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5.2.12 Ensure sshd KexAlgorithms is configured
Information
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 receivedMore information about the openSSH server configuration is available in the "Configure SSH Server" section overview.
Key exchange methods that are considered weak should be removed. A key exchange method may be weak because too few bits are used, or the hashing algorithm is considered too weak. Using weak algorithms could expose connections to man-in-the-middle attacks
Solution
Edit the /etc/ssh/sshd_config file and add/modify the KexAlgorithms line to contain a comma separated allow list of the site approved (strong) KexAlgorithms:Example:
KexAlgorithms curve25519-sha256,[email protected],ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256
See Also
Item Details
Audit Name: CIS Amazon Linux 2 v4.0.0 L1 Server
Category: ACCESS CONTROL, IDENTIFICATION AND AUTHENTICATION, SYSTEM AND COMMUNICATIONS PROTECTION
References: 800-53|AC-17(2), 800-53|IA-5, 800-53|IA-5(1), 800-53|SC-8, 800-53|SC-8(1), CSCv7|14.4
Plugin: Unix
Control ID: 58a4fec476e1072aca2bc818aac026e15a10efc2c2af3906fd6b13b7866428d5