Unauthenticated Telnet Login for Cisco Devices

/ nkinternet

Someone shared some notes with me about a Cisco router in 175.45.178.0/24 that was allowing unauthenticated telnet connections:

  1. Multiple Subnets and Network Segmentation: The switch manages traffic across several IP address ranges (172.16.x.x, 172.25.x.x, 175.45.x.x, 192.168.x.x), indicating a complex network setup with multiple segments. This suggests a structured approach to organizing network resources, possibly reflecting different operational areas or security levels within the network.
  2. External Connectivity and Gateway Configuration: The default gateway is set to 172.25.1.25, acting as the primary exit point for traffic intending to reach the internet or an external network. This could indicate where to focus efforts on understanding how traffic flows out of this network and potentially how it’s managed or monitored.
  3. Static Routing to Specific IPs: The presence of static routes, especially those directing traffic to specific IP addresses outside the local subnets (175.45.178.163/32, 175.45.178.164/32, 175.45.178.165/32 via 192.168.10.10), could hint at designated paths for certain types of communications or connections to specific external services or networks. This might offer clues about strategic external connections or the organization of the network’s external communications.
  4. ARP Table Entries: The Address Resolution Protocol (ARP) table entries reveal devices that have been communicating through the switch, providing MAC addresses and corresponding IP addresses. Notably, there’s a mix of local and potentially external IP addresses, giving a snapshot of active devices or servers. This information could be valuable for mapping the network or identifying critical devices within it.
  5. Access Control Lists (ACLs): The existence of an ACL that permits UDP traffic universally might be indicative of specific applications or services that are prioritized within the network, such as streaming or VoIP services. Understanding the role of UDP in this network might reveal operational priorities or specific applications in use.
  6. VLAN Configuration: The detailed VLAN setup shows the network’s logical segmentation, which could correspond to different departments, security zones, or types of traffic. This level of detail provides a clearer picture of the network’s internal organization and possibly its scale and complexity.
  7. Device and Software Information: Device is a Cisco Catalyst 3560V2 running IOS version 12.2(58)SE2

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