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Tarek Mohamed
Tarek Mohamed

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MCP Postgres Guard: Preventing SQL Injections and Slow Queries in AI Agents

#ai #postgres #database #security

Giving an AI assistant access to a database through MCP can be transformative for data analytics, but executing raw LLM-generated SQL against production or staging databases carries severe risks:

  • Accidental DROP TABLE or DELETE WITHOUT WHERE clauses.
  • Expensive unindexed sequential scans locking the database.
  • SQL injection vulnerabilities.

mcp-postgres-guard is an audited, secure MCP server for PostgreSQL designed to act as a resilient safety firewall.

GitHub logo seotarek / mcp-postgres-guard

A secure Model Context Protocol (MCP) server for PostgreSQL: query auditing, slow-query analysis, and SQL injection prevention for AI agents.

MCP Postgres Guard 🐘🛡️

License: MIT Python 3.8+ MCP Protocol

A security-first Model Context Protocol (MCP) server for PostgreSQL: query auditing, destructive command interception, and SQL injection prevention for autonomous AI agents.

Developed by Tarek Mohamed (@seotarek)

📌 Why MCP Postgres Guard?

Allowing AI agents (Claude, Cursor, LangChain agents) direct SQL access creates severe operational risks: accidental table dropping, unbounded deletions, or SQL injection. MCP Postgres Guard intercepts and audits all agent-generated SQL queries before they reach your database:

[ AI Agent / Claude / Cursor ]
               │
               ▼
 ┌──────────────────────────────────────────────┐
 │           MCP Postgres Guard Server          │
 │  • Destructive Query Blocker (DROP/TRUNCATE) │
 │  • Unbounded DELETE/UPDATE Prevention        │
 │  • Stacked Query & RCE Probe Detection       │
 └──────────────────────┬───────────────────────┘
                        │ (Only If Verified Safe)
                        ▼
             [ Production Database ]

🛠️ MCP Tools

  • pg_validate_query: Validates whether a SQL statement is safe to execute for an autonomous agent.
  • pg_check_read_only: Enforces a strict read-only policy…
View on GitHub

🔒 Security Features

  1. AST Query Validation: Parses incoming SQL statements using pglast / sqlparse to enforce read-only semantics (SELECT only, no INSERT/UPDATE/DELETE/TRUNCATE/ALTER).
  2. Transaction Timeouts & Statement Limits: Caps execution time at configurable thresholds (e.g. 3000ms) to prevent Denial of Service (DoS).
  3. Query Plan Cost Analysis: Runs EXPLAIN before executing heavy queries; rejects plans with estimated costs exceeding safety budgets.
  4. Data Masking (PII): Automatically masks sensitive columns (emails, phone numbers, password hashes) in result sets.

Check out the full repository and setup guide on GitHub:
👉 https://github.com/seotarek/mcp-postgres-guard

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