如何修复 OpenSSL SSLERRORSYSCALL：连接建立失败 – wiki词典

作者： /

This error, OpenSSL SSL_SYSCALL_ERROR: Connection established failed, is a common and often frustrating issue encountered when applications attempt to establish an SSL/TLS connection. It indicates a failure at a low level during the connection process, often before the SSL/TLS handshake can even properly begin. This article will detail the potential causes and provide comprehensive troubleshooting steps to resolve it.

Understanding SSL_SYSCALL_ERROR and “Connection established failed”

SSL_SYSCALL_ERROR in OpenSSL means that a system call (like read, write, or connect) failed. When accompanied by “Connection established failed,” it specifically points to a problem during the initial phase of setting up the network connection at the TCP/IP level, or a very early failure in the SSL/TLS layer due to an underlying network issue.

Unlike SSL_ERROR_WANT_READ or SSL_ERROR_SSL, which indicate issues during the SSL/TLS handshake itself, SSL_SYSCALL_ERROR suggests that the operating system’s network functions failed to complete the connection to the remote server or encountered an unexpected state.

Common Causes

Here are the most frequent reasons you might encounter this error:

  1. Network Connectivity Issues:

    • Server Offline/Incorrect Address: The target server is not running, is not listening on the specified port, or the IP address/hostname is incorrect.
    • Firewall Restrictions: A firewall (client-side, server-side, or network intermediary) is blocking the connection on the specified port.
    • Routing Problems: Network routing issues prevent the client from reaching the server.
    • Proxy Server Interference: If a proxy is in use, it might be misconfigured or blocking the SSL/TLS traffic.

  2. SSL/TLS Version or Cipher Mismatch:

    • While SSL_SYSCALL_ERROR usually points to lower-level issues, an extreme mismatch in supported SSL/TLS versions or cipher suites between the client and server can sometimes manifest in this way if the initial “Client Hello” cannot even be sent or understood.

  3. Certificate Issues (Less Common for SYSCALL, but possible):

    • Though more commonly associated with SSL_ERROR_SSL, an invalid or expired server certificate, or one that cannot be trusted by the client, could potentially halt the connection process very early if certain strict client configurations are in place.

  4. DNS Resolution Problems:

    • If the hostname cannot be resolved to an IP address, the connection attempt will fail.

  5. System Resources/Limits:

    • On rare occasions, too many open file descriptors or other system resource limitations can prevent new connections from being established.

  6. Antivirus/Security Software:

    • Aggressive antivirus, anti-malware, or “man-in-the-middle” SSL inspection software on the client or network can intercept and break the connection.

Troubleshooting Steps

Follow these steps systematically to diagnose and fix the issue:

1. Verify Basic Network Connectivity

  • Ping the Server:
    bash
    ping <server_hostname_or_ip>
    If ping fails, there’s a fundamental network reachability problem.

  • Test Port Reachability:

    • Using telnet (Windows/Linux):
      bash
      telnet <server_hostname_or_ip> <port>
      A successful connection usually shows a blank screen or a welcome banner. A “Connection refused” or “Connect failed” message indicates the server isn’t listening or a firewall is blocking.
    • Using nc (netcat – Linux/macOS):
      bash
      nc -zv <server_hostname_or_ip> <port>
      (-z for zero-I/O mode, -v for verbose output).

  • Check Server Status: Ensure the application providing the SSL/TLS service on the server is running and configured to listen on the correct IP address and port.

2. Examine Firewalls

  • Client-Side Firewall: Check your operating system’s firewall (Windows Defender Firewall, ufw on Linux, macOS Firewall) to ensure outgoing connections on the target port are allowed.
  • Server-Side Firewall: Verify that the server’s firewall (e.g., iptables, firewalld, cloud security groups) permits incoming connections on the SSL/TLS port (typically 443).
  • Network Firewalls: If you are in a corporate network, contact your IT department to check if any network-level firewalls are blocking the traffic.

