Cisco Nexus Switch Vulnerability Allows Attackers to Cause DoS

Cisco Systems has disclosed a high-severity vulnerability (CVE-2025-20111) in its Nexus 3000 and 9000 Series Switches operating in standalone NX-OS mode.

The vulnerability enables unauthenticated attackers to trigger denial of service (DoS) conditions through crafted Ethernet frames.

Rated 7.4 on the CVSS v3.1 scale, the flaw affects critical infrastructure components widely used in enterprise and data center environments.

Technical Breakdown of the Vulnerability

The vulnerability stems from improper handling of specific Ethernet frames within the switches’ health monitoring diagnostics subsystem.

Attackers exploiting this flaw can send a sustained stream of malicious packets to vulnerable devices, causing unexpected reloads and prolonged service disruptions.

Unlike vulnerabilities requiring authentication or administrative access, this weakness allows adjacent attackers—those with network proximity to the target device—to execute attacks without credentials.

Cisco’s advisory clarifies that exploitation does not permit data theft or system takeover but emphasizes the operational risks of repeated device reboots.

In high-availability environments, such outages could cascade into critical application downtime, financial losses, and compliance violations.

Affected Products and Mitigation Measures

The impacted hardware includes:

• Nexus 3000 Series: 3100, 3200, 3400, and 3600 models
• Nexus 9000 Series: 9200, 9300, and 9400 switches running standalone NX-OS

Cisco has confirmed immunity for several product lines, including Nexus 7000 Series, MDS 9000 Series switches, and all Nexus 9000 devices operating in Application-Centric Infrastructure (ACI) mode.

The company has released patched software versions addressing the flaw and recommends immediate upgrades for vulnerable systems.

Workarounds such as access control list (ACL) modifications to filter malicious traffic are available for organizations unable to deploy updates promptly.

This vulnerability highlights risks inherent in network health monitoring systems, which often operate with elevated privileges.

With Nexus switches forming the backbone of many enterprise networks, widespread exploitation could disrupt healthcare and finance sectors.

Cisco’s Product Security Incident Response Team (PSIRT) has incorporated this advisory into its February 2025 FXOS/NX-OS Security Advisory Bundle—a quarterly publication detailing critical fixes for Cisco’s switching and firewall platforms.

The coordinated disclosure follows Cisco’s standard vulnerability management practices, providing network administrators with detailed upgrade paths and mitigation strategies.

Recommendations for Network Operators

1. Prioritize Patch Deployment: Apply Cisco’s fixed software releases to affected devices, available via the company’s Software Center.
2. Implement Traffic Filtering: Use ACLs to block anomalous Ethernet frames targeting the health monitoring subsystem.
3. Segment Sensitive Networks: Restrict adjacent access to Nexus switches through microsegmentation and zero-trust architectures.
4. Monitor Reload Events: Deploy network monitoring tools to track unexpected device restarts and traffic patterns indicative of exploitation attempts.

As enterprises increasingly rely on automated network infrastructures, this vulnerability underscores the importance of rigorous patch management cycles and defense-in-depth strategies.

With no publicly documented exploits at press time, proactive mitigation offers organizations a critical window to safeguard their networks against potential attacks.

For technical specifics, Cisco’s full advisory (cisco-sa-n3kn9k-healthdos-eOqSWK4g) provides configuration guidance and patching timelines.

Security teams should cross-reference their infrastructure against Cisco’s impacted products list and initiate remediation workflows to neutralize this persistent threat vector.

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