CVE-2015-4216 in Web Security Appliance
Summary
by MITRE
The remote-support feature on Cisco Web Security Virtual Appliance (WSAv), Email Security Virtual Appliance (ESAv), and Security Management Virtual Appliance (SMAv) devices before 2015-06-25 uses the same default SSH root authorized key across different customers' installations, which makes it easier for remote attackers to bypass authentication by leveraging knowledge of a private key from another installation, aka Bug IDs CSCuu95988, CSCuu95994, and CSCuu96630.
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Analysis
by VulDB Data Team • 05/21/2022
The vulnerability CVE-2015-4216 represents a critical authentication bypass flaw in Cisco's virtual appliance security products including Web Security Virtual Appliance WSAv, Email Security Virtual Appliance ESAv, and Security Management Virtual Appliance SMAv. This weakness stems from the improper implementation of remote support functionality that utilizes a hardcoded default SSH root authorized key across multiple customer deployments. The vulnerability specifically affects devices running software versions prior to the 2015-06-25 security update, creating a persistent security risk that spans across different organizational boundaries. The flaw enables attackers to exploit knowledge of a private key from one customer installation to gain unauthorized access to other customers' systems, fundamentally undermining the security isolation that should exist between separate deployments.
This technical weakness falls under the category of improper credential management and hardcoded credentials, which aligns with CWE-259 and CWE-798 vulnerability classifications. The implementation flaw lies in the design decision to use identical cryptographic keys across different customer environments, violating fundamental security principles of key uniqueness and isolation. The remote support feature was intended to provide administrators with convenient access for troubleshooting and maintenance purposes, but the security implications of reusing the same key across installations creates a significant attack surface. Attackers can leverage this vulnerability through passive reconnaissance or by obtaining private key materials from public sources, making the exploitation relatively straightforward and scalable across multiple targets.
The operational impact of CVE-2015-4216 extends beyond simple unauthorized access, as it enables attackers to establish persistent backdoor access to customer environments. This vulnerability directly maps to several ATT&CK techniques including T1078 Valid Accounts for legitimate credential use and T1021 Remote Services for remote access capabilities. Organizations using affected Cisco virtual appliances face potential data breaches, system compromise, and unauthorized modification of security policies. The vulnerability's widespread nature means that attackers could simultaneously target multiple customers, amplifying the impact of a single compromise. Additionally, the attack vector requires minimal technical expertise, as it relies on the predictable reuse of cryptographic materials rather than complex exploitation techniques.
Mitigation strategies for CVE-2015-4216 primarily focus on immediate software updates to the affected Cisco appliances, ensuring all devices receive the security patches released on or after 2015-06-25. Organizations should implement comprehensive key rotation procedures for all SSH access mechanisms and establish strict controls over credential distribution. The remediation process requires careful coordination of patch management across all affected appliances, with particular attention to maintaining operational continuity during updates. Network segmentation and monitoring should be enhanced to detect unauthorized SSH access attempts, while organizations must conduct thorough inventory audits to identify all affected devices. Security teams should also implement principle of least privilege controls for remote support access and establish automated monitoring for suspicious authentication patterns. The vulnerability highlights the critical importance of avoiding hardcoded credentials in production systems and emphasizes the need for proper key management practices that prevent cross-tenant credential leakage across different customer deployments.