Arp Spoofing in Fastapi with Cockroachdb

Arp spoofing is a Layer 2 attack where an adversary sends falsified ARP messages to associate their MAC address with the IP of a legitimate host, typically the database gateway. In a Fastapi application that uses Cockroachdb as the backend datastore, the risk is not that Fastapi or Cockroachdb introduce a protocol weakness, but that the runtime environment can be abused if network segmentation is weak. When Fastapi runs in a container or shared host environment without proper isolation, an attacker on the same local network can spoof the gateway’s MAC address. The attacker then intercepts traffic intended for the Cockroachdb node, potentially capturing authentication credentials or query metadata if encryption in transit is not enforced.

In practice, a Fastapi service connects to Cockroachdb using a connection string that includes a hostname or IP. If an attacker successfully spoofs the address of that hostname or IP, and the application does not enforce strict certificate or hostname verification, the client may unknowingly establish a TLS session with the attacker. Cockroachdb supports TLS with client certificates; without enforcing require_and_verify_client_cert or using a strict CA, a Fastapi app using a relaxed SSL context can be tricked into communicating with a malicious node. This exposes the authentication handshake and any metadata in the clear, depending on driver behavior and TLS configuration.

The exposure is compounded when Fastapi services perform unencrypted health checks or use default ports without network-level protections. Because middleBrick tests the unauthenticated attack surface, it flags weak transport configurations and missing host verification as high-severity findings. The scanner does not assume the database is internal; it probes reachable endpoints and evaluates whether encryption and identity checks are properly enforced, highlighting gaps that make spoofing attacks impactful in this specific stack.

Remediation centers on enforcing strong TLS, verifying server identity, and isolating the database network. Below are concrete, working examples for a Fastapi application connecting to Cockroachdb with secure settings.

import ssl
from fastapi import Fastapi, Depends
from sqlalchemy import text
from sqlalchemy.ext.declarative import DeclarativeMeta, DeclarativeBase
from sqlalchemy.orm import sessionmaker, Session
from sqlalchemy import create_engine

class Base(DeclarativeBase):
    pass

# Configure SSL context with strict verification
ssl_context = ssl.create_default_context(cafile="/path/to/ca.pem")
ssl_context.verify_mode = ssl.CERT_REQUIRED
ssl_context.check_hostname = True
ssl_context.load_cert_chain(
    certfile="/path/to/client.pem",
    keyfile="/path/to/client.key"
)

# Example connection string with SSL mode verify-full
DATABASE_URL = (
    "cockroachdb://:@:/?"
    "sslmode=verify-full&"
    "sslrootcert=/path/to/ca.pem&"
    "sslcert=/path/to/client.pem&"
    "sslkey=/path/to/client.key"
)

engine = create_engine(
    DATABASE_URL,
    connect_args={"ssl": ssl_context},
    pool_pre_ping=True
)

SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

def get_db():
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()

app = Fastapi()

@app.get("/health")
def health(db: Session = Depends(get_db)):
    result = db.execute(text("SELECT cluster_id, node_id FROM crdb_internal.node_cluster_id LIMIT 1"))
    row = result.fetchone()
    return {"cluster_id": row[0], "node_id": row[1] if row else None}

@app.get("/users/{user_id}")
def read_user(user_id: int, db: Session = Depends(get_db)):
    result = db.execute(text("SELECT username, email FROM users WHERE id = :id"), {"id": user_id})
    row = result.fetchone()
    if row is None:
        raise HTTPException(status_code=404, detail="User not found")
    return {"username": row[0], "email": row[1]}

Key practices:

• Use sslmode=verify-full and provide a trusted CA certificate to prevent accepting spoofed certificates.
• Set check_hostname=True so the driver validates the hostname in the server certificate against the connection target.
• Enforce client certificate authentication by configuring ssl_context with CERT_REQUIRED and loading client cert/key.
• Restrict network access to the Cockroachdb nodes using firewall rules or VPC peering so that ARP spoofing is limited to trusted subnets.
• Rotate certificates regularly and avoid default ports in exposed environments; prefer non-standard ports combined with IP whitelisting.

These steps align with middleBrick’s findings around encryption, authentication, and transport security, ensuring that even if an attacker attempts ARP spoofing, the integrity and confidentiality of the Cockroachdb connection remain intact.