fix(mcp): validate MCP server commands and harden defaults (issue #14) - #34
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Prevents CWE-78 arbitrary command execution through MCP server config.
Commands from config.yaml are now validated against an allowlist and
checked for shell metacharacters before spawning.
Changes:
- mcp-loader.ts: Add ALLOWED_MCP_COMMANDS allowlist (npx, node, python3,
python, uvx, deno, bun) — rejects unknown binaries and absolute paths
outside allowed set
- mcp-loader.ts: Add validateMcpCommand() — rejects commands containing
shell metacharacters (|, ;, &, $, (), `, {}, \)
- mcp-loader.ts: Extend BLOCKED_ENV_KEYS with DYLD_LIBRARY_PATH,
NODE_EXTRA_CA_CERTS, PYTHONPATH, PYTHONSTARTUP, PYTHONINSPECT,
RUBYLIB, PERL5LIB, PERLLIB, SSL_CERT_FILE, SSL_CERT_DIR, PATH, HOME
- mcp-loader.ts: Change default scope from "always" to "admin-only"
- schema.ts: Export McpServerSchema for testing
- schema.ts: Change McpServerSchema scope default from "always" to "admin-only"
- New test file: mcp-loader.test.ts — 17 tests covering command validation,
allowlist enforcement, metacharacter detection, schema defaults,
blocked env keys, and config parsing
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Summary
Fixes CWE-78 (OS Command Injection) — MCP server commands from config.yaml were spawned without any validation, allowing arbitrary command execution.
Changes
src/agent/tools/mcp-loader.ts
src/config/schema.ts
src/agent/tools/tests/mcp-loader.test.ts (new)
Security Impact
Closes #14
🤖 Generated with Claude Code