Cisco's Unified Communications Manager IM & Presence Service (Unified CM IM&P) is an integral component of many enterprise communications systems. Recently, a vulnerability (CVE-2023-20108) has been discovered in the XCP Authentication Service of the Cisco Unified CM IM&P, which could potentially allow an unauthenticated, remote attacker to cause a temporary service outage, resulting in a denial of service (DoS) condition for all users attempting to authenticate to the service.

This blog post will provide a comprehensive overview of the vulnerability, its exploitation details, and a code snippet to help understand the issue. Links to original references are provided at the end of the post for further investigation.

Exploit Details

The vulnerability in question (CVE-2023-20108) is caused by improper validation of user-supplied input. An attacker could exploit this vulnerability by sending a crafted login message to the affected device. A successful exploit could allow the attacker to cause an unexpected restart of the authentication service, preventing new users from successfully authenticating. It is important to note that exploitation of this vulnerability does not impact Cisco Unified CM IM&P users who were authenticated prior to an attack.

Code Snippet

A sample crafted login message that could exploit the CVE-2023-20108 vulnerability might look like the following:

import socket

TARGET_IP = "192..2.1"

malicious_login_message = "<?xml version=\"1.\" encoding=\"UTF-8\"?>" \
                          "<xcp-login-message version=\"1.\">" \
                          "<malicious_payload_here/>" \

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((TARGET_IP, TARGET_PORT))
sock.sendall(bytes(malicious_login_message, "utf-8"))

The above Python script demonstrates how an attacker might programmatically create a malicious login message and send it to the targeted device to exploit the vulnerability.

Original References

- Cisco Advisory: Cisco Unified Communications Manager IM & Presence Service Denial of Service Vulnerability
- CVE Details: CVE-2023-20108
- NIST National Vulnerability Database: CVE-2023-20108 Detail


CVE-2023-20108 is a critical vulnerability that affects the XCP Authentication Service of the Cisco Unified Communications Manager IM & Presence Service. By sending a crafted login message to an affected device, an attacker could potentially exploit the vulnerability and disrupt the authentication service for new user logins. It is essential for affected organizations to carefully review the issue and apply appropriate fixes or mitigations to protect their networks from potential attacks.


Published on: 06/28/2023 15:15:00 UTC
Last modified on: 07/12/2023 16:15:00 UTC