{"description": "Limit the MACs to strong hash algorithms.\nThe following line in <tt>/etc/ssh/sshd_config</tt> demonstrates use\nof those MACs:\n<pre>MACs <sub idref=\"sshd_strong_macs\" /></pre>", "rationale": "MD5 and 96-bit MAC algorithms are considered weak and have been shown to increase\nexploitability in SSH downgrade attacks. Weak algorithms continue to have a great deal of\nattention as a weak spot that can be exploited with expanded computing power. An\nattacker that breaks the algorithm could take advantage of a MiTM position to decrypt the\nSSH tunnel and capture credentials and information", "severity": "medium", "references": {"nist": ["AC-17 (2)"], "srg": ["SRG-OS-000250-GPOS-00093"], "cis": ["5.1.15"]}, "control_references": {"cis": ["5.1.15"]}, "components": [], "identifiers": {}, "ocil_clause": "MACs option is commented out or not using strong hash algorithms", "ocil": "Only strong MACs should be used. To verify that only strong\nMACs are in use, run the following command:\n<pre>$ sudo grep -i macs /etc/ssh/sshd_config</pre>\nThe output should contain only those MACs which are strong, namely,\n<sub idref=\"sshd_strong_macs\" /> hash functions.", "oval_external_content": null, "fixtext": "", "checktext": "", "vuldiscussion": "", "srg_requirement": "", "warnings": [], "conflicts": [], "requires": [], "policy_specific_content": {}, "platform": null, "platforms": [], "sce_metadata": {}, "inherited_platforms": ["system_with_kernel"], "cpe_platform_names": [], "inherited_cpe_platform_names": ["system_with_kernel"], "bash_conditional": null, "fixes": {}, "title": "Use Only Strong MACs", "definition_location": "/aptdata/openscap/scap-security-guide/linux_os/guide/services/ssh/ssh_server/sshd_use_strong_macs/rule.yml", "template": null}