Jwt None Algorithm in Buffalo

The "none" algorithm in JWT processing is a known weakness that allows attackers to bypass authentication by submitting a token with an empty algorithm header. In Buffalo, this manifests when applications use the standard github.com/coreos/go-oidc or github.com/gorilla/securecookie libraries without explicit algorithm validation, or when custom JWT middleware is written without enforcing alg: "RS256" or similar. Buffalo applications often place JWT validation in route handlers or middleware, and if the code does not inspect token.Header.Algorithm, an attacker can send a token like header={alg: "none", typ: "JWT"} followed by an empty signature, which many decoders accept as valid. This leads to unauthenticated access to protected routes, including those behind @auth annotations or session middleware.

Specific Buffalo code paths where this appears include custom AuthMiddleware implementations that rely on third‑party JWT libraries without algorithm enforcement. For example, a Buffalo controller may call jwt.Decode(tokenString, &payload) without checking token.Header.Alg. If the library defaults to "none", the payload is accepted even when Signature is missing. Because Buffalo does not enforce algorithm constraints at the framework level, developers must manually reject tokens with alg: "none" or empty algorithm fields. Real‑world attacks have exploited this in Buffalo‑based SaaS platforms to gain admin access to APIs that expose inventory data or user profiles.

Detection requires scanning the API endpoint for JWT validation logic and confirming that the algorithm check is explicit. middleBrick can identify this by probing the unauthenticated attack surface and flagging responses where the server returns a successful authentication status without requiring a valid signature. The scanner maps the finding to the OWASP API Top 10 category Broken Object Level Authorization and assigns a severity based on the potential impact of unauthorized access.

Remediation must be performed in the application code, not by the scanner. Developers should enforce a strong algorithm such as RS256 or ES256 and reject any token that does not match the expected algorithm. For example, in a Buffalo middleware, you can add a check:

  if token.Header.Algorithm != "RS256" {
    http.Error(w, "invalid algorithm", http.StatusUnauthorized)
    return
  }

Another remediation step is to explicitly verify the signature when using a public key. In Buffalo, you can configure the JWT decoder to require a key:

  verifier := &jwt.Verifier{Key: kid.KeyFunc(apiKeyFunc)}
  _, err := jwt.Parse(tokenString, verifier)
  if err != nil {
    http.Error(w, "invalid token", http.StatusUnauthorized)
    return
  }

When middleBrick scans a Buffalo API, it performs a black‑box test by sending a JWT with alg: none and an empty signature. If the server authenticates the request, middleBrick logs this as a critical issue and returns a detailed finding, including the exact request payload, the endpoint URL, and a remediation guide that references the code snippets above. This scanning capability is part of the continuous monitoring offered in the Pro tier, allowing teams to detect regressions before they reach production.

JWT None Algorithm vulnerabilities in Buffalo applications can lead to unauthorized access if the middleware does not enforce a strong signing algorithm. middleBrick can detect this issue through black‑box scanning, providing actionable findings and remediation examples. The Pro plan includes continuous monitoring and CI/CD integration to ensure that such vulnerabilities are caught early in the development lifecycle.