beam_mcp: nested tool argument constraints advertised but not enforced
Summary
| CVE | CVE-2026-88257 |
|---|---|
| State | PUBLISHED |
| Assigner | EEF |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-10-08 14:17:01 UTC |
| Updated | 2026-10-08 21:01:07 UTC |
| 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. |
Risk And Classification
Primary CVSS: v4.0 5.3 MEDIUM from 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
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
Problem Types: CWE-20 | CWE-20 CWE-20 Improper Input Validation
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | Secondary | 5.3 | MEDIUM | 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/C... |
| 4.0 | CNA | CVSS | 5.3 | MEDIUM | 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 |
CVSS v4.0 Breakdown
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
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | ScriptKittyOS | Beam Mcp | affected 0.1.0 0.10.1 semver | Not specified |
| CNA | ScriptKittyOS | Beam Mcp | affected 083838eb8e17fe5f6fcaf761bdbe203110288b0b 289dbdbad641943b29a3b8d1eb36506cc8cec10a git | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| cna.erlef.org/cves/CVE-2026-88257.html | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | cna.erlef.org | |
| github.com/ScriptKittyOS/beam_mcp/commit/083838eb8e17fe5f6fcaf761bdbe203... | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | github.com | |
| github.com/ScriptKittyOS/beam_mcp/commit/289dbdbad641943b29a3b8d1eb36506... | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | github.com | |
| github.com/ScriptKittyOS/beam_mcp/security/advisories/GHSA-mrg2-4747-fmpw | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | github.com | |
| osv.dev/vulnerability/EEF-CVE-2026-88257 | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | osv.dev | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: Ayla Croft / Script Kitty OS (en)
CNA: Ayla Croft / Script Kitty OS (en)
CNA: Ayla Croft / Script Kitty OS (en)
CNA: Jonatan Männchen / EEF (en)
Additional Advisory Data
Workarounds
CNA: 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.