CVE-2026-88257
beam_mcp: nested tool argument constraints advertised but not enforced
- State
- Published
- Severity
- 5.3 Medium
- Published
- Oct 8, 2026
- Updated
- Oct 8, 2026
- Reserved
- Oct 7, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 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 | EEF |
Weaknesses
- CWE-20 Improper Input Validation
Affected Products
| Product | Versions |
|---|---|
beam_mcpScriptKittyOS |
|
beam_mcpScriptKittyOS |
|
References
- GitHub Advisoryrelatedvendor-advisory
- EEF CNA record for CVE-2026-88257related
- OSV record EEF-CVE-2026-88257related
- Introducing commit 083838e in ScriptKittyOS/beam_mcprelated
- Fix commit 289dbdb in ScriptKittyOS/beam_mcppatch
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