CVE-2024-20254: Cisco Expressway CSRF Vulnerability

CVE-2024-20254 Overview

CVE-2024-20254 is a Cross-Site Request Forgery (CSRF) vulnerability affecting Cisco Expressway Series and Cisco TelePresence Video Communication Server (VCS). This vulnerability allows an unauthenticated, remote attacker to conduct CSRF attacks that perform arbitrary actions on an affected device. The vulnerability impacts both Cisco Expressway Control (Expressway-C) and Cisco Expressway Edge (Expressway-E) devices.

Critical Impact

Successful exploitation could allow attackers to perform arbitrary actions on affected Cisco Expressway devices with the privileges of the targeted user, potentially leading to complete compromise of confidentiality, integrity, and availability.

Affected Products

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

Discovery Timeline

• 2024-02-07 - CVE-2024-20254 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-20254

Vulnerability Analysis

This CSRF vulnerability exists in the web-based management interface of Cisco Expressway Series and TelePresence VCS devices. The vulnerability stems from insufficient CSRF protections in the management interface, which fails to properly validate requests to ensure they originate from legitimate user interactions. When exploited, an attacker can trick an authenticated administrator into clicking a malicious link or visiting a malicious webpage, which then submits unauthorized requests to the vulnerable device using the victim's authenticated session.

The impact of successful exploitation is significant—an attacker could perform any administrative action that the victim user is authorized to perform, including modifying device configurations, creating new user accounts, or changing security settings.

Root Cause

The root cause of CVE-2024-20254 is a weakness in the CSRF protection mechanisms (CWE-352) implemented in the Cisco Expressway web management interface. The application fails to include or validate anti-CSRF tokens in state-changing requests, allowing forged requests from malicious websites to be processed as legitimate when a victim with an active session is tricked into triggering them.

Attack Vector

The attack requires user interaction where an authenticated administrator must be tricked into accessing a malicious resource (link, webpage, or embedded content) while having an active session on the Cisco Expressway management interface. The attacker crafts a malicious request targeting the vulnerable endpoint and embeds it within a webpage or link. When the victim accesses this resource, their browser automatically includes their session credentials, causing the forged request to execute with the victim's privileges.

The vulnerability is exploitable over the network and does not require authentication from the attacker's perspective—only that the victim be authenticated. Attack scenarios commonly involve:

• Phishing emails containing malicious links targeting Expressway administrators
• Watering hole attacks on websites frequented by network administrators
• Malicious advertisements or embedded iframes on compromised websites

Detection Methods for CVE-2024-20254

Indicators of Compromise

• Unexpected configuration changes on Cisco Expressway devices without corresponding administrator activity
• Suspicious login sessions or administrative actions occurring at unusual times
• Web server logs showing requests to management endpoints originating from external referrers
• Unauthorized user accounts or privilege modifications in the Expressway admin console

Detection Strategies

• Review Cisco Expressway audit logs for configuration changes that cannot be attributed to known administrative activity
• Monitor network traffic for unusual patterns of requests to the Expressway management interface, particularly those with external referrer headers
• Implement web application firewall rules to detect and block requests with suspicious cross-origin characteristics
• Configure SIEM alerts for administrative actions on Expressway devices that occur outside of maintenance windows

Monitoring Recommendations

• Enable comprehensive logging on Cisco Expressway devices and forward logs to a centralized SIEM platform
• Establish baselines for normal administrative activity and alert on deviations
• Monitor for changes to critical configurations such as user accounts, certificates, and network settings
• Implement network segmentation to restrict access to management interfaces and monitor cross-segment traffic

How to Mitigate CVE-2024-20254

Immediate Actions Required

• Apply the security patches provided by Cisco as detailed in the Cisco Security Advisory
• Restrict access to the Cisco Expressway management interface to trusted networks only
• Educate administrators about phishing risks and the importance of not clicking unknown links while logged into management interfaces
• Review recent configuration changes and audit logs for any signs of compromise

Patch Information

Cisco has released software updates that address this vulnerability. Administrators should consult the Cisco Security Advisory for specific version information and upgrade instructions. Organizations should prioritize patching given the network-accessible nature of the vulnerability and the potential impact of successful exploitation.

Workarounds

• Limit management interface access to a dedicated, isolated management network segment
• Implement strict network access controls (ACLs) to allow only authorized IP addresses to reach the management interface
• Use separate browser sessions or browsers for administrative tasks—avoid general web browsing while logged into Cisco Expressway
• Consider implementing additional authentication factors for administrative access where supported

# Example: Restrict management interface access using firewall rules
# Allow only trusted management networks to access Expressway admin interface
iptables -A INPUT -p tcp --dport 443 -s 10.10.10.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP