Open Redirect in Echo Go with Basic Auth

An open redirect occurs when an application redirects a user to an arbitrary URL without proper validation of the destination. In Echo Go, this typically arises when a redirect handler uses an untrusted parameter to construct the Location header. When Basic Authentication is used, the risk pattern changes because authentication state and redirect logic can interact in ways that expose internal endpoints or bypass intended access controls.

Consider a handler that first performs Basic Auth validation and then conditionally redirects based on a query parameter such as next. If the next value is used directly without validation, an authenticated user (or an unauthenticated user if the auth check is misapplied) can be redirected to a malicious site. This becomes more dangerous when the Basic Auth realm exposes internal services (e.g., admin panels) and the redirect parameter is not restricted to same-origin paths.

For example, an attacker might craft a URL like /login?next=https://evil.com/steal. If the server redirects without validating that the target is local, the user’s browser leaves the trusted domain. In a Basic Auth context, if the redirect occurs after a successful but minimal auth check (for instance, checking username/password but not the requested path), the user may be moved to a phishing page while still appearing authenticated. The combination of Basic Auth and open redirect can therefore facilitate credential harvesting, session fixation, or unauthorized navigation to internal resources that should not be externally reachable.

Echo Go applications may also expose open redirects through misuse of the http.Redirect helper when combined with route parameters or headers like Referer. If the redirect target is derived from request headers that can be influenced by an attacker (e.g., Referer or a custom header), and Basic Auth is applied inconsistently across the redirect flow, the effective security boundary is weakened.

From an LLM/AI Security perspective, this specific combination can be probed by active prompt injection tests that simulate authenticated sessions and attempt to redirect the flow. middleBrick’s LLM security checks include active prompt injection testing (five sequential probes: system prompt extraction, instruction override, DAN jailbreak, data exfiltration, cost exploitation) and output scanning for PII, API keys, and executable code. These checks help surface logic flaws like open redirects in authenticated flows that might otherwise be overlooked in manual testing.

To detect such issues, middleBrick scans the unauthenticated attack surface and, when an OpenAPI/Swagger spec is available, cross-references spec definitions with runtime findings. This means that even without credentials, patterns indicative of open redirects in paths that are expected to be protected (e.g., admin routes) can be flagged, with remediation guidance included in the prioritized findings.

Remediation focuses on validating redirect targets and ensuring that Basic Auth is applied consistently and correctly. Never use untrusted input directly in a redirect. Instead, restrict redirects to same-origin paths or explicitly enumerated safe targets.

Example of a vulnerable pattern in Echo Go:

func vulnerableLogin(c echo.Context) error {
    username, password, ok := c.Request().BasicAuth()
    if !ok || !isValidUser(username, password) {
        return c.String(http.StatusUnauthorized, "Unauthorized")
    }
    next := c.QueryParam("next")
    if next != "" {
        return c.Redirect(http.StatusFound, next)
    }
    return c.String(http.StatusOK, "Welcome")
}

In this example, the next parameter is used directly in c.Redirect. An attacker can supply an external URL, causing the user to be redirected after successful Basic Auth validation.

Secure remediation involves validating the redirect target against a whitelist or ensuring it is a relative path:

Secure Echo Go handler with Basic Auth:

func secureLogin(c echo.Context) error {
    username, password, ok := c.Request().BasicAuth()
    if !ok || !isValidUser(username, password) {
        return c.String(http.StatusUnauthorized, "Unauthorized")
    }
    next := c.QueryParam("next")
    if next != "" {
        // Validate that next is a relative path and optionally restrict to known routes
        if !isSafeRedirect(next) {
            return c.String(http.StatusBadRequest, "Invalid redirect target")
        }
        return c.Redirect(http.StatusFound, next)
    }
    return c.String(http.StatusOK, "Welcome")
}

// isSafeRedirect allows only same-origin relative paths or a strict set of paths
func isSafeRedirect(target string) bool {
    // Reject URLs with a scheme or host
    if strings.Contains(target, "://") {
        return false
    }
    // Ensure it's a relative path
    if filepath.IsAbs(target) {
        return false
    }
    // Optionally restrict to known safe paths
    allowed := map[string]bool{
        "/dashboard": true,
        "/profile":   true,
        "/settings":  true,
    }
    if allowed[target] {
        return true
    }
    // Allow relative paths not containing ".." or leading slash
    return !strings.Contains(target, "..") && !strings.HasPrefix(target, "/")
}

Key points in the secure approach:

• Basic Auth credentials are validated before any redirect decision.
• The next parameter is checked by isSafeRedirect to ensure it is a relative path, does not contain a scheme or host, and is limited to a small set of allowed routes.
• If the redirect target cannot be validated, the server responds with a 400 Bad Request instead of redirecting, preventing open redirect abuse.

For broader protection, consider using a fixed mapping (e.g., a token or session-based return URL) instead of a free-form query parameter. This eliminates the risk of external redirection entirely while still supporting post-login navigation.