I agree with the suggested answer, which is D. Configuring IPS and WAF with signatures.
Reasoning:
The question requires a solution that mitigates a vulnerability without interrupting service. Configuring an Intrusion Prevention System (IPS) and a Web Application Firewall (WAF) with appropriate signatures is the best approach because it allows the banking application to remain operational while actively blocking or mitigating exploit attempts targeting the vulnerable runtime engine. This offers a balance between security and availability during the transition period. An IPS can detect and prevent malicious network activity, while a WAF can filter and block malicious HTTP/HTTPS traffic.
Reasons for not choosing the other options:

A. Shutting down the systems until the code is ready: This option ensures security but interrupts the service, which contradicts the requirement to avoid interruption.
B. Uninstalling the impacted runtime engine: This option would also interrupt the service, as the application depends on it, and thus is not an appropriate option during the transition.
C. Selectively blocking traffic on the affected port: While this can mitigate some risk, it may also block legitimate traffic and might not be as effective as an IPS/WAF in detecting and preventing complex attacks. It is also less adaptable to different attack vectors compared to signature-based detection.

The combination of IPS and WAF provides layered security, addressing both network-level and application-level threats without causing downtime, therefore making it the most suitable choice.

Suggested Answer: D

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