Open Redirect in Buffalo with Jwt Tokens

An open redirect in a Buffalo application becomes more risky when JWT tokens are involved because token handling flows can be abused to redirect authenticated users without their knowledge. In Buffalo, applications often parse a JWT from an Authorization header or a query parameter, validate it, and then use claims such as next or redirect_to to determine where to send the user after login or logout. If the redirect target is taken directly from user-controlled input and is not strictly validated against an allowlist, an attacker can supply a malicious URL, and the application will issue a 3xx response that includes the JWT in the Location header or in a subsequent request made by the browser.

Consider a typical post-login flow: after verifying credentials, Buffalo checks a JWT for session information and then reads a query parameter like redirect_to. If the parameter is used as-is with a relative or absolute URL without domain validation, an attacker can craft a link such as https://api.example.com/login?redirect_to=https://evil.com. When the victim clicks the link, logs in successfully, and the server responds with HTTP/1.1 303 See Other and Location: https://evil.com, the browser follows the redirect. Although the JWT may be stored in an HttpOnly cookie or returned in the response body, the mere redirection to a malicious site can facilitate phishing, session fixation, or token leakage via referrer headers.

JWT-specific aspects exacerbate the issue. If the token contains a redirect_uri claim used during OAuth flows, and the server uses that claim to decide where to send the user after authorization, an attacker who can influence or forge the token can direct the user to a harmful endpoint. Even when tokens are validated, a server that does not enforce strict same-origin policies for redirects can treat a trusted-looking token as sufficient justification to redirect anywhere. This is especially dangerous when combined with unauthenticated endpoints that expose status codes or headers, because an attacker can probe the redirect behavior without needing valid credentials.

Real-world patterns mirror known OWASP API Top 10 and general web security risks around authentication flows and insecure redirects. For example, an attacker might leverage a path traversal or open redirect to move from an unauthenticated endpoint to a token-exposed route. Because Buffalo encourages clean URLs and straightforward routing, developers may inadvertently trust query parameters for navigation. Without explicit allowlisting and strict validation, the framework’s convenience features can be turned into a vector for token leakage or phishing.

To detect such issues using methodology aligned with middleBrick, scanners test unauthenticated and authenticated routes that accept redirect parameters, inspect response headers for open redirects, and verify whether JWT handling logic exposes tokens in Location headers or logs. The scanner correlates findings with frameworks like OWASP API Top 10 and checks whether token validation is consistently applied before any navigation decision.

Remediation focuses on validating redirect targets and ensuring JWT usage does not enable untrusted navigation. In Buffalo, you should never use raw user input for HTTP redirects. Instead, maintain an allowlist of trusted paths and resolve redirects safely using the redirects helper while preserving token integrity through secure cookie attributes and strict validation.

Example 1: Safe Redirect with Allowlist

package actions

import (
    "github.com/gobuffalo/buffalo"
    "net/url"
)

func LoginNext(c buffalo.Context) error {
    // Assume JWT is validated and user identity established
    next := c.Param("next")
    allowedPaths := map[string]bool{
        "/dashboard": true,
        "/profile":   true,
        "/settings":  true,
    }
    if next == "" || !allowedPaths[next] {
        next = "/dashboard" // default safe location
    }
    // Ensure no token leakage in Location header
    c.Response().Header().Del("Location")
    return c.Redirect(303, urls.JoinPath(next))
}

Example 2: JWT Claims Handling Without Redirect Abuse

package actions

import (
    "github.com/gobuffalo/buffalo"
    "github.com/golang-jwt/jwt/v5"
)

func ProcessToken(c buffalo.Context) error {
    auth := c.Request().Header.Get("Authorization")
    if auth == "" {
        return c.Render(401, r.JSON(&map[string]string{"error": "missing authorization"}))
    }
    tokenString := auth[len("Bearer "):]
    token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
        // validate signing method and key
        return []byte("your-secret"), nil
    })
    if err != nil || !token.Valid {
        return c.Render(401, r.JSON(&map[string]string{"error": "invalid token"}))
    }
    // Do not use token claims for redirect URLs directly
    // Instead, map claims to internal safe routes
    claims := token.Claims.(jwt.MapClaims)
    role, _ := claims["role"].(string)
    var safeRoute string
    switch role {
    case "admin":
        safeRoute = "/admin"
    case "user":
        safeRoute = "/user"
    default:
        safeRoute = "/home"
    }
    return c.Redirect(303, safeRoute)
}

Example 3: Secure Cookie and Referrer Policy

package actions

import (
    "github.com/gobuffalo/buffalo"
)

func SecureRedirect(c buffalo.Context) error {
    // Set JWT in HttpOnly, Secure cookie with SameSite
    opts := &buffalo.CookieOptions{
        HttpOnly:   true,
        Secure:     true,
        SameSite:   buffalo.SameSiteStrictMode,
        MaxAge:     3600,
    }
    c.SetCookie("auth_token", "jwt-value", opts)
    // Use a relative safe path; avoid Location header manipulation
    return c.Redirect(303, "/dashboard")
}

Example 4: Validate Origin for State-Changing Redirects

package actions

import (
    "github.com/gobuffalo/buffalo"
    "net/http"
)

func Logout(c buffalo.Context) error {
    referer := c.Request().Header.Get("Referer")
    if referer != "" {
        u, err := url.Parse(referer)
        if err != nil || u.Host != c.Request().Host {
            // Invalid referrer, do not redirect to external origin
            referer = ""
        }
    }
    // Clear token cookie
    c.SetCookie("auth_token", "", &buffalo.CookieOptions{
        HttpOnly: true,
        Secure:   true,
        MaxAge:   -1,
    })
    if referer != "" {
        return c.Redirect(303, referer)
    }
    return c.Redirect(303, "/")
}