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Unable to connect to Serv-U SFTP or SSH after upgrading to the latest version from 15.5.0 or older.

This article describes the issue in which after the upgrade to Serv-U 15.5.1, some or all of the SFTP or SSH connections are suddenly not working.

First published date

5/30/2025 7:40 AM

Last published date

7/22/2026 6:05 PM

Overview

Starting with Serv-U 15.5.1, it has been announced that the SSH-RSA key algorithm will be deprecated and disabled, but a newer, more secure version can be enabled if needed.
Ref: Serv-U 15.5.1 release notes 
This change will affect all user who uses SSH-RSA as SFTP/SSH Host Key and Serv-U users who use private/public key authentication to connect to the SFTP server.

 

Product section

Serv-U Managed File Transfer & Serv-U FTP Server

Cause

For security reasons, SSH-RSA has been deprecated.

Resolution

  • Option 1:
    • Use a secure SSH/SFTP Key Type for SSH Host Key and user SSH Key Authentication, like DSA or ECDSA.
  • Option 2:
    • SolarWinds recognized the impact of this Security Upgrade so there is an option to still allow SSH-RSA to the Serv-U Environment.
      • Enable SSH-RSA in the Serv-U Management Console. 
        • Go to Global > Limit & Settings > Encryption or Serv-U Domain > Limit & Settings > Encryption
        • Scroll down and look for "SSH-RSA"
        • Uncheck to Disable and Check to Enable