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RHEL 8 SSH server must be configured to use only FIPS-validated key exchange algorithms.

Overview

Finding IDVersionRule IDIA ControlsSeverity
V-255924RHEL-08-040342SV-255924r1017372_ruleCCI-001453medium
Description
Without cryptographic integrity protections provided by FIPS-validated cryptographic algorithms, information can be viewed and altered by unauthorized users without detection. RHEL 8 incorporates system-wide crypto policies by default. The SSH configuration file has no effect on the ciphers, MACs, or algorithms unless specifically defined in the /etc/sysconfig/sshd file. The employed algorithms can be viewed in the /etc/crypto-policies/back-ends/opensshserver.config file. The system will attempt to use the first algorithm presented by the client that matches the server list. Listing the values "strongest to weakest" is a method to ensure the use of the strongest algorithm available to secure the SSH connection.
STIGDate
Red Hat Enterprise Linux 8 Security Technical Implementation Guide2025-05-14

Related Frameworks

1 mapping across 4 frameworks
SCF0 mappings

No source states a mapping between these directly.

Also reachable in 3 hops (1) derived by us, not asserted by any source

Each of these is a route we composed by chaining published mappings. No publisher states a relationship between the two endpoints.

NET-14.2Protection of Confidentiality / Integrity Using Encryption
1.00
NIST 800-530 mappings

No source states a mapping between these directly.

Also reachable in 2 hops (31) derived by us, not asserted by any source

Each of these is a route we composed by chaining published mappings. No publisher states a relationship between the two endpoints.

AC-17(1)Monitoring and Control
1.00
AC-17(2)Protection of Confidentiality and Integrity Using Encryption
1.00
AC-3Access Enforcement
1.00
CM-6Configuration Settings
1.00
CM-7Least Functionality
1.00
IA-2(8)Access to Accounts — Replay Resistant
1.00
IA-2(9)Network Access to Non-privileged Accounts — Replay Resistant
1.00
IA-3Device Identification and Authentication
1.00
IA-3(1)Cryptographic Bidirectional Authentication
1.00
IA-5(1)Password-based Authentication
1.00

+21 more (top 10 by confidence shown)

NIST 800-1710 mappings

No source states a mapping between these directly.

Also reachable in 3 hops (1) derived by us, not asserted by any source

Each of these is a route we composed by chaining published mappings. No publisher states a relationship between the two endpoints.

3.1.13
1.00
CCI1 mapping
CCI-001453
1.00

Details

Check Text (C-255924r1017372_chk)

Verify that the SSH server is configured to use only FIPS-validated key exchange algorithms: $ sudo grep -i kexalgorithms /etc/crypto-policies/back-ends/opensshserver.config CRYPTO_POLICY='-oKexAlgorithms=ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512' If the entries following "KexAlgorithms" have any algorithms defined other than "ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512", appear in different order than shown, or are missing or commented out, this is a finding.

Fix Text (F-59544r880732_fix)

Configure the SSH server to use only FIPS-validated key exchange algorithms by adding or modifying the following line in "/etc/crypto-policies/back-ends/opensshserver.config": -oKexAlgorithms=ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512 A reboot is required for the changes to take effect.