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September 3, 2024
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How to Fix CVE-2024-20375 - A High Denial of Service Vulnerability in Cisco Unified CM?


Critical Cisco UC Manager DoS Flaw Alert! CVE-2024-20375

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:

  • Call processing and routing

  • Device and user provisioning

  • Voicemail integration

  • Presence and instant messaging services

  • Integration with other Cisco collaboration tools

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

  • CVE ID: CVE-2024-20375

  • Description: Denial of Service Vulnerability in Cisco Unified Communications Manager

  • CVSS Score: 8.6 (High)

  • CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

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:

  1. Service Disruption: The primary impact is the potential for a complete disruption of voice and video communication services. As Unified CM is responsible for call processing and routing, a DoS condition could render an organization's entire IP telephony system inoperable.

  2. Business Continuity: For many organizations, reliable communication is essential for day-to-day operations. A DoS attack exploiting this vulnerability could significantly impact business continuity, affecting both internal collaboration and external customer interactions.

  3. Repeated Attacks: Since the vulnerability allows unauthenticated, remote exploitation, an attacker could potentially launch repeated DoS attacks, making it difficult to restore and maintain services until the vulnerability is patched.

  4. Resource Consumption: Continuous exploitation attempts could lead to increased CPU and memory usage on affected devices, potentially impacting performance even when attacks are unsuccessful.

  5. Indirect Security Risks: While the vulnerability itself doesn't lead to data theft or system compromise, the disruption it causes could potentially be used as a smokescreen for other attacks or to prevent security teams from responding to other incidents.

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:

Product
Affected Versions
Cisco Unified Communications Manager (Unified CM)
Versions prior to 12.5(1)SU9, 14SU4, and 15SU1
Cisco Unified Communications Manager Session Management Edition (Unified CM SME)
Versions prior to 12.5(1)SU9, 14SU4, and 15SU1

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:

  • CallManager Express (CME)

  • Emergency Responder

  • IOS Software

  • IOS XE Software

  • Jabber Client

  • Packaged Contact Center Enterprise (PCCE) (including Outbound Dialer)

  • Prime Collaboration Deployment (PCD)

  • Prime License Manager (PLM)

  • Unified Border Element (CUBE)

  • Unified Communications Manager IM & Presence Service (Unified CM IM&P)

  • Unified Contact Center Enterprise (UCCE) (including Outbound Dialer)

  • Unified Contact Center Express (UCCX)

  • Unified Customer Voice Portal (CVP)

  • Unity Connection

  • Virtualized Voice Browser (VVB)

  • Voice Extensible Markup Language (VXML) Gateway

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:

  1. Identify your current version:

  • Log in to the Cisco Unified CM Administration interface.

  • Navigate to "Help" > "About" or "System" > "Enterprise Parameters".

  • Note the "Active Version" listed.

2. Compare your version to the affected versions:

  • If your version is earlier than 12.5(1)SU9, 14SU4, or 15SU1, your system is vulnerable.

  • If you're running version 12.5(1), ensure you're on SU9 or later.

  • For version 14, confirm you're running SU4 or later.

  • For version 15, verify you're on SU1 or later.

3. Check for signs of exploitation:

  • Monitor system logs for unexpected reloads or crashes.

  • Look for any unusual spikes in SIP traffic or failed SIP message parsing in the logs.

  • Pay attention to any reports of intermittent communication issues from end-users.

4. Assess your exposure:

  • Determine if your Unified CM or Unified CM SME is accessible from untrusted networks, especially the internet.

  • Review your firewall rules and ensure that SIP traffic (typically on port 5060 for UDP/TCP and 5061 for TLS) is properly restricted.

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:

  • For version 12.5(1): Upgrade to 12.5(1)SU9 or later

  • For version 14: Upgrade to 14SU4 or later

  • For version 15: Upgrade to 15SU1 or later

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:

  • Use firewalls and access control lists (ACLs) to restrict SIP traffic to trusted sources only.

  • Ensure that Unified CM is not directly exposed to the internet or untrusted networks.

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

  • Implement intrusion detection/prevention systems (IDS/IPS) to detect and block abnormal SIP traffic patterns.

  • Use SIP-aware security appliances or session border controllers (SBCs) to filter and validate SIP messages before they reach Unified CM.

5. c. Enable logging and monitoring:

  • Configure detailed logging for SIP transactions on Unified CM.

  • Set up alerts for unexpected system reloads or high rates of SIP message parsing failures.

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 FacebookLinkedInTwitterTelegramTumblrMedium, and Instagram and subscribe to receive updates like this.

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Arun KL

Arun KL is a cybersecurity professional with 15+ years of experience in IT infrastructure, cloud security, vulnerability management, Penetration Testing, security operations, and incident response. He is adept at designing and implementing robust security solutions to safeguard systems and data. Arun holds multiple industry certifications including CCNA, CCNA Security, RHCE, CEH, and AWS Security.

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