CVE-2026-88257 Details
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. 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.
A vulnerability exists in the BeamMCP.Schema module of ScriptKittyOS beam_mcp, specifically in versions 0.1.0 prior to 0.10.1. This vulnerability allows an MCP client to send arguments to a tool's dispatch function that violate the input schema advertised by the server. The validation function in BeamMCP.Schema only checks top-level arguments, leaving nested object constraints and array item specifications unchecked. As a result, a host may receive unexpected values, such as out-of-range numbers or undeclared keys in nested objects, potentially leading to unintended consequences depending on how the host processes these values.
Users can upgrade to BeamMCP version 0.10.1 or later, where this vulnerability is fixed. If an immediate upgrade is not possible, re-validating arguments inside the dispatch function or adjusting the schema to avoid nested constraints can serve as a temporary workaround.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed Oct 8, 2026CISA-ADP
Assessed Oct 8, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://cna.erlef.org/cves/CVE-2026-88257.html | EEF | AdvisoryTechnical Description |
| https://github.com/ScriptKittyOS/beam_mcp/commit/083838eb8e17fe5f6fcaf761bdbe203110288b0b | EEF | Source CodeVendor |
| https://github.com/ScriptKittyOS/beam_mcp/commit/289dbdbad641943b29a3b8d1eb36506cc8cec10a | EEF | Source CodeVendor |
| https://github.com/ScriptKittyOS/beam_mcp/security/advisories/GHSA-mrg2-4747-fmpw | EEF | AdvisoryRemedyVendor |
| https://osv.dev/vulnerability/EEF-CVE-2026-88257 | EEF | AdvisoryExploit |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-20 | Improper Input Validation | EEF |
Affected Products
| Product | Versions |
|---|---|
| ScriptKittyOS beam_mcp | >= 0.1.0, < 0.10.1 (semver) |
CPE
Remediation
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Change History
2 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Oct 8, 2026 | CVE Modified | CISA-ADP |
| Oct 8, 2026 | New CVE Received | EEF |