Low · CVSS 2.3CVE-2026-104634

beam_mcp: JSON boolean and null tool arguments reach dispatch as stringsCVE-2026-104634

Answer in brief

CVE-2026-104634 records a Low severity (CVSS 2.3) vulnerability in beam_mcp: JSON boolean and null tool arguments reach dispatch as strings. The current sources do not mark it as known exploited. The current feed maps ScriptKittyOS/beam_mcp (generic), ScriptKittyOS/scriptkittyos/beam_mcp (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Oct 8, 2026Updated Oct 8, 2026Source checked Oct 8, 2026First seen by HOL Oct 8, 2026Material review Oct 8, 2026

Upstream Advisory

Key facts

Risk: Low · CVSS 2.3
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 2.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps ScriptKittyOS/beam_mcp (generic), ScriptKittyOS/scriptkittyos/beam_mcp (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
ScriptKittyOS/beam_mcpgeneric	>=0.1.0 <0.10.1	0.10.1
ScriptKittyOS/scriptkittyos/beam_mcpgeneric	>=083838eb8e17fe5f6fcaf761bdbe203110288b0b <289dbdbad641943b29a3b8d1eb36506cc8cec10a	289dbdbad641943b29a3b8d1eb36506cc8cec10a

Recommended response

Check inventory. Check lockfiles and deployed manifests for ScriptKittyOS/beam_mcp, ScriptKittyOS/scriptkittyos/beam_mcp.
Review the reported fix. Source-reported workaround: 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.

Evidence timeline and material changes

Published upstream
Oct 8, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Oct 8, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Oct 8, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.