Cross Site Request Forgery in Gorilla Mux with Mongodb

Cross Site Request Forgery (CSRF) in a Gorilla Mux service that uses MongoDB arises when state-changing HTTP requests (POST, PUT, PATCH, DELETE) rely only on cookies for session identity and do not verify the request origin or include a user-specific token. Gorilla Mux is a request router and matcher; it does not enforce authentication or CSRF protections by itself. If your application stores session or user identifiers in cookies and uses MongoDB to fetch or update user data based on those cookies, an attacker can trick a logged-in user into submitting a crafted request that the router forwards to a MongoDB-backed handler.

Consider a handler registered with mux.NewRouter() and a MongoDB collection users. If the handler reads userID from a cookie and directly builds a filter like bson.M{"_id": userID} to update profile data, there is no check that the requesting user owns the targeted resource. An attacker can host a malicious page with a form that points to your endpoint (e.g., /profile) and trigger image or script requests from the victim’s browser. Because the browser includes cookies automatically, the request reaches your Gorilla Mux router, passes the cookie-based user identification, and executes the update in MongoDB on behalf of the victim.

Additionally, if your OpenAPI spec (used by middleBrick for spec-runtime cross-referencing) describes endpoints with cookie-based auth but omits anti-CSRF guidance, the unauthenticated attack surface tested by middleBrick can surface routes where CSRF is plausible. middleBrick scans 12 checks in parallel, including Authentication and Property Authorization, to highlight cases where cookie-based sessions intersect with mutating MongoDB operations without verifiable request integrity controls.

Remediation focuses on ensuring each state-changing request in Gorilla Mux is tied to the authenticated user in a way that cannot be forged by a third-party site, and that MongoDB operations validate ownership explicitly.

• Use anti-CSRF tokens for state-changing methods. Store a per-session random token in a server-side session store or in an HttpOnly, SameSite=Strict cookie, and require it in a header or form field for mutating requests. Gorilla Mux can extract the token from headers before routing to the handler.
• Always resolve the user identity from the session or token, not from client-supplied parameters, and enforce ownership in MongoDB filters. Avoid using raw cookie values to build MongoDB selectors without server-side verification.
• Set SameSite cookie attributes and consider Secure and HttpOnly flags to reduce the attack surface available to browser-based forgery.

Example secure handler with CSRF token validation and strict MongoDB ownership checks:

// Assume a valid store providing GetSession and SaveSession methods
func ProfileUpdate(store SessionStore, client *mongo.Client) http.HandlerFunc {
    collection := client.Database("app").Collection("users")
    return func(w http.ResponseWriter, r *http.Request) {
        session, err := store.GetSession(r)
        if err != nil || session.UserID == "" {
            http.Error(w, "unauthorized", http.StatusUnauthorized)
            return
        }

        // Validate anti-CSRF token from header
        reqToken := r.Header.Get("X-CSRF-Token")
        if reqToken == "" || reqToken != session.CSRFToken {
            http.Error(w, "invalid csrf token", http.StatusForbidden)
            return
        }

        var payload struct {
            Email string `json:"email"`
        }
        if err := json.NewDecoder(r.Body).Decode(&payload); err != nil {
            http.Error(w, "bad request", http.StatusBadRequest)
            return
        }

        // Enforce ownership in MongoDB using the session-derived userID
        filter := bson.M{"_id": session.UserID}
        update := bson.M{"$set": bson.M{"email": payload.Email}}
        result, err := collection.UpdateOne(r.Context(), filter, update)
        if err != nil || result.MatchedCount == 0 {
            http.Error(w, "update failed", http.StatusInternalServerError)
            return
        }

        w.WriteHeader(http.StatusOK)
        w.Write([]byte(`{"ok":true}`))
    }
}

Register the handler with Gorilla Mux and require the CSRF token on non-GET methods:

r := mux.NewRouter()
r.HandleFunc("/profile", ProfileUpdate(store, mongoClient)).Methods("POST", "PUT", "PATCH")
// For GET, token validation can be omitted if no state change occurs
r.HandleFunc("/profile", GetProfile(mongoClient)).Methods("GET")

In addition, if you use middleBrick’s CLI to scan from terminal (middlebrick scan <url>) or integrate the GitHub Action to add API security checks to your CI/CD pipeline, you can detect endpoints where CSRF-prone patterns intersect with MongoDB mutating operations and prioritize fixes based on the provided severity and remediation guidance.