CVE-2025-20111: Cisco Nexus Switches DoS Vulnerability

CVE-2025-20111 Overview

A vulnerability in the health monitoring diagnostics of Cisco Nexus 3000 Series Switches and Cisco Nexus 9000 Series Switches in standalone NX-OS mode could allow an unauthenticated, adjacent attacker to cause the device to reload unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to the incorrect handling of specific Ethernet frames. An attacker could exploit this vulnerability by sending a sustained rate of crafted Ethernet frames to an affected device. A successful exploit could allow the attacker to cause the device to reload.

Critical Impact

Unauthenticated attackers on an adjacent network can force affected Cisco Nexus switches to reload by sending crafted Ethernet frames, causing network outages and service disruption.

Affected Products

• Cisco Nexus 3000 Series Switches (standalone NX-OS mode)
• Cisco Nexus 9000 Series Switches (standalone NX-OS mode)

Discovery Timeline

• 2025-02-26 - CVE-2025-20111 published to NVD
• 2025-02-26 - Last updated in NVD database

Technical Details for CVE-2025-20111

Vulnerability Analysis

This vulnerability resides in the health monitoring diagnostics functionality of Cisco Nexus 3000 and 9000 Series Switches operating in standalone NX-OS mode. The flaw allows an unauthenticated attacker with adjacent network access to trigger an unexpected device reload by transmitting specially crafted Ethernet frames at a sustained rate.

The vulnerability is classified under CWE-1220 (Insufficient Granularity of Access Control), indicating that the affected devices fail to properly validate or restrict the processing of certain Ethernet frames within the health monitoring subsystem. This lack of proper input validation in the health diagnostics component allows malformed frames to trigger a fault condition that results in a device crash and reload.

The attack requires no authentication and can be executed from an adjacent network segment, making it particularly dangerous in data center environments where network switches serve as critical infrastructure components.

Root Cause

The root cause of this vulnerability is the incorrect handling of specific Ethernet frames by the health monitoring diagnostics subsystem in affected NX-OS software. When the health monitoring component receives certain malformed or unexpected Ethernet frames, it fails to properly process them, leading to a condition that triggers an unexpected device reload. The insufficient input validation in this diagnostic pathway allows attackers to craft frames that exploit this processing flaw.

Attack Vector

The attack vector for CVE-2025-20111 requires adjacency to the target network. An attacker must be positioned on the same Layer 2 network segment as the vulnerable Cisco Nexus switch to successfully exploit this vulnerability. The attack methodology involves:

1. The attacker gains access to a network segment adjacent to the target Cisco Nexus switch
2. The attacker crafts specific Ethernet frames designed to trigger the vulnerability in the health monitoring diagnostics
3. These crafted frames are sent at a sustained rate to the affected device
4. The improper frame handling causes the switch's health monitoring subsystem to encounter a fault
5. The fault condition triggers an unexpected device reload, causing a denial of service

No authentication or user interaction is required to execute this attack. The sustained transmission of crafted frames can repeatedly crash the device, potentially causing prolonged network outages if the attacker maintains the attack.

Detection Methods for CVE-2025-20111

Indicators of Compromise

• Unexpected or frequent switch reboots without administrative action
• Syslog entries indicating health monitoring subsystem crashes or errors
• Unusual Ethernet frame patterns or traffic anomalies on network segments connected to Nexus switches
• Core dump files generated on affected switches indicating diagnostic subsystem failures

Detection Strategies

• Monitor network infrastructure for unexpected device reloads using SNMP traps and syslog aggregation
• Implement network traffic analysis to detect abnormal Ethernet frame patterns on switch-connected segments
• Deploy intrusion detection systems configured to alert on unusual Layer 2 traffic behavior
• Review switch logs for health monitoring errors or diagnostic subsystem crashes

Monitoring Recommendations

• Enable comprehensive logging on all Cisco Nexus 3000 and 9000 Series Switches to capture reload events
• Configure SNMP monitoring to alert on device availability changes and unexpected reboots
• Implement network segmentation monitoring to detect lateral movement or suspicious Layer 2 activity
• Establish baseline metrics for switch uptime and compare against current operational data to identify anomalies

How to Mitigate CVE-2025-20111

Immediate Actions Required

• Review the Cisco Security Advisory for specific affected software versions and patch availability
• Identify all Cisco Nexus 3000 and 9000 Series Switches in standalone NX-OS mode within your environment
• Prioritize patching for switches in critical network segments or those exposed to less trusted network zones
• Implement network segmentation to limit adjacent network access to critical switching infrastructure

Patch Information

Cisco has released security updates to address this vulnerability. Organizations should consult the Cisco Security Advisory for detailed information on affected software versions and available patches. System administrators should plan firmware updates according to their change management procedures, prioritizing switches that are accessible from less trusted network segments.

Workarounds

• Implement strict Layer 2 access controls to limit which devices can communicate directly with affected switches
• Configure port security features to restrict the number of MAC addresses allowed on switch ports
• Deploy private VLANs to isolate sensitive switching infrastructure from general network traffic
• Monitor for and block anomalous Ethernet frame traffic at network boundaries where possible