Open Redirect in Buffalo with Bearer Tokens

An open redirect in a Buffalo application becomes particularly risky when combined with Bearer Token handling, because it can be used to strip tokens from legitimate requests and redirect users to attacker-controlled destinations. In Buffalo, a typical pattern for authenticated flows might validate a token and then decide where to send the user. If the redirect target is derived from user input (e.g., a next parameter) without strict allowlisting, an attacker can supply a malicious URL that causes the application to redirect after token validation, making the token appear to be used in a trusted context.

Consider a login or OAuth callback handler that reads a Bearer token from an Authorization header, validates it, and then redirects based on a query parameter like redirect_to. If the application does not enforce an allowlist of trusted origins, an attacker can craft a URL such as https://api.example.com/auth/callback?redirect_to=https://evil.com. After the token is verified, Buffalo can issue a 302 to the attacker’s site, and although the Bearer token itself may not be exposed in the redirect, the combination weakens the trust model: clients that rely on the redirect being to a known origin may send tokens alongside the request, inadvertently exposing them in logs or browser history if the redirect is to a data URL or a malicious site that captures further authentication flows.

From a scanning perspective, middleBrick tests this attack surface by probing endpoints that accept unauthenticated requests and checking whether redirects can be influenced via input parameters. It specifically flags cases where a 3xx response can be triggered with a user-supplied URL and where authentication mechanisms like Bearer tokens are present in the request or response flow. This is part of the BOLA/IDOR and Authentication checks, which look for logic flaws in how identity and navigation are handled. The LLM/AI Security checks also examine whether prompt injection or data exfiltration probes can manipulate redirect behavior, which is relevant when token handling logic is exposed through API endpoints that accept external input.

Real-world mappings include OWASP API Top 10:2023 A05:2023 Security Misconfiguration and A01:2023 Broken Access Control, as improper redirect configurations can bypass intended access boundaries. PCI-DSS and SOC2 controls also expect strict validation of return URLs and secure handling of authentication tokens. middleBrick’s OpenAPI/Swagger spec analysis helps identify such risks by correlating spec-defined security schemes (like bearerAuth) with runtime behavior, ensuring that documented authentication mechanisms are not undermined by unchecked redirect parameters.

To remediate open redirect vulnerabilities in Buffalo while using Bearer Tokens, you must enforce strict allowlisting for redirect targets and ensure token handling does not depend on client-supplied URLs. Below are concrete code examples that demonstrate safe patterns.

1. Validate redirect targets with an allowlist

Never use raw user input for redirects. Instead, compare the target against a predefined list of trusted origins.

// In a Buffalo action
func AuthCallback(c buffalo.Context) error {
    token := c.Request().Header.Get("Authorization")
    if token == "" {
        return c.Error(401, errors.New("missing bearer token"))
    }
    // Validate token (pseudo-validation)
    if !isValidBearerToken(token) {
        return c.Error(401, errors.New("invalid token"))
    }

    // Safe: use a hardcoded or config-based default
    redirectTo := "/dashboard"
    if raw := c.Params().Get("redirect_to"); raw != "" {
        allowed := map[string]bool{"/dashboard": true, "/profile": true, "/settings": true}
        if !allowed[raw] {
            return c.Error(400, errors.New("invalid redirect target"))
        }
        redirectTo = raw
    }

    c.Response().Header().Set("Authorization", "Bearer "+token)
    return c.Redirect(302, redirectTo)
}

2. Use absolute URL allowlisting with net/url

For more control, parse and validate the redirect URL to ensure it matches expected hosts and schemes.

import (
    "net/url"
)

func safeRedirect(c buffalo.Context) error {
    raw := c.Params().Get("next")
    if raw == "" {
        raw = "/home"
    }
    u, err := url.Parse(raw)
    if err != nil || u.Host == "" {
        return c.Error(400, errors.New("invalid URL"))
    }
    // Allowlist host
    allowedHost := "app.example.com"
    if u.Host != allowedHost || (u.Scheme != "https" && u.Scheme != "") {
        return c.Error(400, errors.New("redirect to disallowed host"))
    }
    http.Redirect(c.Response(), c.Request(), u.String(), http.StatusFound)
    return nil
}

3. Avoid storing tokens in query parameters

Ensure Bearer tokens are only transmitted via headers and are never appended to redirect URLs. If you must pass state, use opaque identifiers and server-side mapping instead of raw tokens.

// Bad: token in query
// http.Redirect(w, r, "/callback?token=abc123", http.StatusFound)

// Good: keep token in header, use session or server-side state
sessionToken := generateSessionToken()
sessionStore[sessionToken] = "user-id"
http.Redirect(w, r, "/callback?state="+sessionToken, http.StatusFound)

These patterns align with the remediation guidance provided by middleBrick findings. The scanner can detect whether your endpoints are susceptible to open redirect by testing with manipulated parameters and will report findings with severity and specific remediation steps. For ongoing protection, consider the Pro plan, which includes continuous monitoring and configurable scanning schedules so that new redirect logic is automatically evaluated for risk.