356 lines
24 KiB
JSON
356 lines
24 KiB
JSON
{
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"dataType": "CVE_RECORD",
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"dataVersion": "5.2",
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"cveMetadata": {
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"cveId": "CVE-2026-88257",
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"assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
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"state": "PUBLISHED",
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"assignerShortName": "EEF",
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"dateReserved": "2026-10-07T22:15:01.878Z",
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"datePublished": "2026-10-08T13:40:55.828Z",
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"dateUpdated": "2026-10-08T14:09:41.540Z"
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},
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"containers": {
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"cna": {
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"affected": [
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{
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"collectionURL": "https://repo.hex.pm",
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"cpes": [
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"cpe:2.3:a:scriptkittyos:beam_mcp:*:*:*:*:*:*:*:*"
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],
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"defaultStatus": "unaffected",
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"modules": [
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"'Elixir.BeamMCP.Schema'",
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"'Elixir.BeamMCP.Server'"
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],
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"packageName": "beam_mcp",
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"packageURL": "pkg:hex/beam_mcp",
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"product": "beam_mcp",
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"programFiles": [
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"lib/beam_mcp/schema.ex",
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"lib/beam_mcp/server.ex"
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],
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"programRoutines": [
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{
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"name": "'Elixir.BeamMCP.Schema':validate/2"
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},
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{
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"name": "'Elixir.BeamMCP.Server':handle_message/2"
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}
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],
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"repo": "https://github.com/ScriptKittyOS/beam_mcp",
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"vendor": "ScriptKittyOS",
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"versions": [
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{
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"lessThan": "0.10.1",
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"status": "affected",
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"version": "0.1.0",
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"versionType": "semver"
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}
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]
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},
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{
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"collectionURL": "https://github.com",
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"cpes": [
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"cpe:2.3:a:scriptkittyos:beam_mcp:*:*:*:*:*:*:*:*"
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],
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"defaultStatus": "unaffected",
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"modules": [
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"'Elixir.BeamMCP.Schema'",
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"'Elixir.BeamMCP.Server'"
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],
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"packageName": "scriptkittyos/beam_mcp",
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"packageURL": "pkg:github/scriptkittyos/beam_mcp",
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"product": "beam_mcp",
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"programFiles": [
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"lib/beam_mcp/schema.ex",
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"lib/beam_mcp/server.ex"
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],
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"programRoutines": [
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{
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"name": "'Elixir.BeamMCP.Schema':validate/2"
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},
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{
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"name": "'Elixir.BeamMCP.Server':handle_message/2"
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}
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],
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"repo": "https://github.com/ScriptKittyOS/beam_mcp",
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"vendor": "ScriptKittyOS",
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"versions": [
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{
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"lessThan": "289dbdbad641943b29a3b8d1eb36506cc8cec10a",
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"status": "affected",
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"version": "083838eb8e17fe5f6fcaf761bdbe203110288b0b",
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"versionType": "git"
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}
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]
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}
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],
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"cpeApplicability": [
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{
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"nodes": [
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{
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"cpeMatch": [
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{
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"criteria": "cpe:2.3:a:scriptkittyos:beam_mcp:*:*:*:*:*:*:*:*",
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"versionEndExcluding": "0.10.1",
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"versionStartIncluding": "0.1.0",
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"vulnerable": true
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}
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],
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"negate": false,
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"operator": "OR"
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}
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],
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"operator": "AND"
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}
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],
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"credits": [
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{
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"lang": "en",
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"type": "finder",
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"value": "Ayla Croft / Script Kitty OS"
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},
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{
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"lang": "en",
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"type": "reporter",
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"value": "Ayla Croft / Script Kitty OS"
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},
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{
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"lang": "en",
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"type": "remediation developer",
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"value": "Ayla Croft / Script Kitty OS"
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},
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{
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"lang": "en",
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"type": "coordinator",
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"value": "Jonatan Männchen / EEF"
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}
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],
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"dateAssigned": "2026-10-08T13:40:44.000Z",
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"datePublic": "2026-09-26T00:00:00.000Z",
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"descriptions": [
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{
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"lang": "en",
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"supportingMedia": [
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"base64": false,
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"type": "text/html",
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"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>$ref</code>) were advertised and ignored.</p>\n<p>A host whose dispatch code relies on the schema it declared receives values the schema forbids, such as an out-of-range number or an undeclared key inside a nested object. What the host does with such a value decides the impact.</p>\n<p>This issue affects beam_mcp: from 0.1.0 before 0.10.1.</p>"
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},
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{
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"base64": false,
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"type": "text/markdown",
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"value": "Improper Input Validation vulnerability in `BeamMCP.Schema` in ScriptKittyOS beam_mcp allows an MCP client to reach a tool's dispatch function with arguments that violate the input schema the server advertised. `BeamMCP.Schema.validate/2` checked `type`, `required`, `additionalProperties`, `enum` and numeric bounds on the top-level arguments object only. Constraints inside nested objects and on array items (`items`, `minItems`, `maxItems`, `minLength`, `maxLength`, `pattern`, nested `required`, `enum` and `additionalProperties: false`) were advertised by `tools/list` and never checked at `tools/call` or `prompts/get`, and keywords outside the enforced subset (`oneOf`, `anyOf`, `$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."
