Open Redirect in Echo Go with Bearer Tokens

An open redirect in an Echo Go service becomes more risky when Bearer tokens are involved because clients often include the token in query parameters or fragments during the redirect flow. If the redirect target is derived from user-controlled input without strict validation, an attacker can supply a malicious URL such as https://api.example.com/callback?token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9 and trick the application into redirecting the authenticated user to that URL while the token remains in the request context or is inadvertently reflected in the Location header.

In Echo Go, a common vulnerable pattern is to read a next or return_to query parameter and use redirect.SeeOther(next) without verifying that the target belongs to a trusted set of domains. Because Bearer tokens are frequently passed via Authorization headers, developers may assume they are safe from redirect-based leakage. However, if the token is also stored in a query string for analytics or session continuity, and that query string is concatenated into the redirect location, the token can be exposed to the external site. This can lead to token replay if the token is leaked in browser history, Referer headers, or logs.

For example, consider an Echo Go callback handler that processes an OAuth flow:

package main

import (
    "net/http"
    "github.com/labstack/echo/v4"
)

func callback(c echo.Context) error {
    token := c.QueryParam("token")
    next := c.QueryParam("next")
    // Vulnerable: next is used without validation
    return c.Redirect(http.StatusSeeOther, next)
}

An attacker can set next to a domain they control, causing the user’s browser to navigate away with the token in the URL. Even if the token is intended for backend use only, combining it with an unchecked redirect creates a conduit for exfiltration. This pattern intersects with common web vulnerabilities such as improper neutralization of authentication elements and lack of strict allowlists for redirects, which are highlighted in the OWASP API Top 10 and mapped to findings in middleBrick scans.

middleBrick detects such issues by analyzing the unauthenticated attack surface and flagging endpoints where redirect locations are influenced by external input. When scans include Bearer token contexts, the tool can identify whether tokens are reflected in headers or responses that could accompany a redirect, providing prioritized findings with severity and remediation guidance.

To remediate open redirect risks in Echo Go when Bearer tokens are present, enforce strict allowlisting of redirect targets and avoid reflecting tokens in URLs. Never concatenate untrusted input into a Location header. Instead, validate the target against a predefined list of trusted hosts or paths.

Below is a secure implementation example that uses a whitelist approach and preserves authentication without leaking tokens in redirects:

package main

import (
    "net/url"
    "strings"

    "github.com/labstack/echo/v4"
)

var allowedHosts = map[string]bool{
    "app.example.com": true,
    "dashboard.example.com": true,
}

func safeRedirect(c echo.Context) error {
    next := c.QueryParam("next")
    if next == "" {
        next = "/dashboard"
    }

    parsed, err := url.Parse(next)
    if err != nil || parsed.Scheme == "" || parsed.Host == "" {
        // Invalid URL, fallback to default
        return c.Redirect(http.StatusSeeOther, "/dashboard")
    }

    if !allowedHosts[parsed.Host] {
        // Host not allowed, reject redirect
        return c.Redirect(http.StatusSeeOther, "/dashboard")
    }

    // Ensure token is not passed via query; rely on secure session or header context
    // For example, use a session cookie with HttpOnly and SameSite attributes
    return c.Redirect(http.StatusSeeOther, parsed.String())
}

Additionally, when issuing Bearer tokens, keep them in HTTP-only cookies or in Authorization headers only, and avoid adding them to query strings. If you must include token context for single-page applications, use short-lived tokens and ensure that redirect endpoints do not log or expose the full URL with tokens. The Echo middleware below demonstrates how to strip sensitive query parameters before logging or redirecting:

func sanitizeMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        // Remove token from query to prevent leakage in logs and redirects
        query := c.Request().URL.Query()
        query.Del("token")
        c.Request().URL.RawQuery = query.Encode()
        return next(c)
    }
}

By combining input validation for redirect targets with disciplined handling of Bearer tokens, you reduce the attack surface for open redirect vulnerabilities. middleBrick’s scans can verify that such controls are in place by checking endpoint behavior and flagging any redirects that do not enforce strict host allowlists.