CVE-2025-20152: Cisco Identity Services Engine DoS Flaw

CVE-2025-20152 Overview

A vulnerability in the RADIUS message processing feature of Cisco Identity Services Engine (ISE) could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to improper handling of certain RADIUS requests. An attacker could exploit this vulnerability by sending a specific authentication request to a network access device (NAD) that uses Cisco ISE for authentication, authorization, and accounting (AAA). A successful exploit could allow the attacker to cause Cisco ISE to reload, disrupting network access control services.

Critical Impact

Unauthenticated remote attackers can cause Cisco ISE to reload, resulting in denial of service for all network authentication, authorization, and accounting services dependent on the affected ISE deployment.

Affected Products

• Cisco Identity Services Engine 3.4.0
• Cisco Identity Services Engine (all versions using RADIUS message processing)

Discovery Timeline

• 2025-05-21 - CVE-2025-20152 published to NVD
• 2025-07-11 - Last updated in NVD database

Technical Details for CVE-2025-20152

Vulnerability Analysis

This vulnerability stems from improper handling of certain RADIUS requests within the Cisco Identity Services Engine. The flaw is classified as CWE-125 (Out-of-Bounds Read), indicating that the RADIUS message processing component reads data past the end of the intended buffer when parsing specific authentication requests. This out-of-bounds read operation can trigger an unrecoverable error condition, causing the ISE service to reload.

The attack requires no authentication and can be executed remotely over the network. The scope of impact extends beyond the vulnerable component itself (Changed scope), as a successful exploit disrupts authentication services for all network access devices relying on the affected ISE instance.

Root Cause

The vulnerability is rooted in an out-of-bounds read condition (CWE-125) within the RADIUS message parsing logic. When the ISE receives a specially crafted RADIUS authentication request, the processing function fails to properly validate the boundaries of incoming data before attempting to read it. This improper boundary checking allows an attacker to trigger a read operation that accesses memory beyond the allocated buffer, causing the ISE process to crash and reload.

Attack Vector

The attack is executed remotely over the network through the RADIUS protocol infrastructure. An attacker sends a malicious authentication request to a network access device (NAD) that is configured to use the vulnerable Cisco ISE for AAA services. When the NAD forwards this crafted request to the ISE for processing, the malformed RADIUS message triggers the out-of-bounds read condition. The attack requires no privileges or user interaction, and can be launched by any attacker with network access to devices that communicate with the target ISE deployment.

The exploitation process involves:

1. Identifying a network access device that uses Cisco ISE for authentication
2. Crafting a malicious RADIUS authentication request with specific malformed parameters
3. Sending the crafted request to the NAD, which forwards it to ISE
4. The ISE RADIUS processing component attempts to parse the malformed request
5. An out-of-bounds read occurs, causing ISE to reload and service disruption

Detection Methods for CVE-2025-20152

Indicators of Compromise

• Unexpected ISE service restarts or reloads without scheduled maintenance
• RADIUS authentication failures affecting multiple NADs simultaneously
• Unusual RADIUS request patterns in network access device logs
• ISE crash dump files indicating RADIUS message processing errors

Detection Strategies

• Monitor ISE system logs for unexpected restart events and correlate with RADIUS processing activity
• Implement network monitoring to detect anomalous RADIUS traffic patterns targeting ISE infrastructure
• Configure alerting for ISE availability drops that correlate with authentication service outages
• Deploy network intrusion detection rules to identify malformed RADIUS packets

Monitoring Recommendations

• Enable verbose logging on ISE RADIUS processing components to capture detailed request information
• Set up availability monitoring with short polling intervals for critical ISE nodes
• Monitor NAD authentication success/failure rates for sudden degradation patterns
• Implement centralized log aggregation to correlate ISE events across clustered deployments

How to Mitigate CVE-2025-20152

Immediate Actions Required

• Review the Cisco Security Advisory for specific patch information and affected version details
• Identify all Cisco ISE deployments in your environment running version 3.4.0 or other affected versions
• Plan emergency maintenance windows to apply security patches to ISE infrastructure
• Implement network segmentation to limit direct RADIUS access to trusted NADs only

Patch Information

Cisco has released a security advisory addressing this vulnerability. Administrators should consult the Cisco Security Advisory cisco-sa-ise-restart-ss-uf986G2Q for detailed information about fixed software versions and upgrade paths. Organizations should prioritize patching ISE deployments that handle critical authentication infrastructure.

Workarounds

• Restrict network access to ISE RADIUS services using firewall rules to allow only trusted NADs
• Implement rate limiting on RADIUS traffic to slow potential exploitation attempts
• Deploy ISE in high-availability configurations to minimize service disruption from individual node failures
• Monitor for and block suspicious authentication requests at network perimeter devices

# Example: Restrict RADIUS access using ACLs on network infrastructure
# Limit RADIUS communication to known NAD IP addresses only
# Apply ACL to ISE management interfaces

# On Cisco router/switch protecting ISE:
access-list 100 permit udp host <NAD_IP_1> host <ISE_IP> eq 1812
access-list 100 permit udp host <NAD_IP_1> host <ISE_IP> eq 1813
access-list 100 permit udp host <NAD_IP_2> host <ISE_IP> eq 1812
access-list 100 permit udp host <NAD_IP_2> host <ISE_IP> eq 1813
access-list 100 deny udp any host <ISE_IP> eq 1812 log
access-list 100 deny udp any host <ISE_IP> eq 1813 log
access-list 100 permit ip any any