Cross Site Request Forgery in Buffalo with Dynamodb

Cross Site Request Forgery (CSRF) in a Buffalo application that uses DynamoDB as a data store can arise when state-changing requests rely on session cookies for authentication without additional anti-CSRF mechanisms. In Buffalo, if routes that mutate resources (e.g., updating or deleting a DynamoDB item via a POST, PUT, or DELETE) are protected only by cookie-based sessions, an attacker can trick a logged-in user into submitting a crafted request to the vulnerable endpoint. Because DynamoDB does not enforce per-request origin checks, the backend may process the request as valid if the user’s session cookie is present and the request parameters are not validated in a CSRF-aware way.

Specifically, a Buffalo handler that deserializes form values directly into a DynamoDB update expression can be vulnerable if it does not verify the request origin or include a per-request token. For example, an endpoint like /items/:id that accepts PUT to update item attributes may rely on session authentication alone. An attacker can host a malicious page that submits a PUT to that endpoint with altered attributes, and if the user’s browser automatically includes the session cookie, the operation executes under their permissions. Because DynamoDB operations are performed server-side, the attacker does not need to understand the schema—only the endpoint and parameter names—to craft harmful updates (such as changing ownership flags or elevating permissions).

The exposure is compounded when the application uses predictable identifiers (e.g., sequential IDs) for DynamoDB keys and does not enforce per-user authorization checks. A handler that updates an item by ID without confirming that the authenticated user owns that item creates a vertical privilege escalation path. CSRF in this context does not require cross-origin reads of DynamoDB responses; it only requires the victim to perform an action the attacker can predict. The risk is realized when state-changing routes lack synchronizer tokens (CSRF tokens) or when the API is designed to accept requests solely based on cookies without SameSite cookie attributes or anti-CSRF headers.

Using the middleBrick scanner on such an endpoint would highlight missing CSRF protections among the findings, especially for methods that mutate data. The scanner checks for the presence of anti-CSRF defenses in unauthenticated attack surface testing and surfaces the issue with severity and remediation guidance. This is important because even with DynamoDB handling data storage securely, the web layer in Buffalo must ensure each request is intentional and tied to the correct user.

To mitigate CSRF in Buffalo when using DynamoDB, combine standard CSRF defenses with careful handling of DynamoDB operations. Use per-request CSRF tokens for state-changing routes, enforce strict SameSite cookie attributes, and ensure every DynamoDB mutation includes server-side authorization that validates the authenticated user’s permission on the specific item.

1) Include CSRF token in forms and validate on submit

Generate a CSRF token per session and include it in forms and AJAX headers. In Buffalo, you can store the token in the session and verify it in a before action.

// actions/app.go: generate token for forms
func (v ItemsValidator) CSRFToken(c buffalo.Context) error {
    token, _ := session.GetCSRF(c) // helper to get or generate token
    c.Set("csrf_token", token)
    return c.Render(200, r.H{"csrf_token": token})
}

// In your template:
// <input type="hidden" name="csrf_token" value="{{ .csrf_token }}">

// actions/items.go: verify token for mutating actions
func (v ItemsController) Update(c buffalo.Context) error {
    if err := c.ValidateCsrf(); err != nil {
        return c.Render(403, r.H{"error": "invalid csrf token"})
    }
    // proceed with DynamoDB update
    return c.Redirect(303, routes.ItemPath(c.Params("id")))
}

2) Enforce SameSite cookies and secure session handling

Configure session cookies with SameSite=Strict or Lax and mark them as Secure in production. This reduces the likelihood that the browser will send cookies in cross-origin requests.

// actions/app.go: session configuration
func app() *buffalo.App {
    app := buffalo.New(buffalo.Options{
        Env:         ENV,
        SessionStore: &sessions.CookieStore{},
    })
    app.Middleware.Use(session.Middleware(secureCookieOptions()))
    return app
}

func secureCookieOptions() sessions.Options {
    return sessions.Options{
        Path:     "/",
        MaxAge:   3600,
        HttpOnly: true,
        Secure:   true,   // set true in production with HTTPS
        SameSite: http.SameSiteStrictMode,
    }
}

3) Server-side ownership check with DynamoDB before mutating

Always verify that the authenticated user is authorized to modify the target DynamoDB item. Use a condition expression to ensure the user owns the item, preventing unauthorized updates even if CSRF is bypassed.

// models/item.go: update with ownership condition
func UpdateItem(db *dynamodb.DynamoDB, itemID, userID string, updates map[string]*dynamodb.AttributeValue) error {
    input := &dynamodb.UpdateItemInput{
        TableName: aws.String("Items"),
        Key: map[string]*dynamodb.AttributeValue{
            "id": {S: aws.String(itemID)},
        },
        UpdateExpression: aws.String("set #owner = :u, #status = :s"),
        ConditionExpression: aws.String("attribute_exists(id) AND #owner = :user"),
        ExpressionAttributeNames: map[string]*string{
            "#owner": aws.String("owner"),
            "#status": aws.String("status"),
        },
        ExpressionAttributeValues: map[string]*dynamodb.AttributeValue{
            ":u": {S: aws.String(userID)},
            ":s": {S: aws.String("active")},
            ":user": {S: aws.String(userID)},
        },
    }
    _, err := db.UpdateItem(input)
    return err
}

// handlers/items.go: handler using the model
func (v ItemsController) Update(c buffalo.Context) error {
    if err := c.ValidateCsrf(); err != nil {
        return c.Render(403, r.H{"error": "invalid csrf token"})
    }
    userID := c.CurrentUser().ID
    itemID := c.Params("id")
    updates := map[string]*dynamodb.AttributeValue{
        "status": {S: aws.String("completed")},
    }
    if err := models.UpdateItem(v.DB, itemID, userID, updates); err != nil {
        return c.Render(400, r.H{"error": err.Error()})
    }
    return c.Redirect(303, routes.ItemPath(itemID))
}

4) Use anti-CSRF tokens for JSON APIs and AJAX

For API endpoints, require a custom header (e.g., X-CSRF-Token) validated on the server. This prevents cross-origin sites from making authenticated requests via scripts.

// actions/api/items.go: validate header for API
func (v ItemsController) UpdateAPI(c buffalo.Context) error {
    token := c.Request().Header.Get("X-CSRF-Token")
    if token == "" || !session.ValidateCSRF(token) {
        return c.Render(403, r.H{"error": "missing or invalid csrf token"})
    }
    // process DynamoDB update
    return c.JSON(200, r.H{"status": "ok"})
}

These steps ensure that CSRF risks are addressed specifically within Buffalo’s request handling and DynamoDB operations, combining framework-level protections with DynamoDB conditional writes to enforce ownership and integrity.