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

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-239913	SRG-APP-000156-NDM-000250	CASA-ND-000470	SV-239913r960993_rule	2024-08-22	2

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.

ℹ️ Check
Step 1: Verify that FIPS mode is enabled as shown in the example. fips enable Step 2: Verify only SSH is configured to only use FIPS-compliant ciphers and that Diffie-Hellman Group 14 is used for the key exchange as shown in the example below. ssh version 2 ssh cipher encryption fips ssh key-exchange group dh-group14-sha1 Note: The ASA only supports SSHv2. If the ASA is not configured to implement replay-resistant authentication mechanisms for network access, this is a finding.

ℹ️ Check

Step 1: Verify that FIPS mode is enabled as shown in the example. fips enable Step 2: Verify only SSH is configured to only use FIPS-compliant ciphers and that Diffie-Hellman Group 14 is used for the key exchange as shown in the example below. ssh version 2 ssh cipher encryption fips ssh key-exchange group dh-group14-sha1 Note: The ASA only supports SSHv2. If the ASA is not configured to implement replay-resistant authentication mechanisms for network access, this is a finding.

✔️ Fix
Step 1: Enable FIPS mode via the fips enable command. Step 2: Configure SSH to only use FIPS-compliant ciphers and Diffie-Hellman Group 14 for the key exchange. ASA(config)# ssh cipher encryption fips ASA(config)# ssh key-exchange group dh-group14-sha