CVE-2023-20105: Cisco VCS Privilege Escalation Flaw

CVE-2023-20105 Overview

A privilege escalation vulnerability exists in the change password functionality of Cisco Expressway Series and Cisco TelePresence Video Communication Server (VCS). This vulnerability allows an authenticated, remote attacker with Read-only credentials to elevate privileges to Administrator on an affected system by exploiting incorrect handling of password change requests.

The vulnerability stems from improper input validation in the web-based management interface when processing password change requests. An attacker who has already authenticated to the application as a Read-only user can send a crafted request to alter the passwords of any user on the system, including administrative users, and subsequently impersonate those accounts.

Critical Impact

Authenticated attackers with minimal Read-only access can escalate to full Administrator privileges by manipulating password change requests, potentially gaining complete control over Cisco Expressway and TelePresence VCS deployments.

Affected Products

• Cisco Expressway Series (Expressway-C and Expressway-E)
• Cisco TelePresence Video Communication Server (VCS)

Discovery Timeline

• June 28, 2023 - CVE-2023-20105 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-20105

Vulnerability Analysis

This privilege escalation vulnerability is classified under CWE-20 (Improper Input Validation). The flaw exists in the password change functionality of the web-based management interface. When a Read-only user submits a password change request, the application fails to properly validate that the user should only be able to modify their own credentials. This authorization gap allows low-privileged users to target any account on the system.

The attack is network-accessible and requires low privilege (authenticated Read-only access), but no user interaction is needed. While confidentiality is not directly impacted, the integrity impact is high as attackers can modify critical authentication data for any user account on the system.

Root Cause

The root cause lies in incorrect handling of password change requests within the web-based management interface. The application does not properly enforce authorization checks to verify that the authenticated user has permission to change the password of the targeted account. This allows any authenticated user, regardless of their privilege level, to submit password change requests for arbitrary users including administrators.

Attack Vector

The attack vector is network-based, targeting the web-based management interface of Cisco Expressway Series or TelePresence VCS. An attacker first authenticates to the application using valid Read-only credentials—which may be obtained through credential theft, social engineering, or legitimate access. Once authenticated, the attacker crafts a malicious password change request that specifies a target user (typically an administrator account) and a new password. Due to the improper input validation, the system processes this request and changes the target user's password, allowing the attacker to then log in as that user with elevated privileges.

The exploitation sequence involves:

1. Authenticating to the web management interface with Read-only credentials
2. Crafting a modified password change request targeting an administrator account
3. Sending the crafted request to the web-based management interface
4. Authenticating with the newly set administrator password to gain elevated access

Detection Methods for CVE-2023-20105

Indicators of Compromise

• Unexpected password change events for administrator or privileged accounts in system logs
• Authentication attempts from Read-only user sessions followed by administrative session establishments
• Multiple failed login attempts for administrative accounts followed by successful authentication
• Audit log entries showing password modifications initiated by low-privilege users

Detection Strategies

• Monitor authentication logs for privilege escalation patterns where Read-only users subsequently appear with administrative access
• Implement alerting on password change events for administrative accounts, especially when initiated through the web interface
• Review web server access logs for unusual patterns in requests to password management endpoints
• Correlate user session data to identify accounts that transition from Read-only to Administrator roles unexpectedly

Monitoring Recommendations

• Enable comprehensive audit logging on Cisco Expressway and TelePresence VCS systems
• Configure SIEM rules to detect anomalous password change activities targeting administrative accounts
• Implement real-time alerting for any administrative password modifications
• Regularly review access control lists and user privilege assignments

How to Mitigate CVE-2023-20105

Immediate Actions Required

• Review the Cisco Security Advisory for affected version details and upgrade guidance
• Audit all user accounts to identify and remove unnecessary Read-only access
• Reset passwords for all administrative accounts as a precaution
• Monitor for any signs of unauthorized privilege escalation in system logs

Patch Information

Cisco has released software updates to address this vulnerability. Administrators should consult the Cisco Security Advisory (cisco-sa-expressway-priv-esc-Ls2B9t7b) for specific fixed software versions and upgrade instructions. Organizations should prioritize patching based on exposure and criticality of their Expressway and TelePresence VCS deployments.

Workarounds

• Restrict network access to the web-based management interface using firewall rules or access control lists
• Limit Read-only account provisioning to only essential personnel with verified need
• Implement network segmentation to isolate management interfaces from general network access
• Consider disabling web-based management access when not actively in use for configuration changes

# Example: Restrict management interface access via firewall (adjust IPs as needed)
# Allow management access only from trusted administrator workstations
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP