The SSH daemon must be configured to not use Cipher-Block Chaining (CBC) ciphers.

From Oracle Linux 5 Security Technical Implementation Guide

Associated with: CCI-000366

SV-63567r1_rule The SSH daemon must be configured to not use Cipher-Block Chaining (CBC) ciphers.

Vulnerability discussion

The Cipher-Block Chaining (CBC) mode of encryption as implemented in the SSHv2 protocol is vulnerable to chosen plain text attacks and must not be used.

Check content

Check the SSH daemon configuration for allowed ciphers. # grep -i ciphers /etc/ssh/sshd_config | grep -v '^#' If no lines are returned, or the returned ciphers list contains any cipher ending with cbc, this is a finding.

Fix text

Edit /etc/ssh/sshd_config and add or edit the "Ciphers" line. Only include ciphers that start with "3des" or "aes" and do not contain "cbc". For the list of available ciphers for the particular version of your software, consult the sshd_config manpage. Restart the SSH daemon.

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