CVE-2026-104634 | BDVDB-2026-384669 Detail
ScriptKittyOSbeam_mcp
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.
Impact#
A host that branches on a boolean argument takes the opposite branch for false, so a safety guard such as confirm: false or dry_run: false is read as set. The client already controls the argument, so the gain over sending true is limited to hosts and intermediaries that treat the two values differently.
Weaknesses#
- CWE-704 Incorrect Type Conversion or Cast
References#
- https://github.com/ScriptKittyOS/beam_mcp/security/advisories/GHSA-wv7p-j6qh-3hj4
- https://cna.erlef.org/cves/CVE-2026-104634.html
- https://osv.dev/vulnerability/EEF-CVE-2026-104634
- https://github.com/ScriptKittyOS/beam_mcp/commit/083838eb8e17fe5f6fcaf761bdbe203110288b0b
- https://github.com/ScriptKittyOS/beam_mcp/commit/289dbdbad641943b29a3b8d1eb36506cc8cec10a
Exploit#
No public exploit known
History#
- Version 1Record published in the CVE List.