Because the two (client and server) are unable to negotiate a key exchange method, no connection is established.Ĭertain elements in the Diffie Hellman key exchange algorithm can have vulnerabilities. Unfortunately, FileZilla has stopped supporting this particular algorithm due to vulnerability issues. During the negotiation process of the SSH file transfer, some SFTP servers recommend the Diffie-Hellman-Group1-SHA1 for the key exchange. The problem lies in the SSH key exchange algorithm. Other SFTP client applications as well as SFTP servers acting as clients likewise generate similar error messages. The specific error message they get goes like this:Įrror: The first key-exchange algorithm supported by the server is diffie-hellman-group1-sha1, which is no longer secure. We often hear this complaint from admins whose users are trying to connect through later versions of FileZilla. FileZilla can't connect to your SFTP server If you're running a SFTP service, chances are you've already received connectivity-related complaints involving the diffie-hellman-group1-sha1 key exchange algorithm.

Filezilla sftp slow