3. Inspect Proxy Settings

  • If your application or system uses a proxy server, ensure it’s correctly configured and not interfering with SSL/TLS connections.
  • Try bypassing the proxy temporarily if possible, or test the connection from a network without a proxy.
  • Check if your application is correctly using the proxy’s certificate authority (CA) if it’s an SSL-inspecting proxy.

4. Test with openssl s_client (Advanced Diagnosis)

This powerful command-line tool can simulate a client connection and provide detailed SSL/TLS handshake information.

bash
openssl s_client -connect <server_hostname_or_ip>:<port> -servername <server_hostname>
* Replace <server_hostname_or_ip> and <port> with your target.
* -servername <server_hostname> is crucial for SNI (Server Name Indication), especially if the server hosts multiple domains.

What to look for in the openssl s_client output:
* If it hangs or fails immediately with “Connection refused,” it points to a network or server availability issue (firewall, server down).
* If it connects but then shows errors, the output will often reveal details about certificate issues, SSL/TLS version mismatches, or cipher problems.

5. Check DNS Resolution

  • Client-Side:
    bash
    nslookup <server_hostname>
    Ensure the hostname resolves to the correct IP address. If it doesn’t, check your DNS server settings or /etc/resolv.conf (Linux).
  • Server-Side: Ensure the server can be resolved correctly if it’s a multi-host setup.

6. Synchronize System Clocks

  • Significant clock skew (time difference) between the client and server can cause certificate validation failures, which might manifest as a connection error. Ensure both systems have their clocks synchronized (e.g., using NTP).

7. Review Application and Server Logs

  • Client Application Logs: If your application logs its SSL/TLS errors, examine them for more context. Increase logging verbosity if possible.
  • Server Logs: Check the logs of the SSL/TLS-enabled server (e.g., Apache, Nginx, application server logs) for any errors related to incoming connections or SSL/TLS handshakes at the time of the failure.

8. Consider Antivirus/Security Software

  • Temporarily disable any antivirus, anti-malware, or network inspection software on your client machine and re-test. If the connection succeeds, you’ve found the culprit. You’ll then need to configure your security software to allow the connection.

9. Update OpenSSL/System Libraries

  • Ensure that both your client and server operating systems and the OpenSSL libraries they use are up-to-date. Older versions might have bugs or lack support for modern TLS versions and cipher suites.

10. Code-Specific Considerations (if applicable)

  • Python (e.g., requests library):
    python
    import requests
    try:
    response = requests.get("https://your.server.com/api", verify=True)
    print(response.status_code)
    except requests.exceptions.SSLError as e:
    print(f"SSL Error: {e}")
    except requests.exceptions.ConnectionError as e:
    print(f"Connection Error: {e}")
    except Exception as e:
    print(f"Other Error: {e}")
    The verify parameter (default True) checks SSL certificates. If you are absolutely sure of the identity of the server (e.g., in a trusted internal network), you could temporarily set verify=False for testing (not recommended for production) to see if it’s a certificate validation issue.
  • Java:
    Java applications often throw SSLHandshakeException or IOException with nested SSLHandshakeException details. Ensure your Java Keystore (cacerts) contains the necessary root certificates for the server you are connecting to.
  • Node.js:
    Node.js might report DEPTH_ZERO_SELF_SIGNED_CERT or similar errors if certificates are not trusted. The rejectUnauthorized option in https.request can be set to false for testing (not recommended for production).

Conclusion

The OpenSSL SSL_SYSCALL_ERROR: Connection established failed error is primarily a low-level network or system issue rather than an SSL/TLS protocol error. By systematically checking network connectivity, firewall rules, proxy settings, DNS resolution, and server availability, you can usually pinpoint and resolve the underlying cause. Utilizing tools like ping, telnet/nc, and especially openssl s_client, will provide invaluable diagnostic information to guide you to a solution.

滚动至顶部