The correct options are:
A. An attacker could potentially perform a downgrade attack.
- When both strong and weak ciphers are configured on a VPN concentrator, an attacker could potentially force the connection to use weaker encryption by performing a downgrade attack. This increases the vulnerability of the connection.
C. The integrity of the data could be at risk.
- Weak ciphers may not provide sufficient protection for the integrity of the data being transmitted. Thus, when weak ciphers are configured alongside strong ciphers, the integrity of the data could indeed be at risk.