angular/angular-cli · error · Error

Header "x-forwarded-proto" must be either "http" or "https".

Error message

Header "x-forwarded-proto" must be either "http" or "https".

What it means

Angular SSR validates the trusted `x-forwarded-proto` header against `/^https?$/i` (case-insensitive, first value only). Values like `https, http`, `wss`, or empty strings fail. This ensures the scheme used to rebuild absolute URLs in SSR is a safe http/https value.

Source

Thrown at packages/angular/ssr/src/utils/validation.ts:220

  const forwarded = headers.get('forwarded');
  if (forwarded) {
    const forwardedParams = parseForwardedHeader(forwarded);
    if (forwardedParams.host && !disableHostCheck) {
      verifyHostAllowed('Forwarded "host"', forwardedParams.host, allowedHosts);
    }
    if (forwardedParams.proto && !VALID_PROTO_REGEX.test(forwardedParams.proto)) {
      throw new Error('Header "forwarded" proto parameter must be either "http" or "https".');
    }
  }

  const xForwardedPort = getFirstHeaderValue(headers.get('x-forwarded-port'));
  if (xForwardedPort && !VALID_PORT_REGEX.test(xForwardedPort)) {
    throw new Error('Header "x-forwarded-port" must be a numeric value.');
  }

  const xForwardedProto = getFirstHeaderValue(headers.get('x-forwarded-proto'));
  if (xForwardedProto && !VALID_PROTO_REGEX.test(xForwardedProto)) {
    throw new Error('Header "x-forwarded-proto" must be either "http" or "https".');
  }

  const xForwardedPrefix = getFirstHeaderValue(headers.get('x-forwarded-prefix'));
  if (xForwardedPrefix && !VALID_PREFIX_REGEX.test(xForwardedPrefix)) {
    throw new Error(
      'Header "x-forwarded-prefix" is invalid. It must start with a "/" and contain ' +
        'only alphanumeric characters, hyphens, and underscores, separated by single slashes.',
    );
  }
}

/**
 * Checks if a specific proxy header is allowed.
 *
 * @param headerName - The name of the proxy header to check.
 * @param trustProxyHeaders - A set of allowed proxy headers.
 * @returns `true` if the header is allowed, `false` otherwise.
 */

View on GitHub (pinned to bb72145f9a)

Solutions

1. Configure the outermost proxy to overwrite x-forwarded-proto with exactly `http` or `https`.
2. Ensure only one proxy layer sets the header instead of appending.
3. Remove `x-forwarded-proto` from `trustProxyHeaders` if unused.
4. Fix load balancer rules (e.g. AWS ALB listeners) that inject non-standard values.

Example fix

// before
proxy_set_header X-Forwarded-Proto "$scheme, https";
// after
proxy_set_header X-Forwarded-Proto "$scheme";

const proto = request.headers.get('x-forwarded-proto')?.split(',')[0].trim();
if (proto && !/^(http|https)$/i.test(proto)) throw new Error(`Invalid x-forwarded-proto: ${proto}`);

try {
  validateHeaders(headers, allowedHosts, disableHostCheck);
} catch (e) {
  if ((e as Error).message.includes('x-forwarded-proto')) {
    return res.status(400).end('Invalid proto header');
  }
  throw e;
}

When it happens

Trigger: A request with a trusted `x-forwarded-proto` header whose first value is not `http` or `https` — e.g. `HTTP/2, https`, `wss`, or a comma-joined list where the first entry is invalid.

Common situations: CDNs/load balancers appending protocol lists; WebSocket terminators emitting `wss`; double proxying where the header accumulates values; stale proxies emitting `HTTP/1.1`.

Related errors

• Header "x-forwarded-port" must be a numeric value.
• Header "x-forwarded-prefix" is invalid. It must start with a
• Header "${headerName}" with value "${headerValue}" is not al
• Header "forwarded" proto parameter must be either "http" or
• "${TRUST_ALL_PROXY_HEADERS}" is not allowed as a value for t

AI-assisted analysis of angular/angular-cli@bb72145f9a (2026-08-30). Data as JSON: /api/errors/21e8cf1e37a9d4d7. Report an issue: GitHub.