Description

A newly disclosed high-severity vulnerability (CVE-2025-20152) has been identified in Cisco’s Identity Services Engine (ISE), specifically in the way it processes RADIUS authentication messages. The flaw allows unauthenticated remote attackers to cause a denial-of-service (DoS) condition by sending specially crafted RADIUS requests to network access devices (NADs) that rely on Cisco ISE for authentication services. This issue, rated with a CVSS score of 8.6, is present in Cisco ISE version 3.4, while earlier versions such as 3.3 and below are not affected. The vulnerability, which results from improper handling of RADIUS requests, can force the ISE system to restart, leading to potential service disruptions. The root cause lies in an out-of-bounds read error during the processing of malformed RADIUS packets. Since RADIUS is enabled by default in most Cisco ISE deployments, the risk is elevated for organizations that haven't made configuration changes. The attack requires no authentication or user interaction, making it easy to exploit. Although no active exploitation has been observed, the vulnerability’s presence in a widely-used network access control solution significantly increases the potential threat to enterprise environments, especially those heavily dependent on RADIUS for AAA services. Cisco has addressed the issue in the ISE 3.4P1 update and strongly urges affected users to upgrade immediately. In addition to applying the patch, security teams are advised to implement network segmentation to limit exposure, monitor RADIUS logs for anomalies, and restrict access from untrusted networks. Organizations using only TACACS+ are unaffected and may consider it as a temporary alternative until updates are applied.