Information
This variable limits the ciphers that SSH can use during communication.
Notes:
Some organizations may have stricter requirements for approved ciphers
Ensure that ciphers used are in compliance with site policy
The only 'strong' ciphers currently FIPS 140-2 compliant are:
aes256-ctr
aes192-ctr
aes128-ctr
Supported ciphers in openSSH 8.2:
3des-cbc
aes128-cbc
aes192-cbc
aes256-cbc
aes128-ctr
aes192-ctr
aes256-ctr
[email protected]
[email protected]
[email protected]
Rationale:
Weak ciphers that are used for authentication to the cryptographic module cannot be relied upon to provide confidentiality or integrity, and system data may be compromised
The Triple DES ciphers, as used in SSH, have a birthday bound of approximately four billion blocks, which makes it easier for remote attackers to obtain cleartext data via a birthday attack against a long-duration encrypted session, aka a 'Sweet32' attack
Error handling in the SSH protocol; Client and Server, when using a block cipher algorithm in Cipher Block Chaining (CBC) mode, makes it easier for remote attackers to recover certain plaintext data from an arbitrary block of ciphertext in an SSH session via unknown vectors
Solution
Edit the /etc/ssh/sshd_config file add/modify the Ciphers line to contain a comma separated list of the site approved ciphers
Example:
Ciphers [email protected],[email protected],[email protected],aes256-ctr,aes192-ctr,aes128-ctr
Default Value:
Ciphers [email protected],aes128-ctr,aes192-ctr,aes256-ctr,[email protected],[email protected]