CVE-2023-20154: Cisco Modeling Labs Auth Bypass Flaw

CVE-2023-20154 Overview

A vulnerability in the external authentication mechanism of Cisco Modeling Labs could allow an unauthenticated, remote attacker to access the web interface with administrative privileges. This vulnerability is due to the improper handling of certain messages that are returned by the associated external authentication server.

An attacker could exploit this vulnerability by logging in to the web interface of an affected server. Under certain conditions, the authentication mechanism would be bypassed and the attacker would be logged in as an administrator. A successful exploit could allow the attacker to obtain administrative privileges on the web interface of an affected server, including the ability to access and modify every simulation and all user-created data.

Critical Impact

Remote attackers with valid external authentication credentials can bypass authentication controls and gain full administrative access to Cisco Modeling Labs, enabling complete control over simulations and user data.

Affected Products

• Cisco Modeling Labs (all vulnerable versions)

Discovery Timeline

• 2024-11-15 - CVE CVE-2023-20154 published to NVD
• 2025-08-05 - Last updated in NVD database

Technical Details for CVE-2023-20154

Vulnerability Analysis

This authentication bypass vulnerability (CWE-305: Authentication Bypass by Primary Weakness) affects the external authentication mechanism in Cisco Modeling Labs. The vulnerability stems from improper handling of certain messages returned by external authentication servers, which can lead to a complete bypass of the authentication mechanism under specific conditions.

When a user attempts to authenticate through the web interface using external authentication (such as LDAP or RADIUS), the application fails to properly validate or handle certain response messages from the authentication server. This flaw allows an attacker who possesses valid user credentials stored on the external authentication server to be incorrectly elevated to administrator privileges during the login process.

The attack is network-accessible and requires low complexity to execute, though the attacker must possess valid user credentials on the external authentication system. Successful exploitation grants administrative access to the web interface, compromising both confidentiality and integrity of all simulations and user-created data within the affected Cisco Modeling Labs instance.

Root Cause

The root cause of this vulnerability lies in the improper message handling logic within Cisco Modeling Labs' external authentication integration. When processing authentication responses from external servers (such as LDAP, RADIUS, or other supported authentication backends), the application fails to correctly interpret or validate specific message types or conditions. This improper handling results in the authentication mechanism being bypassed, incorrectly granting administrative privileges to users who should only have standard access rights.

Attack Vector

The attack vector is network-based and requires the following conditions:

1. The target Cisco Modeling Labs instance must be configured to use external authentication
2. The attacker must have valid user credentials stored on the external authentication server
3. The attacker initiates a login request to the web interface
4. Under certain conditions related to the external authentication server's response, the authentication bypass occurs
5. The attacker is logged in with administrator privileges instead of their assigned role

This vulnerability requires low attack complexity and no user interaction. The attacker gains the ability to access and modify all simulations and user-created data within the affected system.

Detection Methods for CVE-2023-20154

Indicators of Compromise

• Unexpected administrative account logins from users who should have standard privileges
• Anomalous authentication logs showing privilege escalation events during external authentication
• Unusual modifications to simulations or user data by accounts that should not have administrative access
• Authentication server logs showing successful authentication followed by unauthorized administrative actions in Cisco Modeling Labs

Detection Strategies

• Monitor authentication logs for users gaining administrative access when their external authentication profile should grant lower privileges
• Implement alerting for any administrative actions performed by accounts that are not designated as administrators in the external authentication system
• Review audit logs for bulk modifications or access to simulations and user data following authentication events
• Cross-reference external authentication server logs with Cisco Modeling Labs access logs to identify privilege discrepancies

Monitoring Recommendations

• Enable verbose logging for authentication events in Cisco Modeling Labs
• Configure SIEM rules to correlate external authentication events with subsequent administrative actions
• Implement real-time alerting for administrative privilege grants during external authentication flows
• Regularly audit user privilege assignments and compare against expected roles in the external authentication system

How to Mitigate CVE-2023-20154

Immediate Actions Required

• Review the Cisco Security Advisory for specific version details and remediation guidance
• Identify all Cisco Modeling Labs instances using external authentication mechanisms
• Apply the latest security patches released by Cisco that address this vulnerability
• Consider temporarily switching to local authentication until patches can be applied

Patch Information

Cisco has released software updates that address this vulnerability. Administrators should consult the Cisco Security Advisory for detailed patch information, including fixed software versions and upgrade instructions. Organizations should prioritize patching given the potential for unauthorized administrative access.

Workarounds

• According to Cisco, workarounds are available that address this vulnerability; consult the security advisory for specific workaround instructions
• Consider restricting network access to the Cisco Modeling Labs web interface to trusted networks only
• Implement additional network segmentation to limit exposure of vulnerable instances
• Deploy web application firewalls to monitor and filter authentication traffic

# Verify current Cisco Modeling Labs version
# Consult Cisco Security Advisory for fixed versions:
# https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-cml-auth-bypass-4fUCCeG5

# Restrict access to management interface (example using iptables)
iptables -A INPUT -p tcp --dport 443 -s <trusted_network> -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP