---
id: CVE-2026-104634
title: >-
  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"
summary: >-
  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". A…
severity: low
cvss: 2.3
cvssVector: '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'
cwe:
  - CWE-704
vendor: ScriptKittyOS
product: beam_mcp
affected:
  - beam_mcp >= 0.1.0 < 0.10.1
  - >-
    scriptkittyos/beam_mcp >= 083838eb8e17fe5f6fcaf761bdbe203110288b0b <
    289dbdbad641943b29a3b8d1eb36506cc8cec10a
published: '2026-10-08'
updated: '2026-10-08'
sourceUpdated: '2026-10-08T21:01:07.830'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-104634'
references:
  - url: 'https://cna.erlef.org/cves/CVE-2026-104634.html'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/ScriptKittyOS/beam_mcp/commit/083838eb8e17fe5f6fcaf761bdbe203110288b0b
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/ScriptKittyOS/beam_mcp/commit/289dbdbad641943b29a3b8d1eb36506cc8cec10a
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/ScriptKittyOS/beam_mcp/security/advisories/GHSA-wv7p-j6qh-3hj4
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://osv.dev/vulnerability/EEF-CVE-2026-104634'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-10-08T13:58:26.222349Z'
cvssSource: cna
ingestedAt: '2026-10-08T14:47:16.340Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.