There are hundreds of HTTP or FTP error codes, some more serious than others. You’ve probably encountered HTTP error 533 if you have ever tried to modify web servers or FTP requests. However, it is rare.

What does HTTP error 533 actually mean?

Know how can you remove it from your computer if it appears?

An HTTP error code 533 can occur when a security command sent on the fly is not able to be implemented due to the server configuration. This is a rare error that can be difficult to diagnose, regardless of how long you have been working with a server or web technology such as FTP.

This guide will explain in detail the 533 error message. It will also discuss how to fix it if it appears on your command output or server logs.

What is “error code 533”?

When a command is issued to modify a command channel that has security restrictions, the 533 error code will be generated. It sounds confusing, but the keywords are security rules and command channel. When an FTP server issue a command, or set of commands, 533 errors are part of another set.

An HTTP/FTP error 533 indicates that there is something wrong with the server configuration or command. As intended, the error means that the server refuses to accept the command. It will throw an error every time unless the command or security configuration are changed.

What is Error 533?

There are two to three possible causes of HTTP error 533 depending on the FTP command being used and the server security configuration.

When issuing CCC FTP Commands

If you use the CCC command (Clear Command Channel), to authorize NAT functions on routers and have the secured command channel revert back to plain text, you will get a 533 error. This can only be done if the client is behind a NAT router and is able to access port 21.

Clear Command Channel requests will, as expected, require modification of channel command protection levels (reverting back to plain text). In certain situations, the 533 error would be thrown.

When issuing SSCN FTP commands

Requests or commands for SSCN FTP may sometimes trigger the rare 533 response if security configurations disagree with the command. To specify secure file transfers between FXP servers, the SSN command (Set Secure Client negotiation Command in full) can be used. FXP (File Exchange Protocol in Full) is a data transfer protocol that allows files to be sent between remote servers.

SSCN commands will, naturally, try to modify channel command protection levels, triggering the 533 error.

Filename Restrictions

A common issue is that FTP server filename restrictions can cause an HTTP error 533. Cute Ftp, for example, is known to produce the 533 error message when filename violation occurs. This error is caused by filename violations that are not within the security protocols of the remote server to which it is being uploaded.

How to Fix Error 533 Easily?

To get rid of the 533 error, you can modify server security configuration to allow the commands that you wish to issue. This involves going to the config file of the remote server and looking for the security channel command configuration.

You could also avoid inter-server file transfers protocols. You should instead choose more secure and proven methods like SFTP (SSL file transfer protocol), FTPS, File transfer protocol over SSL (File transfer protocol via SSL) and MFP if available. FXP was originally designed to transfer files in an unencrypted format. SSCN is a workaround to ensure some security.

If FTP fails to transfer files, the third option is not possible. This error can be caused by filenames with illegal characters. These methods will help you fix the problem.

Filenames are too long. A shorter filename could fix the problem.

Do any file names in FTP upload queue contain special characters? These characters and spaces can sometimes cause 533 errors during upload. The error might be fixed by changing the filename to contain alphanumeric characters.

Is your file path too long? Sometimes, a file path might be nested in multiple folders within the FTP upload queue. You might get 533 errors if you change the file path.


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