The operating system must implement replay-resistant authentication mechanisms for network access to privileged and non-privileged accounts.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-67599	AOSX-11-000570	SV-82089r1_rule		Medium

Description
The SSH Version should be explicitly set to Version 2. Version 2 supports strong crypto and was rewritten from scratch to resolve several weaknesses in Version 1 that make it extremely vulnerable to attackers. The weaker crypto in Version 1 is potentially susceptible to certain forms of replay attacks. The system default is to only enable Version 2. A replay attack may enable an unauthorized user to gain access to the operating system. Authentication sessions between the authenticator and the operating system validating the user credentials must not be vulnerable to a replay attack. An authentication process resists replay attacks if it is impractical to achieve a successful authentication by recording and replaying a previous authentication message. Satisfies: SRG-OS-000112-GPOS-00057, SRG-OS-000113-GPOS-00058

Description

The SSH Version should be explicitly set to Version 2. Version 2 supports strong crypto and was rewritten from scratch to resolve several weaknesses in Version 1 that make it extremely vulnerable to attackers. The weaker crypto in Version 1 is potentially susceptible to certain forms of replay attacks. The system default is to only enable Version 2. A replay attack may enable an unauthorized user to gain access to the operating system. Authentication sessions between the authenticator and the operating system validating the user credentials must not be vulnerable to a replay attack. An authentication process resists replay attacks if it is impractical to achieve a successful authentication by recording and replaying a previous authentication message. Satisfies: SRG-OS-000112-GPOS-00057, SRG-OS-000113-GPOS-00058

STIG	Date
Apple OS X 10.11 Security Technical Implementation Guide	2017-07-11

Details

Check Text ( C-68165r2_chk )
To check which protocol is configured for sshd, run the following: /usr/bin/sudo /usr/bin/grep ^Protocol /etc/ssh/sshd_config If there is no result or the result is not "2", this is a finding.

Fix Text (F-73713r2_fix)
In order to make sure that "Protocol 2" is used by sshd, run the following command: /usr/bin/sudo /usr/bin/sed -i.bak 's/.Protocol./Protocol 2/' /etc/ssh/sshd_config