Uninitialized Memory in Fiber with Basic Auth

Uninitialized memory in a Fiber-based application that uses HTTP Basic Authentication can expose sensitive information when memory previously used by the process is not cleared before reuse. In Go, when a handler reads credentials from the Authorization header, the underlying buffer that holds those bytes may retain data from prior requests if the handler does not explicitly overwrite it. This becomes a risk when the handler passes the credentials to a response writer, a logging routine, or an external library that inspects memory beyond the intended length.

Consider a typical Basic Auth setup in Fiber:

app.Get('/api/secure', func(c *fiber.Ctx) error {
    user, pass, ok := c.BasicAuth()
    if !ok {
        return c.Status(fiber.StatusUnauthorized).SendString('Unauthorized')
    }
    // Process credentials
    return c.JSON(fiber.Map{"user": user})
})

In this example, c.BasicAuth() decodes the header and returns strings derived from the request’s bytes. If the underlying byte slices are reused by the runtime and not zeroed, fragments of previous authentication data could remain. An attacker who can influence memory layout (for example, via side channels or by co-locating services) might infer usernames or passwords when uninitialized memory is later read and logged or returned in error messages.

The risk is compounded when responses include credentials accidentally, such as echoing the username in JSON without validating or sanitizing the source buffer. Logging the raw header or the decoded values without scrubbing increases the chance that sensitive data persists in logs or crash dumps. Because Fiber does not automatically clear buffers, developers must ensure credentials are handled in a way that prevents accidental exposure through uninitialized memory.

MiddleBrick scans can detect indicators of such exposure by analyzing the API surface, including how authentication data is handled and whether responses inadvertently reflect sensitive values. While the scanner does not inspect internal memory, it can identify risky patterns like missing input validation, excessive data exposure in responses, and missing controls around authentication headers, which correlate with insecure handling of uninitialized memory.

To mitigate uninitialized memory risks with Basic Auth in Fiber, ensure credentials are treated as sensitive byte data and cleared after use. Avoid relying on string conversions that may retain copies in memory, and prefer explicit byte handling with zeroing when possible. Validate and sanitize all inputs, and ensure responses never reflect raw credentials.

Use c.GetReqHeaders() to read the header as bytes, manually decode Base64, and overwrite buffers after processing:

app.Get('/api/secure', func(c *fiber.Ctx) error {
    auth := c.Get(fiber.HeaderAuthorization)
    if len(auth) < 7 || auth[:6] != "Basic " {
        return c.Status(fiber.StatusUnauthorized).SendString('Unauthorized')
    }
    encoded := auth[6:]
    decoded, err := base64.StdEncoding.DecodeString(string(encoded))
    if err != nil {
        return c.Status(fiber.StatusBadRequest).SendString('Invalid authorization header')
    }
    defer func(b []byte) { 
        for i := range b { 
            b[i] = 0 
        }
    }(decoded)

    parts := bytes.SplitN(decoded, []byte(":"), 2)
    if len(parts) != 2 {
        return c.Status(fiber.StatusBadRequest).SendString('Invalid credentials format')
    }
    user, pass := parts[0], parts[1]
    // Immediately validate user/pass (e.g., against a secure store)
    // Ensure pass is not retained or logged
    if !isValidUser(user, pass) {
        return c.Status(fiber.StatusUnauthorized).SendString('Unauthorized')
    }
    // Zero pass after use
    for i := range pass { pass[i] = 0 }
    return c.JSON(fiber.Map{"user": string(user)})
})

This approach reads the raw header, decodes Base64 into a byte slice, and explicitly zeroes the password buffer after validation. It avoids relying on c.BasicAuth()’s internal string allocations that may leave copies in memory. Always sanitize the username and password before any logging or external usage, and ensure error messages do not include raw credential values.

Additional measures include enforcing HTTPS to prevent credentials from traversing the network in clear text, setting short timeouts for authentication endpoints, and reviewing dependency behavior to ensure libraries do not retain references to credential buffers. MiddleBrick’s checks for authentication weaknesses, input validation, and data exposure help surface configurations that may leave credentials vulnerable through uninitialized memory or other side channels.