Integrity Failures in Fastapi with Basic Auth

Integrity failures occur when an attacker can alter data in transit or cause a server to process invalid or malicious data. In FastAPI applications that rely solely on HTTP Basic Authentication, the risk of integrity issues is heightened because the mechanism itself does not prevent tampering. Basic Auth sends credentials as a base64-encoded string rather than an encrypted value; while not inherently insecure when used over TLS, it provides no built-in message integrity checks.

Without additional protections such as request signing or transport-layer integrity guarantees, an attacker who can observe or modify network traffic may alter the Authorization header or the request payload. Because FastAPI processes requests based on the presence and correctness of the header, an altered token or impersonated username can lead to privilege escalation or unauthorized data modification. For example, an attacker who changes the username in a Basic Auth header might be treated as a different user if authorization logic relies solely on header parsing rather than verifying a session or token signature.

When OpenAPI specifications are parsed by middleBrick, definitions that reference Basic Auth security schemes are cross-referenced with runtime behavior. If the spec declares security requirements but the implementation does not enforce integrity checks (e.g., missing HTTPS or lack of request validation), findings are surfaced with severity and remediation guidance. In an unauthenticated scan, middleBrick can detect whether endpoints exposed under Basic Auth also enforce transport security and validate input, helping identify integrity risks tied to authentication misuse.

Consider a FastAPI endpoint that accepts a JSON body to update a user profile. If the request relies only on Basic Auth for identification and does not verify that the requesting user is allowed to modify the target resource, an attacker can change the username in the header and modify another user’s data. This maps to BOLA/IDOR and Integrity Failure categories in the 12 parallel checks. middleBrick’s OpenAPI/Swagger analysis resolves $ref security schemes and compares them to runtime tests, surfacing cases where transport protections are assumed but not verified.

LLM/AI Security checks performed by middleBrick are not designed to protect Basic Auth flows, but they do highlight how untrusted inputs and exposed endpoints can lead to broader compromise. For instance, if an API also exposes an LLM endpoint without authentication, output scanning would look for credentials or PII in responses. While Basic Auth itself is not an LLM vector, combining weak authentication patterns with insufficient input validation can amplify risks across the API surface. The scanner’s detection of insecure authentication schemes complements the integrity checks by emphasizing the need for signed requests or additional validation layers.

Remediation focuses on ensuring that credentials are not relied upon for integrity and that requests are validated server-side. Always serve FastAPI applications over HTTPS to protect credentials in transit and to prevent on-path modification of the Authorization header. Basic Auth should be treated as a weak identifier and never used as the sole mechanism for authorization or integrity.

Use middleware or dependency injection to validate the contents of requests beyond the presence of a Basic Auth header. For example, require an additional token or signed session for critical operations, and verify permissions against a backend store rather than trusting the username presented in the header. Combine Basic Auth with request signing for sensitive endpoints, where a signature is computed over key parts of the payload and verified before processing.

Below are concrete FastAPI code examples illustrating secure patterns. The first shows a standard Basic Auth dependency that validates credentials against a user store. The second demonstrates how to layer an additional integrity check using a signed payload or custom header for sensitive routes.

from fastapi import Depends, FastAPI, HTTPException, status
from fastapi.security import HTTPBasic, HTTPBasicCredentials
import secrets

app = FastAPI()
security = HTTPBasic()

# Mock user store
USERS = {
    "alice": {"password": "strongpassword", "role": "user"},
    "admin": {"password": "adminsecret", "role": "admin"},
}

def get_current_user(credentials: HTTPBasicCredentials = Depends(security)):
    user = USERS.get(credentials.username)
    if user is None or user["password"] != credentials.password:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Incorrect username or password",
            headers={"WWW-Authenticate": "Basic"},
        )
    return credentials.username

@app.get("/profile")
def read_profile(username: str = Depends(get_current_user)):
    # In a real app, fetch profile for `username` from a database
    return {"username": username, "data": "safe profile"}

This pattern correctly rejects invalid credentials but still does not protect against tampering of the request body. To address integrity, introduce a per-request token or signature for state-changing operations:

from fastapi import Header, HTTPException
import hashlib
import hmac

SECRET = b"super-secret-key"

def verify_signature(x_signature: str = Header(...), payload: str = ""):
    expected = hmac.new(SECRET, payload.encode(), hashlib.sha256).hexdigest()
    if not hmac.compare_digest(expected, x_signature):
        raise HTTPException(status_code=400, detail="Invalid signature")

@app.post("/update")
def update_profile(
    username: str = Depends(get_current_user),
    x_signature: str = Header(...),
    body: dict = {},
):
    # Serialize the body in a canonical way for verification
    payload = str(sorted(body.items()))
    verify_signature(x_signature=x_signature, payload=payload)
    # Proceed with update logic
    return {"status": "updated"}

In production, use standard libraries for signing and verification, rotate keys, and ensure TLS is enforced at the load balancer or server level. middleBrick’s scans can highlight whether endpoints using Basic Auth also show missing integrity controls, enabling teams to prioritize fixes.