CVE-2025-20163: Cisco Nexus Dashboard Auth Bypass Flaw

CVE-2025-20163 Overview

A vulnerability in the SSH implementation of Cisco Nexus Dashboard Fabric Controller (NDFC) could allow an unauthenticated, remote attacker to impersonate Cisco NDFC-managed devices. This vulnerability is due to insufficient SSH host key validation, enabling attackers to perform machine-in-the-middle attacks on SSH connections to NDFC-managed devices.

Critical Impact

Successful exploitation allows attackers to impersonate managed network devices and capture user credentials, potentially compromising the entire fabric controller infrastructure.

Affected Products

• Cisco Nexus Dashboard Fabric Controller (NDFC)
• Cisco Nexus Dashboard (all affected versions)
• NDFC-managed network devices via SSH connections

Discovery Timeline

• 2025-06-04 - CVE CVE-2025-20163 published to NVD
• 2025-07-22 - Last updated in NVD database

Technical Details for CVE-2025-20163

Vulnerability Analysis

This vulnerability stems from insufficient SSH host key validation within the Cisco Nexus Dashboard Fabric Controller. When NDFC establishes SSH connections to managed devices, the system fails to properly validate the host keys presented by those devices. This cryptographic weakness allows an attacker positioned between NDFC and its managed devices to intercept and manipulate SSH traffic without detection.

The attack requires network positioning capabilities but does not require authentication or user interaction. A successful exploit has significant cross-scope impact, potentially affecting both confidentiality and integrity of communications between the management platform and network infrastructure devices.

Root Cause

The root cause is classified as CWE-322: Key Exchange without Entity Authentication. The NDFC implementation lacks proper verification of SSH host keys when establishing connections to managed devices, creating a trust relationship without cryptographic validation of the remote entity's identity.

Attack Vector

An attacker exploits this vulnerability by positioning themselves in the network path between Cisco NDFC and its managed devices (machine-in-the-middle position). When NDFC initiates SSH connections to managed switches or routers, the attacker intercepts these connections and presents their own SSH host key. Due to insufficient validation, NDFC accepts the attacker's key as legitimate, allowing the attacker to:

1. Intercept all SSH traffic between NDFC and managed devices
2. Impersonate managed devices to the NDFC controller
3. Capture administrator credentials transmitted during SSH sessions
4. Potentially inject malicious commands into the management stream

The attack requires high complexity due to the network positioning requirement, but once achieved, it provides complete visibility into management communications without requiring any prior authentication or privileges.

Detection Methods for CVE-2025-20163

Indicators of Compromise

• Unexpected SSH host key changes reported during NDFC-to-device communications
• Anomalous network traffic patterns between NDFC and managed switches/routers
• Authentication failures followed by successful logins from different network segments
• SSH session logs showing connections from unexpected intermediate IP addresses

Detection Strategies

• Monitor SSH host key fingerprints for managed devices and alert on unexpected changes
• Implement network traffic analysis to detect potential MITM positioning between NDFC and managed infrastructure
• Review NDFC connection logs for anomalous SSH session establishment patterns
• Deploy intrusion detection rules to identify SSH key negotiation anomalies

Monitoring Recommendations

• Enable comprehensive logging of all SSH connections from NDFC to managed devices
• Configure alerts for SSH host key mismatch events in the network management infrastructure
• Monitor for ARP spoofing or other Layer 2 attacks that could enable MITM positioning
• Implement continuous network path validation between NDFC and critical managed devices

How to Mitigate CVE-2025-20163

Immediate Actions Required

• Apply the security patch from Cisco as soon as available for your NDFC version
• Review the Cisco Security Advisory for specific remediation guidance
• Audit current SSH host key configurations and document known-good fingerprints for all managed devices
• Implement network segmentation to limit potential MITM attack surfaces

Patch Information

Cisco has released a security advisory addressing this vulnerability. Administrators should consult the Cisco Security Advisory cisco-sa-ndfc-shkv-snQJtjrp for specific patch versions and upgrade instructions applicable to their deployment.

Workarounds

• Implement strict network segmentation between NDFC and managed devices to reduce MITM attack surfaces
• Use out-of-band management networks with restricted physical and logical access for NDFC communications
• Deploy network monitoring solutions to detect potential MITM attacks on management traffic
• Consider temporary manual verification of SSH host keys until patches can be applied

# Example: Verify SSH host key fingerprints manually before connections
# Document known-good fingerprints for all managed devices
ssh-keyscan -t rsa,ecdsa,ed25519 <managed-device-ip> | ssh-keygen -lf -

# Monitor for ARP table anomalies that could indicate MITM positioning
arp -a | grep <ndfc-ip-range>