Heartbleed in Fiber

Heartbleed in the context of Fiber applications typically occurs when developers use custom TLS/SSL implementations or expose TLS heartbeat functionality without proper validation. While Fiber itself doesn't have a built-in "heartbeat" endpoint like the original OpenSSL vulnerability, similar memory disclosure vulnerabilities can arise in Fiber applications that handle TLS connections or implement custom keep-alive mechanisms.

The most common Fiber-specific manifestation occurs when developers create custom health check endpoints or heartbeat handlers that read from request bodies without validating the length of the data. For example, a Fiber application might implement a health check like this:

app := fiber.New()

app.Post("/health", func(c *fiber.Ctx) error {
    length := c.Context().FormValue("length")
    data := make([]byte, length)
    c.Context().RequestBody(data)
    return c.JSON(fiber.Map{"status": "ok"})
})

This pattern is dangerous because if an attacker sends a length parameter larger than the actual request body, the server will read beyond the allocated buffer, potentially exposing sensitive memory contents. The vulnerability is particularly problematic in Go applications because the garbage collector may leave sensitive data (like database credentials, session tokens, or cryptographic keys) in memory that gets returned to the attacker.

Another Fiber-specific scenario involves improper handling of multipart form data in TLS contexts. When Fiber processes multipart uploads over TLS connections, memory management issues can expose adjacent memory if the content-length headers are manipulated:

app.Post("/upload", func(c *fiber.Ctx) error {
    // Vulnerable to memory exposure if content-length is manipulated
    file, err := c.FormFile("file")
    if err != nil {
        return err
    }
    
    // Process file without proper bounds checking
    return c.JSON(fiber.Map{"uploaded": true})
})

The risk is amplified in production Fiber applications that use connection pooling or keep-alive connections, as the same memory buffers may be reused across multiple requests, increasing the window of exposure for sensitive data.

Detecting Heartbleed-like vulnerabilities in Fiber applications requires a combination of static analysis and dynamic testing. The most effective approach is using middleBrick's automated scanning, which specifically tests for memory disclosure vulnerabilities in Go/Fiber applications.

middleBrick's scanner tests for these vulnerabilities by sending crafted requests with manipulated length parameters and oversized payloads to common Fiber endpoints. The scanner looks for patterns like:

middlebrick scan https://your-fiber-app.com

The scanner specifically tests for:

• Endpoints that accept length-prefixed data without validation
• Multipart form handlers that don't validate content-length headers
• Custom heartbeat or health check endpoints
• WebSocket upgrade handlers that may mishandle buffer allocation
• Streaming endpoints that read arbitrary amounts of data

During scanning, middleBrick sends requests with:

POST /health HTTP/1.1
Host: your-fiber-app.com
Content-Length: 1000000
Content-Type: application/x-www-form-urlencoded

length=999999

If the server responds with data that shouldn't be accessible or crashes in specific ways, this indicates a potential memory disclosure vulnerability. The scanner also analyzes the OpenAPI spec (if available) to identify endpoints that accept length parameters or binary data.

Manual detection techniques include:

// Use Fiber's built-in request size limits
app := fiber.New(fiber.Config{
    BodyLimit: 10 * 1024 * 1024, // 10MB limit
})

// Validate all input lengths
app.Post("/api/data", func(c *fiber.Ctx) error {
    length := c.FormValue("length")
    if length == "" {
        return c.Status(400).JSON(fiber.Map{"error": "length required"})
    }
    
    // Convert and validate
    lenVal, err := strconv.Atoi(length)
    if err != nil || lenVal < 0 || lenVal > 1024 {
        return c.Status(400).JSON(fiber.Map{"error": "invalid length"})
    }
    
    return c.JSON(fiber.Map{"status": "ok"})
})

Remediating Heartbleed-like vulnerabilities in Fiber applications requires a defense-in-depth approach. The first layer is proper input validation and bounds checking for all data that comes from external sources.

Here's a secure implementation of a health check endpoint:

app.Post("/health", func(c *fiber.Ctx) error {
    // Validate that length parameter exists and is within bounds
    lengthStr := c.FormValue("length")
    if lengthStr == "" {
        return c.Status(400).JSON(fiber.Map{"error": "length parameter required"})
    }
    
    length, err := strconv.Atoi(lengthStr)
    if err != nil || length < 0 || length > 1024 {
        return c.Status(400).JSON(fiber.Map{"error": "invalid length parameter"})
    }
    
    // Read only the exact amount of data requested
    body := c.Body()
    if len(body) < length {
        return c.Status(400).JSON(fiber.Map{"error": "body too short"})
    }
    
    // Process only the valid portion
    data := body[:length]
    
    // Return safe response
    return c.JSON(fiber.Map{"status": "ok", "length": length})
})

For multipart form handling, use Fiber's built-in validation:

app.Post("/upload", func(c *fiber.Ctx) error {
    // Set maximum upload size
    c.Context().SetBodyLimit(10 * 1024 * 1024) // 10MB
    
    // Validate file size before processing
    file, err := c.FormFile("file")
    if err != nil {
        return c.Status(400).JSON(fiber.Map{"error": "file upload failed"})
    }
    
    fileInfo, err := file.Open()
    if err != nil {
        return c.Status(500).JSON(fiber.Map{"error": "file open failed"})
    }
    defer fileInfo.Close()
    
    // Check file size
    stat, err := fileInfo.Stat()
    if err != nil || stat.Size() > 10*1024*1024 {
        return c.Status(400).JSON(fiber.Map{"error": "file too large"})
    }
    
    // Process file safely
    return c.JSON(fiber.Map{"uploaded": true, "size": stat.Size()})
})

For comprehensive protection, implement these additional measures:

app.Use(func(c *fiber.Ctx) error {
    // Set strict body limits for all requests
    c.Context().SetBodyLimit(1 * 1024 * 1024) // 1MB default limit
    
    // Validate content-length headers
    contentLength := c.Context().Request().Header.ContentLength()
    if contentLength > 1*1024*1024 {
        return c.Status(413).JSON(fiber.Map{"error": "payload too large"})
    }
    
    return c.Next()
})

// Use Fiber's middleware for additional security
app.Use(middleware.Compress())
app.Use(middleware.CORS())
app.Use(middleware.Fallback())

middleBrick's continuous monitoring can verify these fixes by regularly scanning your API endpoints and ensuring no memory disclosure vulnerabilities remain. The Pro plan's continuous monitoring will alert you if any new endpoints are added that might reintroduce these vulnerabilities.