Ensure sshd KexAlgorithms is configured

MediumLevel 1Automatedlinux

Description

Key exchange is any method in cryptography by which cryptographic keys are exchanged between two parties, allowing use of a cryptographic algorithm. If the sender and receiver wish to exchange encrypted messages, each must be equipped to encrypt messages to be sent and decrypt messages received Notes: • Kex algorithms have a higher preference the earlier they appear in the list • Some organizations may have stricter requirements for approved Key exchange algorithms • Ensure that Key exchange algorithms used are in compliance with site policy • The only Key Exchange Algorithms currently FIPS 14

How it is checked

Audit method: Shell command

shell

alt0() { o=$(bash -c 'sshd -T | grep -Pi -- '"'"'kexalgorithms\h+([^#\n\r]+,)?(diffie-hellman-group1- sha1|diffie-hellman-group14-sha1|diffie-hellman-group-exchange-sha1)\b'"'"'' 2>/dev/null); [ -z "$o" ] || { echo "step1: $o" | head -c 300; return 1; }; }; if alt0; then echo compliant; fi

Expected output: compliant

How it is fixed

Fix method: Guidance or infrastructure patch

Note: • First occurrence of an option takes precedence. • Though key_exchange may be configured through the KexAlgorithms option in the /etc/ssh/sshd_config file, it is recommended that the key_exchange available to openSSH server are configured through system-wide-crypto-policy • If the recommendations in the subsection "Configure system wide crypto policy" have been followed, this Audit should be in a passing state. Please review that section before following this Remediation Procedure • By default, system-wide-crypto-policy is applied to the openSSH server. If the following defaults don't exist due to modifications or upgrade from a earlier release, the system-wide-crypto-policy may not b…

Properties

Operating systems: rocky-10
Tags: cis-convertedlinux
Reference: CIS Rocky Linux 10 Benchmark v1.0.0 - 5.1.12

Check this host

Run this on a machine you are allowed to audit. The scan is read-only.

shell

tmaegis scan --target linux