The Cisco router must be configured to implement replay-resistant authentication mechanisms for network access to privileged accounts.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-96249	CISC-ND-000530	SV-105387r1_rule		Medium

Description
A replay attack may enable an unauthorized user to gain access to the application. Authentication sessions between the authenticator and the application 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. Techniques used to address this include protocols using nonces (e.g., numbers generated for a specific one-time use) or challenges (e.g., TLS, WS_Security). Additional techniques include time-synchronous or challenge-response one-time authenticators.

Description

A replay attack may enable an unauthorized user to gain access to the application. Authentication sessions between the authenticator and the application 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. Techniques used to address this include protocols using nonces (e.g., numbers generated for a specific one-time use) or challenges (e.g., TLS, WS_Security). Additional techniques include time-synchronous or challenge-response one-time authenticators.

STIG	Date
Cisco IOS XE Router NDM Security Technical Implementation Guide	2019-07-25

Details

Check Text ( C-95083r1_chk )
Review the Cisco router configuration to verify that SSH is configured to use FIPS-140-2 compliant HMACs as shown in the example below. ip ssh version 2 ip ssh server algorithm encryption aes128-cbc aes192-cbc aes192-ctr Note: An SSH configuration enables a server and client to authorize the negotiation of only those algorithms that are configured from the allowed list. If a remote party tries to negotiate using an algorithm that is not part of the allowed list, the request is rejected and the session is not established. If the router is not configured to implement replay-resistant authentication mechanisms for network access to privileged accounts, this is a finding.

Check Text ( C-95083r1_chk )

Review the Cisco router configuration to verify that SSH is configured to use FIPS-140-2 compliant HMACs as shown in the example below.

ip ssh version 2
ip ssh server algorithm encryption aes128-cbc aes192-cbc aes192-ctr

Note: An SSH configuration enables a server and client to authorize the negotiation of only those algorithms that are configured from the allowed list. If a remote party tries to negotiate using an algorithm that is not part of the allowed list, the request is rejected and the session is not established.

If the router is not configured to implement replay-resistant authentication mechanisms for network access to privileged accounts, this is a finding.

Fix Text (F-101925r1_fix)
Configure SSH to use FIPS-140-2 compliant HMACs as shown in the example below. R1(config)#ip ssh version 2 R1(config)#ip ssh server algorithm encryption aes128-cbc aes192-cbc aes192-ctr Note: An SSH configuration enables a server and client to authorize the negotiation of only those algorithms that are configured from the allowed list. If a user tries to negotiate using an algorithm that is not part of the allowed list, the request is rejected and the session is not established.

Fix Text (F-101925r1_fix)

Configure SSH to use FIPS-140-2 compliant HMACs as shown in the example below.

R1(config)#ip ssh version 2
R1(config)#ip ssh server algorithm encryption aes128-cbc aes192-cbc aes192-ctr

Note: An SSH configuration enables a server and client to authorize the negotiation of only those algorithms that are configured from the allowed list. If a user tries to negotiate using an algorithm that is not part of the allowed list, the request is rejected and the session is not established.