projectdiscovery/nuclei · error

invalid host or port

Error message

invalid host or port

What it means

Thrown by the nuclei vnc JavaScript library's connect() when host is an empty string or port is <= 0 — the pre-flight check before any network policy lookup or dialing happens. It exists so callers fail fast on obviously invalid arguments instead of producing confusing dial errors from net.JoinHostPort or the fastdialer.

Source

Thrown at pkg/js/libs/vnc/vnc.go:59

// Connect connects to VNC server using given password.
// If connection and authentication is successful, it returns true.
// If connection or authentication is unsuccessful, it returns false and error.
// The connection is closed after the function returns.
// @example
// ```javascript
// const vnc = require('nuclei/vnc');
// const client = new vnc.VNCClient();
// const connected = client.Connect('acme.com', 5900, 'password');
// ```
func (c *VNCClient) Connect(ctx context.Context, host string, port int, password string) (bool, error) {
	executionId := ctx.Value("executionId").(string)
	return connect(ctx, executionId, host, port, password)
}

// connect attempts to authenticate with a VNC server using the given password
func connect(ctx context.Context, executionId string, host string, port int, password string) (bool, error) {
	if host == "" || port <= 0 {
		return false, fmt.Errorf("invalid host or port")
	}
	if !protocolstate.IsHostAllowed(executionId, host) {
		// host is not valid according to network policy
		return false, protocolstate.ErrHostDenied.Msgf(host)
	}

	dialer := protocolstate.GetDialersWithId(executionId)
	if dialer == nil {
		return false, fmt.Errorf("dialers not initialized for %s", executionId)
	}

	conn, err := dialer.Fastdialer.Dial(ctx, "tcp", net.JoinHostPort(host, strconv.Itoa(port)))
	if err != nil {
		return false, err
	}
	defer func() {
		_ = conn.Close()
	}()

View on GitHub (pinned to 265b3a3dec)

Solutions

1. Validate host is a non-empty string and port is a positive integer before calling Connect
2. Default the port to 5900 when your template leaves it dynamic
3. Log/skip the target when the connection parameters cannot be resolved

Example fix

// before
const ok = client.Connect(target, parsedPort, password); // parsedPort may be NaN

// after
const port = Number.isInteger(parsedPort) && parsedPort > 0 ? parsedPort : 5900;
if (target) {
  const ok = client.Connect(target, port, password);
}

function isValidVncTarget(host, port) { return typeof host === 'string' && host.length > 0 && Number.isInteger(port) && port > 0 && port < 65536; }
if (isValidVncTarget(host, port)) { client.Connect(host, port, password); }

function isValidVncTarget(host, port) { return typeof host === 'string' && host.length > 0 && Number.isInteger(port) && port > 0; }

try { client.Connect(host, port, password) } catch (e) { if (String(e) === 'invalid host or port') { /* fix inputs */ } else { throw e; } }

When it happens

Trigger: Calling client.Connect('', 5900, 'pass') or client.Connect('host', 0, 'pass'); passing a port parsed from a string with parseInt that returned NaN/0; host variables left empty because an extractor or template variable did not populate.

Common situations: Templates building host/port from dynamic variables that can be empty; JS type coercion surprises (port passed as string or undefined arithmetic); reused boilerplate where the port constant was removed.

Related errors

• file path cannot be empty
• invalid number of recipients: required 1, got %d
• parse target: %w
• invalid host or port
• invalid host or port

AI-assisted analysis of projectdiscovery/nuclei@265b3a3dec (2026-08-15). Data as JSON: /api/errors/5cf4fa7855fe8eb1. Report an issue: GitHub.