Privilege Escalation in Buffalo

Privilege escalation (also called Broken Function Level Authorization, or BFLA) occurs when an attacker can access functions or resources that should be restricted to a higher privilege level. In Buffalo applications, this vulnerability commonly arises from two patterns: insufficient authorization checks on endpoints and over-permissive parameter binding.

Attack Pattern 1: Unchecked Role Assignment
Buffalo's c.Bind automatically maps JSON request bodies to Go structs. If a struct includes sensitive fields like Role or IsAdmin, an attacker can simply include these in the request to elevate their privileges. For example, a vulnerable user update endpoint might look like this:

type User struct {
    ID        uuid.UUID `json:"id"`
    Name      string    `json:"name"`
    Email     string    `json:"email"`
    Role      string    `json:"role"` // Dangerous: user-controlled
}

func UpdateUser(c buffalo.Context) error {
    user := &models.User{}
    if err := c.Bind(user); err != nil {
        return c.Error(400, err)
    }
    // No check if current user can change role!
    return c.Render(200, r.JSON(user))
}

An attacker can send {"id": "...", "role": "admin"} and become an admin.

Attack Pattern 2: Insecure Direct Object Reference (IDOR) Leading to Escalation
Buffalo often uses c.Param to fetch resource IDs from the URL. If the code doesn't verify that the authenticated user has permission to access the requested resource, an attacker can access or modify others' data. For instance:

func ShowAdminNote(c buffalo.Context) error {
    id := c.Param("id")
    note := &models.Note{}
    // No check: any authenticated user can fetch any note!
    if err := DB.Find(note, id); err != nil {
        return c.Error(404, err)
    }
    return c.Render(200, r.JSON(note))
}

Even if the route is restricted to logged-in users (c.Auth), any user can view admin notes by ID guessing.

Buffalo-Specific Nuance: Buffalo's c.Auth middleware only ensures authentication, not authorization. Developers often mistakenly assume that c.Auth also enforces that users can only act on their own data. Additionally, Buffalo's automatic binding to entire structs (rather than specific fields) makes it easy to accidentally expose sensitive fields.

Detecting privilege escalation in Buffalo requires examining both code patterns and runtime behavior.

Code Review Indicators:

• Look for c.Bind calls that bind to structs containing fields like Role, Permissions, IsAdmin, or UserID (when the user shouldn't set these).
• Check endpoints that use c.Param("id") or c.Query("id") to fetch resources without subsequent authorization logic (e.g., comparing note.UserID to c.CurrentUserID()).
• Verify that after c.Auth, there is explicit permission checking (role checks, ownership checks) before performing actions.

Runtime Scanning with middleBrick:
middleBrick's BFLA/Privilege Escalation check actively probes Buffalo APIs. It works by:

• Authenticating (if possible) to obtain a low-privilege token.
• Sending crafted requests that attempt to change roles (e.g., adding "role":"admin" to JSON payloads) or access resources belonging to other users (by modifying IDs in URLs).
• Analyzing responses: if the server returns 200 OK and applies the elevated privilege (e.g., the response includes admin fields, or the resource is modified), it flags a vulnerability.

For a Buffalo API, middleBrick will test all endpoints that accept POST/PUT/PATCH/DELETE and endpoints with ID parameters. The scan takes 5–15 seconds and produces a per-category breakdown with severity ratings. For example, a finding might read: "BFLA: User role updatable without authorization check" with a CWE reference (e.g., CWE-639) and remediation guidance.

Manual Testing Steps:

1. Identify authenticated endpoints (those behind c.Auth).
2. For update endpoints, try adding privilege-related fields to the JSON body.
3. For resource endpoints with IDs, try accessing IDs belonging to other users (e.g., change /users/me/notes/1 to /users/me/notes/2).

Fix privilege escalation in Buffalo by applying the principle of least privilege at the binding and authorization layers.

1. Use Separate Binding Structs
Never bind directly to your full model struct for updates. Instead, create a params struct that only includes fields the user is allowed to set. Buffalo's c.Bind works with any struct, so define:

type UpdateUserParams struct {
    Name  string `json:"name"`
    Email string `json:"email"`
    // Note: no Role field!
}

func UpdateUser(c buffalo.Context) error {
    params := &UpdateUserParams{}
    if err := c.Bind(params); err != nil {
        return c.Error(400, err)
    }
    user := c.CurrentUser() // from c.Auth
    user.Name = params.Name
    user.Email = params.Email
    // Role is never updated here
    DB.Update(user)
    return c.Render(200, r.JSON(user))
}

This prevents mass assignment of sensitive fields.

2. Enforce Ownership or Role Checks
For any endpoint that acts on a specific resource, verify that the current user has the right to access it. Buffalo provides c.CurrentUserID() (or c.CurrentUser() if you set it in the auth middleware). Example for a notes endpoint:

func ShowNote(c buffalo.Context) error {
    noteID := c.Param("note_id")
    note := &models.Note{}
    if err := DB.Find(note, noteID); err != nil {
        return c.Error(404, err)
    }
    // Authorization check: user must own the note or be admin
    currentUserID := c.CurrentUserID()
    if note.UserID != currentUserID && !c.CurrentUser().IsAdmin {
        return c.Error(403, errors.New("forbidden"))
    }
    return c.Render(200, r.JSON(note))
}

3. Use Buffalo's Authorize Middleware
For complex authorization, create a custom middleware that runs after c.Auth. For example, an RequireRole middleware:

func RequireRole(role string) buffalo.MiddlewareFunc {
    return func(next buffalo.Handler) buffalo.Handler {
        return func(c buffalo.Context) error {
            user := c.CurrentUser()
            if user == nil || user.Role != role {
                return c.Error(403, errors.New("forbidden"))
            }
            return next(c)
        }
    }
}

// In routes:
// app.GET("/admin", AdminHandler, RequireRole("admin"))

4. Validate Input for Authorization Context
Even with binding structs, validate that the user isn't trying to manipulate IDs. Use Buffalo's validation to ensure that, for example, a user_id parameter matches the current user (unless the user is an admin).

By combining these patterns, you ensure that Buffalo applications do not inadvertently grant escalated privileges. Remember: authentication (via c.Auth) is only the first step; every endpoint must explicitly authorize the action.