CVE-2016-6416 in Email Security Appliance
Summary
by MITRE
The FTP service in Cisco AsyncOS on Email Security Appliance (ESA) devices 9.6.0-000 through 9.9.6-026, Web Security Appliance (WSA) devices 9.0.0-162 through 9.5.0-444, and Content Security Management Appliance (SMA) devices allows remote attackers to cause a denial of service via a flood of FTP traffic, aka Bug IDs CSCuz82907, CSCuz84330, and CSCuz86065.
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Analysis
by VulDB Data Team • 09/21/2022
The vulnerability described in CVE-2016-6416 represents a critical denial of service weakness affecting multiple Cisco security appliances including Email Security Appliance ESA, Web Security Appliance WSA, and Content Security Management Appliance SMA. This flaw exists within the FTP service implementation of the AsyncOS operating system version 9.6.0-000 through 9.9.6-026 for ESA devices, 9.0.0-162 through 9.5.0-444 for WSA devices, and affects the corresponding SMA versions. The vulnerability stems from insufficient input validation and resource management within the FTP service handling mechanism, creating a pathway for malicious actors to exploit the system through crafted network traffic patterns.
The technical exploitation of this vulnerability occurs when remote attackers flood the affected devices with excessive FTP traffic, overwhelming the system resources and causing the FTP service to become unresponsive or crash entirely. This type of attack specifically targets the protocol handling components within the Cisco AsyncOS environment, where the system fails to properly manage concurrent connections or resource allocation during high-volume FTP traffic scenarios. The flaw manifests as a failure to properly implement rate limiting or connection throttling mechanisms, allowing attackers to consume system resources at an unsustainable rate. According to CWE classification, this vulnerability aligns with CWE-400, which covers "Uncontrolled Resource Consumption" or "Resource Exhaustion" conditions that can lead to denial of service attacks.
The operational impact of CVE-2016-6416 is severe for organizations relying on Cisco security appliances for network protection, as it can result in complete service disruption for email, web, and content security functions. When exploited successfully, the vulnerability can render critical security infrastructure non-operational, leaving networks exposed to other threats while security monitoring and protection capabilities are compromised. The attack vector is particularly concerning because it requires minimal technical expertise to execute, making it accessible to a broad range of threat actors including script kiddies and organized attack groups. From an ATT&CK framework perspective, this vulnerability maps to T1499.004 which covers "Cloud Service Scanning" and T1498 which covers "Network Denial of Service," demonstrating how this weakness can be leveraged for broader operational disruption campaigns.
Organizations affected by this vulnerability should immediately implement mitigation strategies including network segmentation to isolate affected appliances, deployment of firewall rules to limit FTP traffic access, and implementation of connection rate limiting measures where possible. Cisco released security advisories and patches addressing this specific issue, recommending immediate firmware upgrades to versions that contain the necessary fixes. The mitigation approach should also include monitoring for unusual FTP traffic patterns and implementing intrusion detection systems to identify potential exploitation attempts. Additionally, organizations should conduct comprehensive vulnerability assessments to identify other potential denial of service vulnerabilities within their network infrastructure, as similar resource exhaustion patterns may exist in other components of the security ecosystem. The remediation process requires careful planning to minimize service disruption while ensuring complete vulnerability resolution across all affected appliance models and software versions.