Integrity Failures in Buffalo with Mongodb

An Integrity Failure in the context of API security occurs when an attacker can read, modify, create, or delete data that should be restricted. In Buffalo applications using Mongodb, this often maps to the BOLA/IDOR and BFLA/Privilege Escalation checks in middleBrick’s 12-test suite. Buffalo’s convention-based routing and parameter handling can inadvertently expose object identifiers and business logic that do not enforce ownership or role checks at the data layer.

When a Buffalo endpoint accepts an :id parameter and directly uses it to construct a Mongodb query without verifying that the authenticated subject owns that document, an IDOR path is created. For example, a route like GET /invoices/:id might call an Invoice model that does a find by ID in Mongodb without scoping the query to the current user’s tenant or ID. Because Mongodb queries are straightforward maps, supplying an attacker-controlled ID returns data if it exists, regardless of business permissions.

Buffalo’s HTML templates and form handling may also contribute when developers bind user input directly to update operations without validating field-level authorization. A PATCH /invoices/:id that accepts a payload with an is_admin flag and passes the entire params map into a Mongodb $set can allow privilege escalation if the server applies updates without stripping or validating sensitive keys. This is a BFLA pattern: a lower-privilege action (e.g., updating an invoice status) leads to unauthorized attribute changes (is_admin) because the server trusted client input for field-level permissions.

Mongodb’s flexible schema amplifies these risks. Without schema-enforced constraints, it is easy for a developer to query on a field like user_id only in some routes and omit it in others. In a Buffalo app, inconsistent query scoping across handlers means an attacker can leverage an otherwise “safe” endpoint to infer data existence or traverse relationships via ObjectId references. middleBrick’s BOLA/IDOR and BFLA/Privilege Escalation checks detect these patterns by correlating spec definitions (where parameters are declared) with runtime behavior (what queries are executed and what fields are returned or accepted).

Additionally, if the Buffalo app exposes a GraphQL or JSON:API layer over Mongodb, resolvers that do not enforce ownership checks become direct vectors. A query that returns all invoices for a given project ID without validating project membership enables data leakage. middleBrick’s Property Authorization checks examine whether returned fields are properly gated, ensuring sensitive fields like role flags or financial totals are not disclosed when they should be restricted.

To contextualize findings, middleBrick maps results to frameworks such as OWASP API Top 10 (2023), where Integrity Failures commonly appear under Broken Object Level Authorization and Broken Function Level Authorization. PCI-DSS and SOC2 also require strict data access controls; a failure here can be a significant compliance gap. By scanning with middleBrick, teams receive prioritized findings with severity, a per-category breakdown, and remediation guidance that includes concrete code changes to enforce scoping and input validation in Buffalo applications using Mongodb.

Remediation focuses on ensuring every Mongodb query in a Buffalo app is scoped to the authenticated subject and that updates validate and sanitize all fields. Below are concrete, working code examples for Buffalo handlers using the official MongoDB Go driver.

1) Scope reads by user_id

Always include a tenant or user identifier in the filter. Do not rely on the :id alone.

// Good: scope by user_id and validate ownership before returning data
func InvoicesShow(c buffalo.Context) error {
    userID, _ := c.Value(&sessionKey).(*models.User).ID // assume session provides user
    id := c.Params().Get("id")
    filter := bson.D{{"_id", id}, {"user_id", userID}}
    var inv models.Invoice
    if err := c.Value("db").(*mongo.Collection).FindOne(c.Request().Context(), filter).Decode(&inv); err != nil {
        return c.Render(404, r.JSON(Error{Message: "not found"}))
    }
    return c.Render(200, r.JSON(inv))
}

2) Reject unauthorized field updates

Strip or reject fields that should not be client-controllable, and enforce server-side permissions.

// Good: explicitly allow safe fields and remove sensitive ones
func InvoicesUpdate(c buffalo.Context) error {
    userID, _ := c.Value(&sessionKey).(*models.User).ID
    id := c.Params().Get("id")

    // Ensure the invoice belongs to the user before updating
    var tmp models.Invoice
    coll := c.Value("db").(*mongo.Collection)
    filter := bson.D{{"_id", id}, {"user_id", userID}}
    if err := coll.FindOne(c.Request().Context(), filter).Decode(&tmp); err != nil {
        return c.Render(403, r.JSON(Error{Message: "forbidden"}))
    }

    var payload map[string]interface{}
    if err := c.Bind(&payload); err != nil {
        return c.Render(400, r.JSON(Error{Message: "bad request"}))
    }

    // Remove fields that should never be user-updatable
    delete(payload, "is_admin")
    delete(payload, "role")
    delete(payload, "permissions")

    update := bson.D{{"$set", payload}}
    _, err := coll.UpdateOne(c.Request().Context(), filter, update)
    if err != nil {
        return c.Render(500, r.JSON(Error{Message: "update failed"}))
    }
    return c.Render(200, r.JSON(Map{"status": "ok"}))
}

3) Use MongoDB collation and schema rules where possible

While not a substitute for application logic, enforce uniqueness and constraints at the collection level to reduce invalid states.

// Example: ensure user_id is always present and indexed
_, err := c.Value("db").(*mongo.Collection).Indexes().CreateOne(
    context.TODO(),
    mongo.IndexModel{
        Keys: bson.D{{"user_id", 1}, {"id", 1}},
        Options: options.Index().SetUnique(true),
    },
)

4) Validate ObjectId formats before querying

Prevent injection-like issues by validating IDs to reduce unexpected behavior.

func isValidObjectID(id string) bool {
    _, err := primitive.ObjectIDFromHex(id)
    return err == nil
}

func InvoicesShow(c buffalo.Context) error {
    id := c.Params().Get("id")
    if !isValidObjectID(id) {
        return c.Render(400, r.JSON(Error{Message: "invalid id"}))
    }
    // continue with scoped query as shown earlier
}

5) Apply middleware to enforce tenant context

Use a Buffalo middleware to attach user context to the database calls, reducing duplication and ensuring scoping is consistent.

func UserMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // authenticate and attach user to context
        user, _ := authenticate(r)
        ctx := context.WithValue(r.Context(), &userKey, user)
        next.ServeHTTP(w, r.WithContext(ctx))
    })
}

By combining scoped queries, strict field validation, and consistent middleware, Buffalo + Mongodb apps can mitigate Integrity Failures. middleBrick’s scans help surface missing scoping and unsafe update patterns so teams can apply these patterns proactively.