Published: June 2024

Author: AI Security Insights

A significant threat has emerged in the world of network infrastructure with the discovery of CVE-2023-20186, a vulnerability that impacts major Cisco operating systems—Cisco IOS Software and Cisco IOS XE Software. The flaw blends authentication and command authorization issues, targeting the Secure Copy Protocol (SCP) when used on Cisco devices with AAA (Authentication, Authorization, and Accounting) configured. Let's break this vulnerability down, look at how it can be exploited, and discuss how you can defend your network.

What is CVE-2023-20186?

This vulnerability is a result of improper command authorization when using the Secure Copy Protocol (SCP) on Cisco IOS and IOS XE devices with AAA enabled. An attacker with a valid user account and level 15 privilege can leverage SCP to bypass command restrictions, uploading or downloading any files—even configuration files—without proper authorization checks.

Devices with AAA command authorization configured

- Accounts with privilege level 15 (full admin/root-level access)

Environments where SCP is enabled as a file transfer method

If your network fits any of the bullet points above, read on carefully.

The Technical Root: AAA SCP Command Authorization Flaw

SCP allows secure file transfer over SSH. Under normal security policy, even administrators with level 15 access should be subject to configured AAA command controls—meaning, for instance, if command authorization is strict, file operations could be limited.

Cisco's internal handling of SCP commands does not properly check AAA restrictions.

- As a result, SCP operations are permitted even for users who should be denied for specific file operations on the system.

Scenario

Suppose "bob" is an administrative user but restricted from copying configuration files via AAA rules. Due to this bug, "bob" can still use SCP to copy files to/from the router's file system. This includes startup-config, running-config, or even replacement images.

Potential Impact

- Confidentiality breach: Downloading router configurations, revealing credentials and network secrets.
- Integrity violation: Uploading malicious config files or binaries, tampering with device operation.

Proof-of-Concept: Demonstrating the Issue

Below is a simple walkthrough that shows how an attacker might exploit CVE-2023-20186 given valid device admin credentials.

Step 1: Prepare SCP client

On the attacker's machine (Linux or Mac), open terminal.

# To download the running configuration:
scp attacker@10...1:running-config ./stolen-config.txt

# To upload a new malicious configuration:
scp ./malicious-config.txt attacker@10...1:startup-config

Server log excerpt

%SEC_LOGIN-5-LOGIN_SUCCESS: Login Success [user: attacker] [Source: 192.168.1.10] ...
%SCP-6-SCPUPLOAD: File 'startup-config' opened by user attacker for upload

Key point: Even if AAA command authorization is intended to prevent access, the attacker bypasses these protections using SCP.

Cisco Security Advisory:

Cisco IOS and IOS XE Software Authentication, Authorization, and Accounting File Transfer Vulnerability

NIST NVD Entry:

CVE-2023-20186 on NVD

Community Writeups:

Redteam Notes on CVE-2023-20186 (External Blog)

1. Update Your Devices

Cisco has released patches for affected versions. Upgrade IOS and IOS XE to the latest recommended releases. See Cisco’s advisory link above for exact versions.

If you don't need SCP for file transfers, disable it

conf t
no ip scp server enable
end
write mem

3. Restrict Admin Access

Limit who has privilege level 15 and restrict SSH/SCP access to trusted network segments only.

ip access-list standard mgmtIP
 permit 192.168.10. ...255
!
line vty  4
 access-class mgmtIP in

4. Monitor and Audit Logs

Watch for unusual file transfer activity and non-standard SCP connections.

Summary

CVE-2023-20186 allows attackers to bypass AAA command authorization using SCP on Cisco IOS/IOS XE, giving them dangerous file access that could allow them to steal configs or implant malicious files. If you use Cisco devices with AAA and SCP, patch now, review privileges, and disable unwanted services.

Stay safe—patch fast, audit often!

*If you found this useful, share with your network/security team and keep up with Cisco advisories for ongoing protection.*

Footnotes

*This writeup is based on real-world attack scenarios and direct analysis of public advisories. For more deep dives, visit the Cisco PSIRT page and stay informed.*

Timeline

Published on: 09/27/2023 18:15:11 UTC
Last modified on: 10/06/2023 18:14:19 UTC