Http Request Smuggling in Buffalo with Jwt Tokens

Http Request Smuggling is an attack that exploits discrepancies in how request boundaries are parsed, commonly involving conflicting Content-Length and Transfer-Encoding headers. When JWT tokens are used for authentication in a Buffalo application, the interaction between the smuggling vector and the token handling logic can expose or amplify security risks.

In Buffalo, JWTs are typically validated on each request before routing to handlers. If the framework or underlying server configuration does not enforce strict header parsing, an attacker can craft a request that is interpreted differently by a frontend proxy versus the application server. For example, a request with both Content-Length: 0 and Transfer-Encoding: chunked may be processed correctly by the proxy but misinterpreted by the backend, causing the request body to be improperly separated. This can lead to request splitting, where one request is treated as two, or request tampering, where an authenticated request with a valid JWT is split into an authenticated and an unauthenticated request.

Because JWTs are often passed in the Authorization header, the token may be associated with the first request while the second, unauthenticated request is allowed to proceed. This can bypass intended access controls, especially if middleware that validates JWTs does not account for request boundary ambiguity. Additionally, because Buffalo applications often compose handlers and middleware, a misconfigured or lenient parser can allow a smuggled request to reach sensitive endpoints that would otherwise be protected by JWT validation.

The risk is further influenced by how middleware is ordered. If JWT validation occurs after body parsing and the parser is tricked by a smuggled body, the token may not be correctly associated with the intended logical request. This misalignment can lead to unauthorized access or data leakage when the framework assumes the context of the request is consistent across the proxy boundary.

Remediation focuses on strict header processing, consistent middleware ordering, and explicit JWT validation practices in Buffalo applications.

• Enforce a single header parsing mode: configure your frontend proxy and application server to either use Content-Length or Transfer-Encoding, never both. For Go-based Buffalo apps, ensure the underlying HTTP server settings are aligned with this policy.
• Validate JWTs before any body processing in the middleware chain. This ensures that the request context and token are established before parsing the body, reducing the impact of any boundary ambiguity.
• Use explicit, secure token parsing and verification. The following example demonstrates JWT validation in a Buffalo middleware using github.com/golang-jwt/jwt/v5:

// middleware/jwt_auth.go
package middleware

import (
    "net/http"
    "strings"

    "github.com/golang-jwt/jwt/v5"
)

func JWTValidator(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        authHeader := r.Header.Get("Authorization")
        if authHeader == "" {
            http.Error(w, "Authorization header required", http.StatusUnauthorized)
            return
        }
        parts := strings.Split(authHeader, " ")
        if len(parts) != 2 || parts[0] != "Bearer" {
            http.Error(w, "Invalid authorization format", http.StatusUnauthorized)
            return
        }
        tokenString := parts[1]
        token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
            if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
                return nil, &jwt.ErrSignatureInvalid
            }
            return []byte("your-secret-key"), nil
        })
        if err != nil || !token.Valid {
            http.Error(w, "Invalid token", http.StatusUnauthorized)
            return
        }
        next.ServeHTTP(w, r)
    })
}

• Apply Content-Length validation for known-safe ranges and reject requests with ambiguous or missing length when handling authenticated endpoints.
• Leverage the middleBrick dashboard and scans to detect inconsistencies in how your API endpoints handle headers and tokens. You can track scans over time using the dashboard, and if you need more rigorous enforcement in CI/CD, the Pro plan includes the GitHub Action to fail builds if risk scores drop below your chosen threshold.