beam_mcp: JSON boolean and null tool arguments reach dispatch as strings
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.
CVE-2026-104634
Primary source · Revision 1
Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.
Security context
Source reference: cve:CVE-2026-104634
beam_mcp
Source reference: /containers/cna/affected/0/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
beam_mcp
Source reference: /containers/cna/affected/1/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
Structured affected-version data
Original package identities and version rules from this source.
[
{
"cpes": [
"cpe:2.3:a:scriptkittyos:beam_mcp:*:*:*:*:*:*:*:*"
],
"repo": "https://github.com/ScriptKittyOS/beam_mcp",
"vendor": "ScriptKittyOS",
"modules": [
"'Elixir.BeamMCP.Server'"
],
"product": "beam_mcp",
"versions": [
{
"status": "affected",
"version": "0.1.0",
"lessThan": "0.10.1",
"versionType": "semver"
}
],
"packageURL": "pkg:hex/beam_mcp",
"packageName": "beam_mcp",
"programFiles": [
"lib/beam_mcp/server.ex"
],
"collectionURL": "https://repo.hex.pm",
"defaultStatus": "unaffected",
"programRoutines": [
{
"name": "'Elixir.BeamMCP.Server':handle_message/2"
},
{
"name": "'Elixir.BeamMCP.Server':normalize_arguments/2"
},
{
"name": "'Elixir.BeamMCP.Server':to_json_value/1"
}
]
},
{
"cpes": [
"cpe:2.3:a:scriptkittyos:beam_mcp:*:*:*:*:*:*:*:*"
],
"repo": "https://github.com/ScriptKittyOS/beam_mcp",
"vendor": "ScriptKittyOS",
"modules": [
"'Elixir.BeamMCP.Server'"
],
"product": "beam_mcp",
"versions": [
{
"status": "affected",
"version": "083838eb8e17fe5f6fcaf761bdbe203110288b0b",
"lessThan": "289dbdbad641943b29a3b8d1eb36506cc8cec10a",
"versionType": "git"
}
],
"packageURL": "pkg:github/scriptkittyos/beam_mcp",
"packageName": "scriptkittyos/beam_mcp",
"programFiles": [
"lib/beam_mcp/server.ex"
],
"collectionURL": "https://github.com",
"defaultStatus": "unaffected",
"programRoutines": [
{
"name": "'Elixir.BeamMCP.Server':handle_message/2"
},
{
"name": "'Elixir.BeamMCP.Server':normalize_arguments/2"
},
{
"name": "'Elixir.BeamMCP.Server':to_json_value/1"
}
]
}
]- Related CVEs
- CVE-2026-104634
Source reference:
/cveMetadata/cveId
Publisher severity
low
Source reference: /containers/cna/metrics
- Event
- #12490 · Revision 1
- Added to Heist Feed
- Publisher date