CVE-2017-6679 in Umbrella Virtual Appliance
Summary
by MITRE
The Cisco Umbrella Virtual Appliance Version 2.0.3 and prior contained an undocumented encrypted remote support tunnel (SSH) which auto initiated from the customer's appliance to Cisco's SSH Hubs in the Umbrella datacenters. These tunnels were primarily leveraged for remote support and allowed for authorized/authenticated personnel from the Cisco Umbrella team to access the appliance remotely and obtain full control without explicit customer approval. To address this vulnerability, the Umbrella Virtual Appliance version 2.1.0 now requires explicit customer approval before an SSH tunnel from the VA to the Cisco terminating server can be established.
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Analysis
by VulDB Data Team • 12/11/2019
The vulnerability described in CVE-2017-6679 represents a critical security flaw in the Cisco Umbrella Virtual Appliance that compromised the principle of least privilege and explicit authorization. This issue affected versions 2.0.3 and earlier of the appliance, which contained a hidden backdoor mechanism that automatically established encrypted SSH connections to Cisco's datacenter hubs without requiring customer consent. The implementation of this undocumented feature created a significant risk where authorized Cisco personnel could gain full administrative control over customer appliances without explicit approval from the appliance owners, fundamentally undermining the security model of the appliance and violating fundamental security practices.
The technical flaw manifests as an auto-initiated remote support tunnel that operates at the network level through SSH protocol connections. This mechanism operates outside of normal user authentication processes and bypasses standard access controls that would typically require explicit user consent or administrative approval. The vulnerability falls under CWE-284, which addresses improper access control, and specifically represents a case of unauthorized access through backdoor mechanisms. The automatic nature of the tunnel establishment means that customers had no visibility into or control over when these connections were initiated, creating a persistent security risk that could be exploited by malicious actors with access to Cisco's support infrastructure.
The operational impact of this vulnerability extends beyond immediate security concerns to encompass broader implications for customer trust and compliance requirements. Organizations deploying the affected appliance were unknowingly exposing their network infrastructure to potential unauthorized access by Cisco support personnel, which could violate regulatory compliance standards such as those outlined in the NIST Cybersecurity Framework and ISO 27001. The lack of customer approval requirements meant that sensitive network configurations, logs, and potentially customer data could be accessed without proper authorization, creating audit trail issues and potential legal ramifications for organizations that rely on strict data governance policies.
The remediation implemented in version 2.1.0 addresses the core issue by requiring explicit customer approval before establishing any SSH tunnel connections between the virtual appliance and Cisco's terminating servers. This change aligns with the ATT&CK framework's concept of privilege escalation through backdoor access and ensures that all remote access operations require documented authorization. The fix demonstrates proper security engineering practices by implementing a user consent mechanism that maintains the functionality of remote support while eliminating the unauthorized access vector. Organizations should verify their appliance versions and ensure all systems are updated to version 2.1.0 or later to eliminate this vulnerability, as the previous automatic tunnel establishment mechanism created an inherent risk that could be exploited to gain complete administrative control over customer network infrastructure.