CVE-2016-1440 in Web Security Appliance
Summary
by MITRE
The proxy process on Cisco Web Security Appliance (WSA) devices through 9.1.0-070 allows remote attackers to cause a denial of service (CPU consumption) by establishing an FTP session and then improperly terminating the control connection after a file transfer, aka Bug ID CSCuy43468.
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Analysis
by VulDB Data Team • 08/25/2022
The Cisco Web Security Appliance WSA device represents a critical component in enterprise network security infrastructure, providing proxy services that filter and inspect web traffic to protect organizations from malicious content. This vulnerability specifically targets the proxy process within the WSA software version 9.1.0-070 and earlier, creating a significant risk for organizations relying on this security appliance. The flaw manifests when the device processes FTP protocol connections, particularly during the control connection termination phase following file transfers. This issue falls under the category of resource exhaustion attacks that can severely impact network availability and operational continuity.
The technical implementation of this vulnerability involves a specific sequence of events that triggers improper resource handling within the WSA proxy process. When an attacker establishes an FTP session and subsequently terminates the control connection in an improper manner after completing a file transfer, the device fails to properly release CPU resources associated with that session. This mismanagement causes the proxy process to consume excessive CPU cycles continuously, leading to a gradual degradation of system performance and eventual complete denial of service. The flaw demonstrates poor state management and resource cleanup mechanisms within the FTP protocol handling code, which is classified as a weakness under CWE-400, specifically related to resource exhaustion vulnerabilities. The improper termination sequence creates a condition where the system enters a loop or maintains references to abandoned resources, preventing proper garbage collection and system recovery.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise entire network security operations. Organizations using affected WSA devices face the risk of complete network outages during attack periods, as the proxy process consumes all available CPU resources and becomes unresponsive to legitimate traffic. This scenario particularly affects enterprises that depend heavily on web content filtering and security monitoring, as the appliance becomes unable to process new connections or inspect traffic effectively. The vulnerability creates a window of opportunity for attackers to conduct additional malicious activities while the system remains degraded, and it can be exploited remotely without requiring authentication or specialized privileges. From an adversarial perspective, this represents a low-effort, high-impact attack vector that aligns with tactics described in the MITRE ATT&CK framework under the T1498 technique for network denial of service, making it particularly attractive to threat actors seeking to disrupt business operations.
Mitigation strategies for this vulnerability require immediate implementation of software updates from Cisco, specifically addressing the identified bug CSCuy43468 through the official security patches. Organizations should implement network monitoring solutions to detect anomalous CPU usage patterns that may indicate exploitation attempts, and establish automated alerting mechanisms for proxy process resource consumption. Network segmentation and redundant security appliances should be considered to minimize impact if the vulnerability is exploited, while also implementing proper access controls to limit exposure to unauthorized users. The vulnerability highlights the importance of maintaining up-to-date security appliances and conducting regular vulnerability assessments to identify and remediate similar issues before they can be exploited by malicious actors. Additionally, organizations should review their incident response procedures to ensure rapid detection and remediation of resource exhaustion attacks, as the symptoms may initially appear as normal system performance degradation rather than malicious activity.