mcp-hardened
A deliberately small MCP server that demonstrates security hardening against the OWASP MCP Top 10 with tools for file search, record queries, and document fetching, each defended against path traversal, SQL injection, and SSRF.
README
MCP-HARDENED
A deliberately small MCP server built to demonstrate security hardening against the OWASP MCP Top 10, with a test suite that proves the defenses hold.
Status
In progress. Stage 3 of 7 — 3 working tools that are vulnerable to exploitation on purpose.
Warning
Early commits contain intentionally vulnerable implementations. The build order is deliberate: write the naive version, write attack tests that prove the vulnerability is reachable, then harden until the tests pass. A security test that has never failed is not a test.
Do not use any commit from this repo as a reference implementation until the hardening commits land.
Planned scope
Three read-only tools, each hosting one vulnerability class:
| Tool | Vulnerability class | Defense |
|---|---|---|
search_files |
Path traversal | Resolve path, assert inside sandbox root |
query_records |
SQL injection | Parameterized queries only |
fetch_doc |
SSRF | Domain allowlist, revalidated after redirects |
Plus audit logging of every tool call and its arguments.
Explicitly out of scope
- Prompt injection — unsolved industry-wide, not attempting
- Tool poisoning — a consuming-side threat; a server cannot prevent a client from connecting to a poisoned server
- Multi-user authentication, rate limiting
Stack
Python 3.12 · FastMCP 3.3.1 · pytest · stdio transport
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