Clickjacking in Fiber with Api Keys

Clickjacking is a client-side attack that tricks a user into interacting with a hidden or disguised UI element inside an embedded frame. When an API protected by Api Keys is served from a Fiber endpoint and rendered inside an attacker-controlled page, the combination can expose interactive endpoints to unauthorized actions. Fiber does not set restrictive framing headers by default, so a response intended for an embedded context can be displayed in a frame on a malicious site.

Consider a Fiber endpoint that performs a sensitive operation using an Api Key passed via a header. If the response is also served with an absent or permissive X-Frame-Options or Content-Security-Policy frame-ancestors directive, an attacker can embed the endpoint in an <iframe> and overlay invisible controls or misleading UI on top of it. The user, authenticated via session or token and unknowingly interacting with the attacker’s page, may trigger the embedded endpoint. Because the request includes valid Api Key headers, the action is authorized from the server’s perspective, even though the user did not intend to perform it.

This scenario is distinct from traditional CSRF because the authorization mechanism is an Api Key header rather than a cookie. However, if the Api Key is stored in browser storage or injected into requests by a client-side framework, the browser will include it automatically when the endpoint is loaded in a frame. The attack surface is compounded when the endpoint returns a response that is meaningful in an embedded context, such as an action confirmation or a UI component that can be manipulated via query parameters. The server-side detection performed by middleBrick identifies this risk when a response that uses Api Key authorization can be rendered inside a frame, surfacing the missing frame-ancestors directive and advising on CSP or X-Frame-Options to mitigate the exposure.

To remediate clickjacking for endpoints using Api Keys in Fiber, apply frame-ancestors restrictions and ensure that sensitive responses are not embeddable. Below are two concrete Fiber examples: one insecure baseline and one corrected implementation.

Insecure endpoint with Api Key header

// Insecure: no framing protections, Api Key validated but response can be embedded
app.Get("/transfer", func(c *fiber.Ctx) error {
    apiKey := c.Get("X-API-Key")
    if !isValidKey(apiKey) {
        return c.Status(fiber.StatusUnauthorized).JSON(fiber.Map{"error": "invalid api key"})
    }
    // performs sensitive action
    return c.JSON(fiber.Map{"status": "transfer initiated"})
})

func isValidKey(key string) bool {
    // simplistic validation for example
    return key == "SECRET_123"
}

Secured endpoint with Content-Security-Policy frame-ancestors

// Secured: strict CSP prevents embedding, Api Key authorization retained
app.Get("/transfer", func(c *fiber.Ctx) error {
    apiKey := c.Get("X-API-Key")
    if !isValidKey(apiKey) {
        return c.Status(fiber.StatusUnauthorized).JSON(fiber.Map{"error": "invalid api key"})
    }
    // set CSP header to disallow framing
    c.Set("Content-Security-Policy", "frame-ancestors 'none'")
    return c.JSON(fiber.Map{"status": "transfer initiated"})
})

func isValidKey(key string) bool {
    return key == "SECRET_123"
}

Alternatively, use X-Frame-Options where CSP is not feasible:

c.Set("X-Frame-Options", "DENY")

These changes ensure that even if an Api Key is presented, the response cannot be embedded in a hostile frame. middleBrick’s scan will flag the missing frame-ancestors directive when it detects Api Key usage and serving embeddable responses, providing remediation guidance aligned with OWASP API Top 10 and Content Security Policy best practices.