shadow1ng/fscan · error

%s [socks5_invalid_request]

Error message

%s [socks5_invalid_request]

What it means

Guard in handleSocks5Request rejecting a SOCKS5 request header that is not well-formed: the version byte (header[0]) is not 0x05 or the reserved byte (header[2]) is not 0x00. It fires when a client connected to the local SOCKS5 proxy port sends a malformed or non-SOCKS5 request, before any command or address parsing.

Source

Thrown at plugins/local/socks5proxy.go:197

	// 发送握手响应（无认证）
	response := []byte{0x05, 0x00} // 版本5，无认证
	if _, err := conn.Write(response); err != nil {
		return fmt.Errorf("%s: %w", i18n.GetText("socks5_handshake_write_failed"), err)
	}

	return nil
}

// handleSocks5Request 处理SOCKS5连接请求
func (p *Socks5ProxyPlugin) handleSocks5Request(clientConn net.Conn, session *common.ScanSession) (net.Conn, int, error) {
	header := make([]byte, 4)
	if _, err := io.ReadFull(clientConn, header); err != nil {
		return nil, 0, fmt.Errorf("%s: %w", i18n.GetText("socks5_request_read_failed"), err)
	}

	if header[0] != 0x05 || header[2] != 0x00 {
		return nil, 0, fmt.Errorf("%s", i18n.GetText("socks5_invalid_request"))
	}

	cmd := header[1]
	if cmd != 0x01 { // 只支持CONNECT命令
		// 发送不支持的命令响应
		response := []byte{0x05, 0x07, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}
		_, _ = clientConn.Write(response)
		return nil, 0, fmt.Errorf(i18n.GetText("socks5_unsupported_command")+": %d", cmd)
	}

	// 解析目标地址
	addrType := header[3]
	var targetHost string
	var targetPort int

	switch addrType {
	case 0x01: // IPv4
		addr := make([]byte, 6)

View on GitHub (pinned to 95cc12e753)

Solutions

1. Use a SOCKS5-compliant client/proxy consumer
2. Verify the client library's request framing against RFC 1928
3. Reject and close the connection; log the peer for diagnosis

When it happens

Trigger: Thrown at plugins/local/socks5proxy.go:197 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of shadow1ng/fscan@95cc12e753 (2026-09-06). Data as JSON: /api/errors/a35e57e44f78305b. Report an issue: GitHub.