CVE-2015-6290 in Web Security Appliance
Summary
by MITRE
Cisco Web Security Appliance (WSA) 8.0.7 allows remote HTTP servers to cause a denial of service (memory consumption from stale TCP connections) via crafted responses, aka Bug ID CSCuw10426.
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Analysis
by VulDB Data Team • 12/19/2017
The Cisco Web Security Appliance WSA version 8.0.7 contains a critical vulnerability that enables remote attackers to consume excessive memory resources through crafted HTTP responses, leading to denial of service conditions. This vulnerability specifically affects the appliance's handling of stale TCP connections, where improperly managed connection states can accumulate and exhaust available memory resources. The issue manifests when remote HTTP servers send specially crafted responses that trigger the WSA to maintain stale connection states indefinitely, creating a memory leak scenario that can eventually render the appliance unusable.
The technical flaw resides in the WSA's connection management logic within its HTTP processing module. When the appliance receives HTTP responses from remote servers, it fails to properly clean up stale TCP connections that should be terminated after a certain period of inactivity. This weakness allows attackers to exploit the connection tracking mechanism by sending responses that contain specific headers or content patterns that cause the WSA to maintain connection state information without proper timeout handling. The vulnerability is classified as a memory exhaustion issue that operates at the transport layer, specifically affecting TCP connection state management and resource cleanup processes.
The operational impact of this vulnerability is severe as it can completely disrupt network security operations by rendering the WSA appliance non-functional. Organizations relying on Cisco WSA for web security filtering, content inspection, and threat prevention face significant risks when this vulnerability is exploited. The memory consumption from stale connections can gradually increase until the appliance reaches its memory limits, causing system instability, application crashes, or complete service outages. This denial of service condition affects not only the appliance itself but also the entire network security infrastructure that depends on its proper operation, potentially leaving organizations vulnerable to other threats while the appliance is offline.
Mitigation strategies should include immediate patch application to upgrade to Cisco WSA versions that address this vulnerability, typically those released after the vulnerability disclosure. Network administrators should also implement connection timeout configurations to reduce the window of opportunity for exploitation, monitor memory usage patterns for unusual increases, and establish automated alerting for connection state anomalies. The vulnerability aligns with CWE-400, which covers "Uncontrolled Resource Consumption" and relates to ATT&CK technique T1499.004 for "Endpoint Denial of Service" and T1595.001 for "Network Denial of Service. Organizations should also consider implementing network segmentation to limit the impact of potential exploitation and maintain detailed logging of connection states to detect anomalous behavior patterns that may indicate attempted exploitation of this vulnerability.