CVE-2026-88257

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. 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. This issue affects beam_mcp: from 0.1.0 before 0.10.1.

CVSS

No CVSS.

References

Link	Resource
https://cna.erlef.org/cves/CVE-2026-88257.html
https://github.com/ScriptKittyOS/beam_mcp/commit/083838eb8e17fe5f6fcaf761bdbe203110288b0b
https://github.com/ScriptKittyOS/beam_mcp/commit/289dbdbad641943b29a3b8d1eb36506cc8cec10a
https://github.com/ScriptKittyOS/beam_mcp/security/advisories/GHSA-mrg2-4747-fmpw
https://osv.dev/vulnerability/EEF-CVE-2026-88257

Configurations

No configuration.

History

08 Oct 2026, 14:17

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-10-08 14:17

Updated : 2026-10-08 21:01

NVD link : CVE-2026-88257

Mitre link : CVE-2026-88257

CVE.ORG link : CVE-2026-88257

JSON object : View

Products Affected

No product.

CWE

CWE-20

Improper Input Validation

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