Dangling Dns in Fastapi with Cockroachdb

A dangling DNS configuration in a Fastapi service that uses Cockroachdb can expose the database connection to unintended network paths. When Fastapi resolves a database hostname through DNS, it relies on the resolver behavior at runtime. If the hostname points to a stale or external address that is not restricted to the intended Cockroachdb cluster, the application may route queries to an uncontrolled endpoint. This situation commonly arises when a hostname is reused across environments or when DNS records are not synchronized with infrastructure changes.

In the context of middleBrick’s 12 security checks, this appears as an exposure in the Property Authorization and Data Exposure categories. The scanner tests unauthenticated attack surfaces and can detect whether database connection behavior allows leakage or improper routing. For Cockroachdb, which typically expects secure, internal network paths, a dangling DNS entry can break implicit network assumptions, making the endpoint reachable from unexpected network locations. This increases the risk of unauthorized access to data in transit, especially if encryption is not enforced or if the dangling record resolves to a public host.

Consider an OpenAPI spec where the database host is defined as an environment variable and resolved via DNS at startup. If the environment changes but the DNS record is not updated, Fastapi may continue to use a stale hostname. middleBrick’s OpenAPI/Swagger analysis, with full $ref resolution, cross-references spec definitions with runtime findings. It can flag that the resolved host does not match expected network boundaries, highlighting a potential data exposure path. This is particularly relevant when combined with active checks such as SSRF or unsafe consumption patterns, where an attacker might influence hostname resolution to redirect traffic.

The LLM/AI Security checks do not directly test DNS behavior, but they complement the analysis by ensuring that no system prompt or configuration details that reference unstable endpoints are leaked. For example, if error messages or logs inadvertently expose the dangling hostname, the output scanning for PII and API keys may detect sensitive connection strings. Together, these checks provide a broader view of how a misconfigured DNS setup can amplify risks across authentication, authorization, and data exposure in a Fastapi and Cockroachdb deployment.

To remediate a dangling DNS issue, ensure that the database hostname used by Fastapi is statically defined or tightly controlled through configuration management. Avoid relying on DNS records that can change independently of your deployment pipeline. Instead, use explicit network controls such as IP addresses or service discovery mechanisms that are synchronized with your infrastructure state.

Below is a syntactically correct Fastapi example using Cockroachdb with a fixed connection string and prepared statements to minimize runtime resolution risks. This approach reduces reliance on dynamic DNS and aligns with secure connection practices.

from fastapi import Fastapi, HTTPException
import psycopg2
from psycopg2 import sql

app = Fastapi()

# Use a fixed, environment-managed connection string with explicit host and port
# Avoid dynamic hostname resolution that may lead to dangling DNS
DATABASE_URL = "postgresql://myuser:[email protected]:26257/mydb?sslmode=require"

def get_db():
    conn = psycopg2.connect(DATABASE_URL)
    try:
        yield conn
    finally:
        conn.close()

@app.get("/users/{user_id}")
def read_user(user_id: int):
    conn = next(get_db())
    try:
        with conn.cursor() as cur:
            # Use parameterized queries to prevent injection
            cur.execute(sql.SQL("SELECT id, email FROM users WHERE id = %s"), [user_id])
            row = cur.fetchone()
            if row is None:
                raise HTTPException(status_code=404, detail="User not found")
            return {"id": row[0], "email": row[1]}
    finally:
        conn.close()

In this example, the host is an explicit IP address with SSL enforcement, reducing the chance of DNS misdirection. For environments that require hostnames, ensure that DNS records are managed with the same rigor as code deployments and that changes are validated before rollout. middleBrick’s CLI tool can scan this configuration and report on the effective exposure surface. Using the CLI, run middlebrick scan <url> to verify that the endpoint does not resolve to unintended hosts.

For continuous assurance, the Pro plan’s continuous monitoring can schedule regular scans of your Fastapi and Cockroachdb endpoints, alerting you if resolution behavior changes. The GitHub Action can enforce that no deployment proceeds if a scan detects a high-risk finding related to network exposure, integrating security into your CI/CD pipeline. The MCP Server allows you to initiate scans directly from your AI coding assistant, ensuring that configuration changes are reviewed in context.