cpe:2.3:a:scriptkittyos:beam_mcp:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["'Elixir.BeamMCP.Schema'", "'Elixir.BeamMCP.Server'"], "packageName": "beam_mcp", "packageURL": "pkg:hex/beam_mcp", "product": "beam_mcp", "programFiles": ["lib/beam_mcp/schema.ex", "lib/beam_mcp/server.ex"], "programRoutines": [{"name": "'Elixir.BeamMCP.Schema':validate/2"}, {"name": "'Elixir.BeamMCP.Server':handle_message/2"}], "repo": "https://github.com/ScriptKittyOS/beam_mcp", "vendor": "ScriptKittyOS", "versions": [{"lessThan": "0.10.1", "status": "affected", "version": "0.1.0", "versionType": "semver"}]}, {"collectionURL": "https://github.com", "cpes": ["cpe:2.3:a:scriptkittyos:beam_mcp:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["'Elixir.BeamMCP.Schema'", "'Elixir.BeamMCP.Server'"], "packageName": "scriptkittyos/beam_mcp", "packageURL": "pkg:github/scriptkittyos/beam_mcp", "product": "beam_mcp", "programFiles": ["lib/beam_mcp/schema.ex", "lib/beam_mcp/server.ex"], "programRoutines": [{"name": "'Elixir.BeamMCP.Schema':validate/2"}, {"name": "'Elixir.BeamMCP.Server':handle_message/2"}], "repo": "https://github.com/ScriptKittyOS/beam_mcp", "vendor": "ScriptKittyOS", "versions": [{"lessThan": "289dbdbad641943b29a3b8d1eb36506cc8cec10a", "status": "affected", "version": "083838eb8e17fe5f6fcaf761bdbe203110288b0b", "versionType": "git"}]}], "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"}], "cveTags": [], "descriptions": [{"lang": "en", "value": "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."}], "id": "CVE-2026-88257", "lastModified": "2026-10-08T21:01:07.830", "metrics": {"cvssMetricV40": [{"cvssData": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "NONE", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 5.3, "baseSeverity": "MEDIUM", "confidentialityRequirement": "NOT_DEFINED", "exploitMaturity": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "privilegesRequired": "LOW", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "version": "4.0", "vulnAvailabilityImpact": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "LOW", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-88257", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-10-08T13:59:14.866448Z", "version": "2.0.3"}}]}, "published": "2026-10-08T14:17:01.613", "references": [{"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://cna.erlef.org/cves/CVE-2026-88257.html"}, {"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://github.com/ScriptKittyOS/beam_mcp/commit/083838eb8e17fe5f6fcaf761bdbe203110288b0b"}, {"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://github.com/ScriptKittyOS/beam_mcp/commit/289dbdbad641943b29a3b8d1eb36506cc8cec10a"}, {"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://github.com/ScriptKittyOS/beam_mcp/security/advisories/GHSA-mrg2-4747-fmpw"}, {"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://osv.dev/vulnerability/EEF-CVE-2026-88257"}], "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "vulnStatus": "Deferred", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-20"}], "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "type": "Secondary"}]}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[0.1.0,0.10.1)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[083838eb8e17fe5f6fcaf761bdbe203110288b0b,289dbdbad641943b29a3b8d1eb36506cc8cec10a)"}}], "enrichment": {"confidence": 100.0, "confidence_source": "cna", "scores": [{"score": 100.0, "source": "cna"}]}, "original": {"product": "beam_mcp", "source": "cna", "vendor": "ScriptKittyOS"}, "product": "beam_mcp", "vendor": "scriptkittyos"}, {"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[083838eb8e17fe5f6fcaf761bdbe203110288b0b,289dbdbad641943b29a3b8d1eb36506cc8cec10a)"}}], "enrichment": {"confidence": 100.0, "confidence_source": "cna", "scores": [{"score": 100.0, "source": "cna"}]}, "original": {"product": "beam_mcp", "source": "cna", "vendor": "ScriptKittyOS"}, "product": "beam_mcp", "vendor": "scriptkittyos"}], "created": "2026-10-08T16:30:05.143007+00:00", "updated": "2026-10-09T08:04:57.339290+00:00", "vendors": ["scriptkittyos", "scriptkittyos$PRODUCT$beam_mcp"]}