Increased latency for internet traffic (A): While overlapping CIDR blocks can have routing complexities, latency increase is not the primary security concern.
Subnet resource conflicts (B): This might occur due to overlapping address spaces, but it,s not the most critical security risk.
Potential routing issues within the VCN (C): Overlapping CIDRs can indeed create routing issues, but again, not the biggest security concern.
Exposure of private resources (D): This is the major security risk. With shared CIDR blocks, routing can become ambiguous, potentially allowing public internet traffic to inadvertently reach private resources within the VCN, compromising their security.
Why is this risky?
Any misconfiguration or security exploit could potentially expose private resources like databases or internal servers directly to the public internet.
This can lead to unauthorized access, data breaches, and other security vulnerabilities.