CVE-2016-10259 in SSL Visibility
Summary
by MITRE
Blue Coat SSL Visibility (SSLV) 3.x before 3.11.3.1 is susceptible to a denial-of-service vulnerability that impacts the SSL servers for intercepted SSL connections. A malicious SSL client can, under certain circumstances, temporarily exhaust the TCP connection pool of an SSL server.
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Analysis
by VulDB Data Team • 08/28/2020
The vulnerability identified as CVE-2016-10259 affects Blue Coat SSL Visibility appliances running version 3.x before 3.11.3.1, representing a critical denial-of-service weakness that specifically targets SSL server functionality. This issue stems from inadequate handling of SSL connections within the interception process, creating a scenario where malicious actors can exploit the system's TCP connection management mechanisms. The vulnerability operates by leveraging specific characteristics of SSL client behavior to manipulate the connection pool resources, ultimately leading to service disruption for legitimate users. The impact extends beyond simple availability issues as it directly affects the core functionality of SSL visibility appliances that are designed to monitor and analyze encrypted traffic flows within network environments.
The technical flaw manifests through improper resource management within the SSL server component of the appliance, specifically in how it handles concurrent TCP connections during SSL interception processes. When a malicious SSL client establishes connections with specific parameters or patterns, it can trigger a condition where the appliance's connection pool becomes temporarily exhausted. This occurs because the system fails to properly implement connection lifecycle management or resource allocation controls that would normally prevent such exhaustion scenarios. The vulnerability is particularly concerning as it operates at the protocol level where SSL/TLS connections are being intercepted and analyzed, making it difficult to distinguish between legitimate and malicious traffic patterns without proper detection mechanisms. According to CWE classification, this represents a weakness in resource management where insufficient controls over connection pooling lead to resource exhaustion, specifically categorized under CWE-400 as "Uncontrolled Resource Consumption" with potential implications for CWE-1321 "Improper Resource Shutdown or Release".
The operational impact of this vulnerability extends beyond simple service disruption as it creates a potential attack vector that can be exploited by adversaries to compromise network visibility capabilities. Organizations relying on Blue Coat SSL Visibility appliances for security monitoring and compliance enforcement may find their ability to analyze encrypted traffic severely compromised during an attack. The temporary nature of the connection pool exhaustion means that legitimate users may experience intermittent service degradation rather than complete outages, making detection and response more challenging. This vulnerability directly impacts the appliance's ability to maintain continuous SSL interception services, potentially creating blind spots in network security monitoring that could be exploited by attackers to bypass security controls. The attack requires minimal sophistication and can be executed remotely, making it particularly dangerous in environments where SSL visibility is critical for threat detection and compliance monitoring. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving resource exhaustion and service disruption, specifically mapping to T1499.004 for "Endpoint Denial of Service" and potentially T1566.002 for "Phishing with Malicious Attachment" if attackers leverage it as part of broader attack chains.
Mitigation strategies for CVE-2016-10259 should focus on immediate patching of affected appliances to version 3.11.3.1 or later, which contains the necessary fixes for connection pool management. Network administrators should also implement connection rate limiting and monitoring mechanisms to detect anomalous connection patterns that may indicate exploitation attempts. Additionally, organizations should consider implementing network segmentation to limit the impact of potential exploitation and ensure that SSL visibility appliances are properly isolated within the network architecture. Configuration hardening practices should include implementing proper TCP connection timeouts and connection reuse controls to prevent the accumulation of stale connections that could contribute to pool exhaustion. The vulnerability highlights the importance of proper resource management in security appliances and underscores the need for robust testing of resource handling mechanisms in high-availability systems that process sensitive network traffic. Regular vulnerability assessments and penetration testing should include evaluation of connection pool management and resource consumption patterns to identify similar weaknesses in other security infrastructure components.