CVE-2019-1804 in NX-OS
Summary
by MITRE
A vulnerability in the SSH key management for the Cisco Nexus 9000 Series Application Centric Infrastructure (ACI) Mode Switch Software could allow an unauthenticated, remote attacker to connect to the affected system with the privileges of the root user. The vulnerability is due to the presence of a default SSH key pair that is present in all devices. An attacker could exploit this vulnerability by opening an SSH connection via IPv6 to a targeted device using the extracted key materials. An exploit could allow the attacker to access the system with the privileges of the root user. This vulnerability is only exploitable over IPv6; IPv4 is not vulnerable.
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Analysis
by VulDB Data Team • 09/12/2023
The vulnerability identified as CVE-2019-1804 represents a critical security flaw in Cisco Nexus 9000 Series switches operating in Application Centric Infrastructure mode. This weakness stems from the improper implementation of SSH key management within the device firmware, creating a persistent backdoor that remains active across all affected systems. The vulnerability specifically affects the ACI mode switch software, which is designed for data center network virtualization and orchestration, making it particularly concerning for enterprise environments where network infrastructure security is paramount. The flaw manifests through the inclusion of a hardcoded default SSH key pair that exists in every device of this series, fundamentally undermining the security model of the device's authentication system.
The technical exploitation of this vulnerability requires an attacker to leverage IPv6 connectivity to establish an SSH session using the default key materials that are embedded within the device firmware. This implementation flaw creates a persistent access vector that does not require any authentication credentials beyond knowledge of the default key pair, which is documented in the device's software and accessible to anyone who can perform network reconnaissance. The vulnerability's design ensures that any device running the affected software version will remain susceptible to this attack regardless of network configuration or additional security measures. The default SSH key pair is stored in the device's configuration and is accessible through standard network protocols, eliminating the need for complex exploitation techniques. This vulnerability is classified under CWE-310 as a Cryptographic Vulnerability, specifically involving the use of hardcoded cryptographic keys that should never be present in production systems.
The operational impact of this vulnerability extends far beyond simple unauthorized access, as successful exploitation grants attackers complete administrative control over the affected network switch. The root privileges obtained through this attack vector allow for complete network disruption, data exfiltration, and the potential for lateral movement within the network infrastructure. Attackers could leverage this access to modify network configurations, create backdoors, or disable security controls that protect the network from further unauthorized access. The vulnerability's IPv6-only restriction does not mitigate the risk, as IPv6 networks are increasingly common in enterprise environments and often lack proper security controls. This creates a scenario where network administrators may be unaware of the vulnerability's presence, as the default SSH keys are not typically monitored or managed as part of standard security operations.
Organizations affected by this vulnerability must implement immediate mitigation strategies to prevent exploitation of the hardcoded SSH key pair. The primary recommendation involves disabling SSH access entirely or implementing strict IPv6 access controls that prevent unauthorized connections to the affected devices. Network segmentation and firewall rules should be configured to block IPv6 traffic to the switch management interfaces unless absolutely necessary. Additionally, organizations should consider implementing network monitoring solutions that can detect unauthorized SSH connections using default key materials. The vulnerability demonstrates a fundamental flaw in the device's security design and highlights the importance of proper key management practices, including the use of unique, randomly generated SSH keys for each device. Organizations should also conduct comprehensive network audits to identify all affected devices and ensure that default credentials and keys have been properly removed or replaced. This vulnerability aligns with ATT&CK technique T1021.004 for remote services and T1566 for credential harvesting, representing a significant risk to enterprise network security and requiring immediate attention from security operations teams.