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}
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],
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"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."
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}
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],
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"impacts": [
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{
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"capecId": "CAPEC-153",
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"descriptions": [
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{
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"lang": "en",
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"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>"
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},
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"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."
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}
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"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."
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}
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]
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}
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],
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"metrics": [
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{
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"cvssV4_0": {
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"Automatable": "NOT_DEFINED",
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"Recovery": "NOT_DEFINED",
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"Safety": "NOT_DEFINED",
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"attackComplexity": "LOW",
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"attackRequirements": "NONE",
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"attackVector": "NETWORK",
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"baseScore": 5.3,
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"baseSeverity": "MEDIUM",
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"privilegesRequired": "LOW",
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"providerUrgency": "NOT_DEFINED",
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"subAvailabilityImpact": "NONE",
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"subConfidentialityImpact": "NONE",
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"subIntegrityImpact": "NONE",
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"userInteraction": "NONE",
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"valueDensity": "NOT_DEFINED",
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"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",
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"version": "4.0",
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"vulnAvailabilityImpact": "NONE",
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"vulnConfidentialityImpact": "NONE",
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"vulnIntegrityImpact": "LOW",
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"vulnerabilityResponseEffort": "NOT_DEFINED"
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},
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"format": "CVSS",
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"scenarios": [
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{
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"lang": "en",
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"value": "GENERAL"
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}
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]
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}
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],
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"problemTypes": [
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{
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"descriptions": [
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{
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"cweId": "CWE-20",
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"description": "CWE-20 Improper Input Validation",
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"lang": "en",
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"type": "CWE"
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}
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]
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}
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],
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"providerMetadata": {
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"orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
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"shortName": "EEF",
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"dateUpdated": "2026-10-08T14:09:41.540Z"
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},
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"references": [
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{
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"name": "GitHub Advisory",
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"tags": [
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"related",
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"vendor-advisory"
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],
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"url": "https://github.com/ScriptKittyOS/beam_mcp/security/advisories/GHSA-mrg2-4747-fmpw"
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},
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{
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"name": "EEF CNA record for CVE-2026-88257",
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"tags": [
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"related"
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],
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"url": "https://cna.erlef.org/cves/CVE-2026-88257.html"
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},
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{
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"name": "OSV record EEF-CVE-2026-88257",
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"tags": [
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"related"
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],
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"url": "https://osv.dev/vulnerability/EEF-CVE-2026-88257"
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},
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{
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"name": "Introducing commit 083838e in ScriptKittyOS/beam_mcp",
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"related"
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],
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"url": "https://github.com/ScriptKittyOS/beam_mcp/commit/083838eb8e17fe5f6fcaf761bdbe203110288b0b"
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},
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{
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"name": "Fix commit 289dbdb in ScriptKittyOS/beam_mcp",
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"tags": [
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"patch"
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],
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"url": "https://github.com/ScriptKittyOS/beam_mcp/commit/289dbdbad641943b29a3b8d1eb36506cc8cec10a"
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}
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],
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"source": {
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"discovery": "INTERNAL"
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},
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"title": "beam_mcp: nested tool argument constraints advertised but not enforced",
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"workarounds": [
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"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>"
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},
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{
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"type": "text/markdown",
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"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."
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}
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],
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"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."
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}
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],
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"x_proofOfConcept": [
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{
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"lang": "en",
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"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\" => \"x\", \"level\" => 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>"
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},
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"base64": false,
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"type": "text/markdown",
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"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`."
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}
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],
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"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."
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}
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],
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"x_technicalAnalysis": [
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{
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"lang": "en",
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"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>"
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},
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{
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"base64": false,
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"type": "text/markdown",
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"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."
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}
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],
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}
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]
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"adp": [
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"content": {
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"timestamp": "2026-10-08T13:59:14.866448Z",
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"id": "CVE-2026-88257",
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"options": [
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{
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"Exploitation": "none"
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