You set up a bastion host in your Virtual Cloud Network (VCN) to allow only your IP ad-dress (140.19.2.140) to establish SSH connections with your…

The Network Security Group (NSG) for the bastion host contains two ingress rules for TCP port 22. The first rule correctly allows access from the specific IP address 140.19.2.140/32. The second rule, however, allows access from the source NSG-050504. This means any resource, such as a compute instance, that is associated with NSG-050504 is permitted to establish an SSH connection to the bastion host. This explains why IPs other than the intended one are seen in the logs.

A. Access is not unrestricted; it is restricted to the two sources defined in the NSG rules. The issue is that one of the sources is broader than intended.
C. While a Security List could also be a cause, the information provided points directly to a permissive rule within the bastion's own NSG, making it the most direct root cause.
D. A /32 netmask correctly specifies a single IP address. It does not allow access from any other IP address in the network. This statement is factually incorrect.

1. Oracle Cloud Infrastructure Documentation, "Network Security Groups". "Network security groups (NSGs) act as a virtual firewall for your compute instances and other kinds of resources... An NSG consists of a set of ingress and egress security rules that apply only to the resources in that group... For example: you can group together a set of compute instances that have the same security posture, and then use the NSG as the source or destination for security rules."