How to Fix CVE-2024-20375 - A High Denial of Service Vulnerability in Cisco Unified CM?

Cisco has recently disclosed a critical vulnerability in its Unified Communications Manager (Unified CM) and Unified Communications Manager Session Management Edition (Unified CM SME) products. This high-severity flaw, tracked as CVE-2024-20375, could allow an unauthenticated remote attacker to cause a denial of service (DoS) condition on affected devices. With a CVSS score of 8.6, this vulnerability poses a significant risk to organizations using Cisco's communication infrastructure. In this article, we'll dive deep into the details of CVE-2024-20375, its potential impact, affected products, and most importantly, how to mitigate and fix this vulnerability to ensure the security and stability of your Cisco Unified Communications environment.

A Short Introduction to Cisco Unified Communications Manager

Cisco Unified Communications Manager (Unified CM) is a core component of Cisco's enterprise communication solutions. It serves as the call control and session management platform for voice, video, messaging, and mobility applications. Unified CM provides essential features for IP telephony and unified communications, including:

Unified CM is designed to scale from small businesses to large enterprises, supporting thousands of users and devices. It plays a crucial role in ensuring seamless communication across an organization's network, making it a critical infrastructure component for many businesses worldwide.

The Session Management Edition (SME) is a specialized deployment model of Unified CM that focuses on centralized dial plan management and call routing between multiple Unified CM clusters, legacy PBX systems, and other voice gateways.

Summary of the Vulnerability

This vulnerability exists in the SIP call processing function of Cisco Unified CM and Unified CM SME. It stems from improper parsing of SIP (Session Initiation Protocol) messages, which are fundamental to VoIP communications. An unauthenticated, remote attacker could exploit this vulnerability by sending a crafted SIP message to an affected device.

The root cause of the vulnerability appears to be related to an out-of-bounds write condition (CWE-787) in the SIP message parsing logic. This suggests that the Unified CM software fails to properly validate or sanitize incoming SIP messages, potentially allowing malformed data to be written to memory locations outside the intended buffer. Such memory corruption can lead to unexpected behavior, including system crashes or reboots.

When successfully exploited, this vulnerability could allow an attacker to cause the affected device to reload, resulting in a denial of service condition. This DoS state would interrupt the communications of reliant voice and video devices across the organization's network, potentially bringing critical communication services to a halt.

Impact of the Vulnerability

The potential impact of CVE-2024-20375 is severe, given the critical nature of Unified CM in enterprise communications infrastructure. Here are the key consequences of a successful exploit:

Given these potential impacts, it's crucial for organizations using Cisco Unified CM or Unified CM SME to take immediate action to mitigate and patch this vulnerability.

Products Affected by the Vulnerability

According to Cisco's security advisory, the following products are affected by CVE-2024-20375:

It's important to note that this vulnerability affects these products regardless of their specific configuration. This means that all deployments of Unified CM and Unified CM SME running vulnerable versions are at risk, regardless of any custom settings or deployment models.It's important to note that this vulnerability affects these products regardless of their specific configuration. This means that all deployments of Unified CM and Unified CM SME running vulnerable versions are at risk, regardless of any custom settings or deployment models.

Cisco has also confirmed that the following products are not affected by this vulnerability:

While these products are not directly vulnerable, it's worth noting that they may still be indirectly affected if they rely on a vulnerable Unified CM instance for call processing or other services.

How to Check Your Product is Vulnerable?

To determine if your Cisco Unified Communications Manager or Unified CM SME is vulnerable to CVE-2024-20375, follow these steps:

2. Compare your version to the affected versions:

3. Check for signs of exploitation:

4. Assess your exposure:

5. Consult Cisco documentation:

By following these steps, you can accurately assess whether your Cisco Unified Communications environment is at risk from this vulnerability and take appropriate action.

How to Fix the Vulnerability?

To address the CVE-2024-20375 vulnerability in Cisco Unified Communications Manager and Unified CM SME, follow these steps:

1. Upgrade to a Fixed Version: Cisco has released software updates that address this vulnerability. Upgrade your Unified CM or Unified CM SME to one of the following fixed versions:

2. To perform the upgrade: a. Download the appropriate update from the Cisco Software Download page. b. Follow the upgrade procedure in the Cisco Unified Communications Manager Upgrade Guide for your specific version. c. Ensure you have a current backup of your system before initiating the upgrade. d. Plan for a maintenance window, as the upgrade process will require a system restart.

3. Apply Temporary Mitigation Measures: While there are no official workarounds provided by Cisco, you can implement the following measures to reduce the risk of exploitation: a. Implement strict access controls:

4. b. Monitor and rate-limit SIP traffic:

5. c. Enable logging and monitoring:

6. -Upgrade Verification: After upgrading to a fixed version: a. Verify the new version is correctly installed by checking the "Active Version" in the Unified CM Administration interface. b. Test core functionality to ensure all services are operating correctly. c. Monitor system logs for any signs of continued exploitation attempts or unusual behavior

7. Long-term Security Measures: To improve overall security and resilience against similar vulnerabilities: a. Implement a regular patching schedule for all Cisco Unified Communications components. b. Conduct periodic security assessments of your VoIP infrastructure. c. Consider implementing a layered security approach, using session border controllers and other security appliances to protect your Unified CM deployment. d. Keep abreast of Cisco security advisories and industry best practices for VoIP security.

8. Report Any Issues: If you encounter any problems during the upgrade process or suspect ongoing exploitation:

Remember, there are no workarounds that fully address this vulnerability, so applying the software update is the only complete solution. Prioritize this update, especially for Unified CM instances that are critical to your organization's communication infrastructure or those that may be more exposed to potential attacks.

By following these steps and maintaining ongoing vigilance, you can effectively mitigate the risk posed by CVE-2024-20375 and enhance the overall security of your Cisco Unified Communications environment.

This vulnerability serves as a reminder of the importance of keeping critical communication infrastructure up-to-date and properly secured. Regular security assessments, prompt patching, and following vendor-recommended best practices are key to maintaining a robust and resilient unified communications system.

We hope this post helps explores the details of CVE-2024-20375, its summary, potential impact, and provide guidance on how to protect your Cisco Unified CM. Thanks for reading this post. Please share this post and help secure the digital world.Visit our website thesecmaster.com, and our social media page on Facebook, LinkedIn, Twitter, Telegram, Tumblr, Medium, and Instagram and subscribe to receive updates like this.

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