CVE-2016-6437 in Wide Area Application Services
Summary
by MITRE
A vulnerability in the SSL session cache management of Cisco Wide Area Application Services (WAAS) could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition due to high consumption of disk space. The user would see a performance degradation. More Information: CSCva03095. Known Affected Releases: 5.3(5), 6.1(1), 6.2(1). Known Fixed Releases: 5.3(5g)1, 6.2(2.32).
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Analysis
by VulDB Data Team • 09/28/2022
The vulnerability identified as CVE-2016-6437 resides within the SSL session cache management functionality of Cisco Wide Area Application Services (WAAS) appliances, representing a critical denial of service weakness that can be exploited remotely without authentication. This flaw specifically targets the way WAAS handles SSL session caching mechanisms, creating a condition where an attacker can manipulate the system to consume excessive disk space resources, ultimately leading to service degradation or complete system unavailability. The vulnerability affects multiple software versions including 5.3(5), 6.1(1), and 6.2(1), with patched releases available in 5.3(5g)1 and 6.2(2.32), demonstrating the severity of the issue as it required specific patches to address the underlying problem.
The technical implementation of this vulnerability stems from inadequate resource management within the SSL session cache subsystem of WAAS appliances, where the system fails to properly limit or monitor the growth of cached session data. This weakness allows an attacker to continuously submit SSL session requests or manipulate existing session caches in a manner that causes exponential growth in disk space consumption. The flaw operates at the application layer and leverages the inherent design of SSL session caching to create a resource exhaustion condition, where legitimate system operations become impaired due to the rapid consumption of available storage space. This represents a classic example of a resource exhaustion attack pattern that can be classified under CWE-400 as "Uncontrolled Resource Consumption" and aligns with ATT&CK technique T1499.004 for "File System Wipe" and T1499.001 for "Endpoint Denial of Service" within the adversary tactics and techniques framework.
The operational impact of CVE-2016-6437 extends beyond simple service disruption to encompass significant business continuity risks for organizations relying on WAAS for application delivery and optimization. When exploited, the vulnerability can cause progressive performance degradation that may eventually lead to complete service outages, affecting critical business applications and user access. Network administrators face the challenge of monitoring disk space utilization and identifying the root cause of performance issues, as the symptoms manifest as slow response times and eventually system unavailability rather than immediate failure. The vulnerability's remote exploitability means that attackers can target affected systems from outside the network perimeter without requiring valid credentials, making it particularly dangerous for organizations with exposed WAAS appliances. Organizations may experience cascading effects where the DoS condition impacts downstream services and applications that depend on the affected WAAS infrastructure.
Mitigation strategies for CVE-2016-6437 primarily involve implementing the vendor-provided patches and updates, specifically versions 5.3(5g)1 and 6.2(2.32) which contain the necessary code modifications to address the SSL session cache management flaw. Network administrators should conduct comprehensive vulnerability assessments to identify all affected WAAS appliances and prioritize patch deployment across the enterprise network. Additional protective measures include implementing network segmentation to limit exposure of WAAS appliances to untrusted networks, monitoring disk space utilization for abnormal patterns, and establishing baseline performance metrics to quickly detect potential exploitation attempts. Organizations should also consider implementing rate limiting or session cache size restrictions as temporary workarounds while patches are deployed, though these measures may impact legitimate user sessions and application performance. The vulnerability underscores the importance of maintaining up-to-date security patches and implementing proper network monitoring to detect and respond to exploitation attempts before they can cause significant operational disruption.