Questo è un breve post su come disabilitare gli algoritmi HMAC basati su MD5 per ssh su Linux.
1. Assicurati di aver aggiornato il pacchetto openssh all'ultima versione disponibile.
2. Per modificare i cifrari/md5 in uso è necessario modificare il file sshd_config, puoi aggiungere Ciphers e MAC con le opzioni come da pagina man. Ad esempio:
# vi /etc/ssh/sshd_config Ciphers aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,arcfour MACs hmac-sha1,[email protected],hmac-ripemd160,hmac-sha2-256,hmac-sha2-512,[email protected]
Dalla pagina man di sshd_config:
# man sshd_config
Ciphers
Specifies the ciphers allowed for protocol version 2. Multiple ciphers must be comma-separated. The supported ciphers are
“3des-cbc”, “aes128-cbc”, “aes192-cbc”, “aes256-cbc”, “aes128-ctr”, “aes192-ctr”, “aes256-ctr”, “arcfour128”, “arcfour256”,
“arcfour”, “blowfish-cbc”, “[email protected]”, and “cast128-cbc”. The default is:
aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
aes256-cbc,arcfour,[email protected]
MACs Specifies the available MAC (message authentication code) algorithms. The MAC algorithm is used in protocol version 2 for data
integrity protection. Multiple algorithms must be comma-separated. The default is:
hmac-md5,hmac-sha1,[email protected],
hmac-ripemd160,hmac-sha1-96,hmac-md5-96,
hmac-sha2-256,hmac-sha2-512,[email protected] 3. Riavvia il servizio sshd.
# service sshd restart ### For CentOS/RHEL 6 # systemctl restart sshd ### For CentOS/RHEL 7