beam_mcp: JSON boolean and null tool arguments reach dispatch as strings
Summary
| CVE | CVE-2026-104634 |
|---|---|
| State | PUBLISHED |
| Assigner | EEF |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-10-08 14:16:46 UTC |
| Updated | 2026-10-08 21:01:07 UTC |
| Description | Incorrect Type Conversion or Cast vulnerability in BeamMCP.Server in ScriptKittyOS beam_mcp allows an MCP client's JSON true, false and null tool arguments to reach the host's dispatch function as the strings "true", "false" and "nil". After BeamMCP.Schema.validate/2 accepted a value as a boolean, normalize_arguments/2 passed every argument through to_json_value/1, whose atom clause converts true, false and nil to strings. A string is truthy in Elixir, so a host that tests a boolean argument, for example if args.dry_run, takes the opposite branch for false, and a guard such as confirm: false reads as set. The client controls the argument and could send true directly, so the practical impact is limited to hosts whose behaviour on false differs from their behaviour on true, and to any policy layer in front of the server that permits false but refuses true. The same normalisation applies to prompts/get arguments, which exist from 0.5.0. This issue affects beam_mcp: from 0.1.0 before 0.10.1. |
Risk And Classification
Primary CVSS: v4.0 2.3 LOW from 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
CVSS:4.0/AV:N/AC:L/AT:P/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-704 | CWE-704 CWE-704 Incorrect Type Conversion or Cast
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | Secondary | 2.3 | LOW | CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/C... |
| 4.0 | CNA | CVSS | 2.3 | LOW | CVSS:4.0/AV:N/AC:L/AT:P/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:P/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 |
|---|---|---|---|
| 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 | |
| cna.erlef.org/cves/CVE-2026-104634.html | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | cna.erlef.org | |
| github.com/ScriptKittyOS/beam_mcp/security/advisories/GHSA-wv7p-j6qh-3hj4 | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | github.com | |
| osv.dev/vulnerability/EEF-CVE-2026-104634 | 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: In the host's dispatch function, compare boolean arguments against both forms, for example args.flag in [true, "true"] and args.flag in [false, "false"], and treat the string "nil" as null where the schema admits null.