使用Python ftplib连接含未信任证书的FTPS服务器时出现OSError: [Errno 0] Error问题求助

I’ve run into this exact issue before—bypassing certificate verification for FTPS in Python’s ftplib requires a bit more than just using _create_unverified_context. Let’s break down the solution step by step.

The Root Cause #

Your original error stems from two key issues:

1. Even when using _create_unverified_context, the SSL context might still enforce hostname validation (since check_hostname defaults to True), causing handshake failures.
2. You likely didn’t switch the data connection to TLS mode after login—commands like dir() rely on this secure data channel, and skipping it leads to the OSError you’re seeing.

Working Solution #

Here’s the corrected code that properly disables certificate checks and ensures the data connection uses TLS:

import ftplib
import ssl

# Create a custom SSL context that skips all certificate validation
ctx = ssl.create_default_context()
ctx.check_hostname = False
ctx.verify_mode = ssl.CERT_NONE

# Initialize FTP_TLS with our custom context
ftp = ftplib.FTP_TLS(context=ctx)
ftp.connect("your-hostname", 21)  # Replace with your server's host and port
ftp.login("your-username", "your-password")

# Critical: Switch the data connection to TLS mode
ftp.prot_p()

# Now you can run dir() without certificate errors
ftp.dir()

Alternative Approach (Modifying Default Context) #

If you prefer not to create a separate context, you can modify the default context of the FTP_TLS instance directly:

import ftplib
import ssl

ftp = ftplib.FTP_TLS()
# Disable certificate verification on the default context
ftp.context.check_hostname = False
ftp.context.verify_mode = ssl.CERT_NONE

ftp.connect("your-hostname", 21)
ftp.login("your-username", "your-password")
ftp.prot_p()
ftp.dir()

Why Your Previous Attempts Failed #

• Using _create_unverified_context alone wasn’t enough because check_hostname remained enabled, triggering hostname validation even when certificate checks were turned off.
• Forgetting prot_p() meant the data connection (used for dir(), file transfers, etc.) wasn’t encrypted, leading the server to reject the unsecure connection during handshake.

Important Security Note #

Disabling certificate verification should only be done for trusted internal servers or testing environments—this bypasses critical security checks that protect against man-in-the-middle attacks.

内容的提问来源于stack exchange，提问作者trivelt