CVE-2024-20350: Cisco Catalyst Center Auth Bypass Flaw

CVE-2024-20350 Overview

A vulnerability in the SSH server of Cisco Catalyst Center (formerly Cisco DNA Center) could allow an unauthenticated, remote attacker to impersonate a Cisco Catalyst Center appliance. This vulnerability is classified as CWE-321: Use of Hard-coded Cryptographic Key, stemming from the presence of a static SSH host key across installations.

An attacker could exploit this vulnerability by performing a machine-in-the-middle (MITM) attack on SSH connections, which could allow the attacker to intercept traffic between SSH clients and a Cisco Catalyst Center appliance. A successful exploit could allow the attacker to impersonate the affected appliance, inject commands into the terminal session, and steal valid user credentials.

Critical Impact

Successful exploitation enables attackers to impersonate Cisco Catalyst Center appliances, intercept administrative SSH sessions, inject malicious commands, and harvest privileged credentials from network administrators.

Affected Products

• Cisco Catalyst Center versions 1.0.0 through 2.3.7.4
• Cisco Catalyst Center airgap deployments (multiple versions)
• Cisco DNA Center (legacy naming) - all versions prior to the fixed release

Discovery Timeline

• September 25, 2024 - CVE-2024-20350 published to NVD
• July 30, 2025 - Last updated in NVD database

Technical Details for CVE-2024-20350

Vulnerability Analysis

This vulnerability represents a fundamental cryptographic implementation flaw where Cisco Catalyst Center appliances ship with an identical static SSH host key across all installations. The SSH protocol relies on unique host keys to establish server identity and prevent impersonation attacks. When multiple devices share the same host key, an attacker who obtains this key can impersonate any affected appliance.

The attack requires network positioning that allows the attacker to intercept SSH traffic between legitimate clients and the Catalyst Center appliance. This could be achieved through ARP spoofing, DNS poisoning, BGP hijacking, or physical access to network infrastructure. Once positioned, the attacker presents the static host key to connecting clients, which accept it as legitimate since it matches the expected key.

Root Cause

The root cause is the use of a hard-coded cryptographic key (CWE-321) in the SSH server implementation. Rather than generating unique SSH host keys during installation or first boot, the Cisco Catalyst Center software uses a pre-configured static key embedded in the distribution. This design decision eliminates the cryptographic assurance that SSH host key verification is intended to provide.

The static key is present across all affected versions from 1.0.0 through 2.3.7.4, including standard deployments, airgap installations, and MDNAC variants. This widespread distribution means any attacker who extracts the key from one appliance can potentially attack all vulnerable installations.

Attack Vector

The attack vector is network-based and requires the attacker to achieve a machine-in-the-middle position between SSH clients and the Catalyst Center appliance. The attack complexity is high because it requires this specific network positioning, but no privileges or user interaction are required once the attacker is positioned.

The exploitation flow proceeds as follows: First, the attacker obtains the static SSH host key, either by extracting it from a controlled Catalyst Center instance or through other means. Next, the attacker positions themselves in the network path between administrators and the target appliance using techniques such as ARP spoofing on local networks or DNS manipulation. When an administrator initiates an SSH connection, the attacker intercepts the connection and presents the static host key. Since the key matches what the client expects, the connection proceeds without warning. The attacker can then relay traffic to the legitimate appliance while logging credentials and injecting commands.

Detection Methods for CVE-2024-20350

Indicators of Compromise

• Unexpected SSH host key changes detected by clients connecting to Catalyst Center
• ARP table anomalies indicating potential spoofing activity on network segments containing Catalyst Center
• DNS resolution discrepancies for Catalyst Center hostnames pointing to unexpected IP addresses
• SSH session logs showing connections from unusual source IP addresses or at unusual times

Detection Strategies

• Monitor for ARP spoofing attempts on network segments where Catalyst Center appliances reside using tools like arpwatch or IDS signatures
• Implement SSH host key pinning on administrative workstations and alert on any key mismatch events
• Deploy network-based intrusion detection to identify MITM attack patterns such as duplicate MAC addresses or gratuitous ARP packets
• Review SSH authentication logs on Catalyst Center for anomalous login patterns or failed authentication attempts

Monitoring Recommendations

• Enable verbose logging on SSH servers and forward logs to a SIEM for correlation analysis
• Implement network flow analysis to detect unusual traffic patterns between administrative subnets and Catalyst Center
• Configure alerting for any SSH host key verification failures reported by managed SSH clients
• Conduct regular audits of network infrastructure configurations to identify potential MITM opportunities

How to Mitigate CVE-2024-20350

Immediate Actions Required

• Apply the security update from Cisco that regenerates unique SSH host keys for each appliance
• Audit all Cisco Catalyst Center appliances to identify affected versions and prioritize patching
• Implement network segmentation to restrict SSH access to Catalyst Center from dedicated management networks only
• Configure SSH client strict host key checking and verify current host key fingerprints against known-good values

Patch Information

Cisco has released a security update to address this vulnerability. Administrators should consult the Cisco Security Advisory for specific fixed versions and upgrade paths. The patch generates unique SSH host keys during installation, eliminating the shared key vulnerability.

After applying the patch, administrators must distribute new host key fingerprints to all SSH clients that connect to Catalyst Center, as the regenerated keys will differ from previously cached values.

Workarounds

• Restrict SSH access to Catalyst Center appliances using firewall rules or access control lists to limit connections to trusted management subnets
• Implement jump hosts or bastion servers as the sole entry point for SSH administration, reducing the attack surface for MITM attempts
• Deploy 802.1X network access control on management VLANs to prevent unauthorized device placement
• Consider using out-of-band management networks physically isolated from production traffic where feasible

# Example: Restrict SSH access using firewall rules (adapt to your environment)
# Allow SSH only from trusted management subnet
iptables -A INPUT -p tcp --dport 22 -s 10.0.100.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 22 -j DROP