Http Request Smuggling in Chi with Mongodb

Http Request Smuggling occurs when an application processes HTTP requests differently in transit versus at the backend, allowing attackers to smuggle requests across security boundaries. In Chi, a common Go HTTP router, this risk arises when request parsing and routing are not strictly aligned with how an upstream proxy or load balancer terminates connections. When combined with MongoDB as the backend data store, smuggling can expose sensitive records or enable unauthorized write operations if requests are routed to the wrong handler based on malformed headers or body handling.

Chi’s middleware stack relies heavily on explicit route definitions and handlers. If developers inadvertently allow the request body to be read multiple times or fail to enforce strict content-length and transfer-encoding validation, an attacker can craft requests where the proxy consumes the body differently than Chi’s downstream handlers. For example, a request might be split so that one version reaches the public-facing handler (e.g., a search endpoint) and another reaches an administrative handler (e.g., a user update endpoint), with MongoDB operations tied to the latter. Because MongoDB operations in Chi are typically invoked only after routing decisions, smuggling can bypass intended access controls, leading to unauthorized data access or modification. This becomes especially critical when MongoDB queries are constructed from parsed request parameters that should have been isolated to authenticated administrative routes.

The unauthenticated attack surface that tools like middleBrick test is relevant here: a scanner can probe Chi endpoints with malformed headers and inconsistent message lengths to detect inconsistent routing behavior. If a Chi service parses requests loosely and passes user-supplied input directly into MongoDB queries without strict validation, smuggling vectors may allow attackers to execute unintended queries. For instance, a request smuggled via the Content-Length and Transfer-Encoding headers might reach a handler that performs a MongoDB Find using an ID supplied in the body, exposing data that should remain restricted. middleBrick’s checks for BOLA/IDOR and Input Validation are designed to surface such inconsistencies by correlating spec definitions from OpenAPI documents with runtime behavior, including how parameters are used in MongoDB operations.

In practice, ensuring that Chi routes are strict about body ownership and that MongoDB queries are scoped to the intended tenant or user context is essential. Middleware that normalizes headers before routing, rejects ambiguous messages, and binds request context explicitly to MongoDB query filters reduces the surface area for smuggling. Continuous scanning with middleBrick, particularly its OpenAPI/Swagger analysis with full $ref resolution, can highlight mismatches between documented routes and actual handler behavior, helping teams identify where smuggling might intersect with MongoDB data access patterns.

Remediation focuses on aligning request parsing, routing, and MongoDB access in Chi. Use explicit middleware to validate headers, reject requests with both Content-Length and Transfer-Encoding, and ensure only one body reader is used. Scope all MongoDB queries with tenant or user context derived from authenticated session data rather than from potentially smuggled request parameters.

1. Strict header validation and body handling

Add middleware that rejects ambiguous messages before routing. For example:

import "net/http"
import "github.com/go-chi/chi/v5"
import "github.com/go-chi/chi/v5/middleware"

func secureMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // Reject requests that contain both Transfer-Encoding and Content-Length
        if r.TransferEncoding != nil && r.Header.Get("Content-Length") != "" {
            http.Error(w, "invalid headers", http.StatusBadRequest)
            return
        }
        // Ensure body is read only once
        r.Body = http.MaxBytesReader(w, r.Body, 10<<20) // 10 MB limit
        next.ServeHTTP(w, r)
    })
}

func main() {
    r := chi.NewRouter()
    r.Use(middleware.RequestID)
    r.Use(middleware.RealIP)
    r.Use(secureMiddleware)
    // routes here
}

2. Scoped MongoDB queries with validated context

Use Chi’s route context to pass authenticated user information into MongoDB queries. Avoid using raw request parameters for tenant or user identification without validation.

import "go.mongodb.org/mongo-driver/mongo"
import "go.mongodb.org/mongo-driver/bson"
import "net/http"

func getUserProfile(client *mongo.Client) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        userID := r.Context().Value("user_id").(string) // authenticated identity
        collection := client.Database("appdb").Collection("users")
        var profile bson.M
        err := collection.FindOne(r.Context(), bson.D{{"_id", userID}}).Decode(&profile)
        if err != nil {
            http.Error(w, "not found", http.StatusNotFound)
            return
        }
        // respond with profile
    }
}

3. Reject smuggling-prone content encodings

Disable chunked transfer encoding for handlers that interact with MongoDB unless strictly required, and normalize input to prevent header-based confusion.

func noChunkedMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        if r.Header.Get("Transfer-Encoding") == "chunked" {
            http.Error(w, "chunked encoding not allowed", http.StatusBadRequest)
            return
        }
        next.ServeHTTP(w, r)
    })
}

Combine these patterns and validate all inputs against an OpenAPI spec before constructing MongoDB queries. This reduces the risk that smuggled requests alter the intended database operations.