refactor: update authentication error handling to prevent user enumeration and improve error messages

surfsense_backend/app/app.py

@@ -62,7 +62,7 @@ def _rate_limit_exceeded_handler(request: Request, exc: RateLimitExceeded):
 # ============================================================================
 # Stricter per-IP limits on auth endpoints to prevent:
 # - Brute force password attacks
-# - User enumeration via LOGIN_USER_NOT_FOUND / REGISTER_USER_ALREADY_EXISTS
+# - User enumeration via REGISTER_USER_ALREADY_EXISTS
 # - Email spam via forgot-password
 #
 # These use direct Redis INCR+EXPIRE for simplicity and reliability.

surfsense_backend/app/users.py

@@ -2,7 +2,7 @@ import logging
 import uuid
 
 import httpx
-from fastapi import Depends, HTTPException, Request, Response
+from fastapi import Depends, Request, Response
 from fastapi.responses import JSONResponse, RedirectResponse
 from fastapi_users import BaseUserManager, FastAPIUsers, UUIDIDMixin, models
 from fastapi_users.authentication import (
@@ -47,6 +47,14 @@ if config.AUTH_TYPE == "GOOGLE":
 
 
 class UserManager(UUIDIDMixin, BaseUserManager[User, uuid.UUID]):
+    """
+    Custom user manager extending fastapi-users BaseUserManager.
+
+    Authentication returns a generic error for both non-existent accounts
+    and incorrect passwords to comply with OWASP WSTG-IDNT-04 and
+    prevent user enumeration attacks.
+    """
+
     reset_password_token_secret = SECRET
     verification_token_secret = SECRET
 
@@ -180,36 +188,6 @@ class UserManager(UUIDIDMixin, BaseUserManager[User, uuid.UUID]):
     ):
         print(f"Verification requested for user {user.id}. Verification token: {token}")
 
-    async def authenticate(self, credentials):
-        """
-        Override to return a specific error when user account doesn't exist,
-        instead of a generic LOGIN_BAD_CREDENTIALS.
-        """
-        from fastapi_users.exceptions import UserNotExists
-
-        try:
-            user = await self.get_by_email(credentials.username)
-        except UserNotExists:
-            # Still hash the password to mitigate timing attacks
-            self.password_helper.hash(credentials.password)
-            logger.warning(
-                f"Login attempt for non-existent account: {credentials.username}"
-            )
-            raise HTTPException(
-                status_code=400,
-                detail="LOGIN_USER_NOT_FOUND",
-            ) from None
-
-        verified, updated_password_hash = self.password_helper.verify_and_update(
-            credentials.password, user.hashed_password
-        )
-        if not verified:
-            logger.warning(f"Failed login attempt (wrong password) for user: {user.id}")
-            return None
-        if updated_password_hash is not None:
-            await self.user_db.update(user, {"hashed_password": updated_password_hash})
-        return user
-
 
 async def get_user_manager(user_db: SQLAlchemyUserDatabase = Depends(get_user_db)):
     yield UserManager(user_db)

surfsense_web/lib/auth-errors.ts

@@ -20,8 +20,8 @@ const AUTH_ERROR_MESSAGES: AuthErrorMapping = {
 		description: "Your account may be suspended or restricted",
 	},
 	"404": {
-		title: "Account not found",
+		title: "Not found",
-		description: "No account exists with this email address",
+		description: "The requested resource was not found",
 	},
 	"409": {
 		title: "Account conflict",
@@ -46,12 +46,8 @@ const AUTH_ERROR_MESSAGES: AuthErrorMapping = {
 
 	// FastAPI specific errors
 	LOGIN_BAD_CREDENTIALS: {
-		title: "Invalid credentials",
+		title: "Login failed",
-		description: "The email or password you entered is incorrect",
+		description: "Invalid email or password. If you don't have an account, please sign up.",
-	},
-	LOGIN_USER_NOT_FOUND: {
-		title: "Account not found",
-		description: "No account exists with this email address. Please sign up first.",
 	},
 	LOGIN_USER_NOT_VERIFIED: {
 		title: "Account not verified",
@@ -147,10 +143,6 @@ export function getAuthErrorMessage(errorCode: string, returnTitle: boolean = fa
 	if (!errorInfo) {
 		const patterns = [
 			{ pattern: /credential|password|email/i, code: "LOGIN_BAD_CREDENTIALS" },
-			{
-				pattern: /not found|no account|does not exist|user not found/i,
-				code: "LOGIN_USER_NOT_FOUND",
-			},
 			{ pattern: /verify|verification/i, code: "LOGIN_USER_NOT_VERIFIED" },
 			{ pattern: /inactive|disabled|suspended/i, code: "USER_INACTIVE" },
 			{ pattern: /exists|duplicate/i, code: "REGISTER_USER_ALREADY_EXISTS" },