CVE-2015-6287 in Web Security Appliance
Summary
by MITRE
Cisco Web Security Appliance (WSA) 8.0.6-078 and 8.0.6-115 allows remote attackers to cause a denial of service (service outage) via a flood of TCP traffic that leads to DNS resolution delays, aka Bug IDs CSCur32005 and CSCur07907.
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Analysis
by VulDB Data Team • 12/09/2017
The Cisco Web Security Appliance WSA vulnerability identified as CVE-2015-6287 represents a significant denial of service weakness that affects specific versions of the web security platform. This vulnerability manifests when remote attackers exploit the appliance's handling of TCP traffic to create conditions that result in DNS resolution delays, ultimately leading to complete service outages. The issue impacts Cisco WSA versions 8.0.6-078 and 8.0.6-115, making these specific releases particularly susceptible to exploitation. The vulnerability operates through a sophisticated attack vector that leverages the appliance's DNS resolution mechanisms, creating a cascading failure that disrupts normal network operations and compromises the availability of security services.
The technical flaw underlying CVE-2015-6287 resides in the WSA's insufficient handling of TCP traffic patterns that trigger DNS resolution timeouts. When attackers flood the appliance with carefully crafted TCP traffic, the system's DNS resolution process becomes overwhelmed and begins to experience significant delays. This occurs because the appliance's internal DNS resolution mechanisms cannot properly manage the volume of concurrent requests generated by the attack traffic. The vulnerability specifically affects the appliance's ability to maintain stable DNS resolution services under stress conditions, creating a scenario where legitimate network traffic is disrupted. This weakness aligns with CWE-400, which categorizes the issue as an uncontrolled resource consumption problem, where the system's resources are exhausted through malicious traffic patterns that overwhelm the DNS resolution subsystem.
The operational impact of this vulnerability extends beyond simple service disruption to encompass broader security implications for organizations relying on Cisco WSA for network protection. When exploited successfully, the vulnerability can result in complete service outages that leave networks exposed to other threats while the appliance remains unavailable. The attack requires minimal sophistication to execute, making it particularly dangerous as it can be leveraged by attackers with basic networking knowledge. Organizations may experience extended downtime while the appliance recovers from the DNS resolution delays, potentially creating windows of vulnerability during which malicious traffic can bypass security controls. The disruption affects the appliance's ability to perform its primary function of filtering and inspecting web traffic, leaving network users vulnerable to threats that would normally be blocked by the security appliance.
Mitigation strategies for CVE-2015-6287 should focus on both immediate defensive measures and long-term architectural improvements. Organizations should implement rate limiting and traffic shaping policies to prevent the flood of TCP traffic that triggers the vulnerability, utilizing the appliance's built-in traffic management capabilities. Network administrators should also consider implementing intrusion prevention systems that can detect and block the specific traffic patterns associated with this attack. Cisco has released patches and updates to address this vulnerability, and organizations should prioritize applying these security updates to affected systems. Additionally, implementing redundant security appliances and load balancing configurations can help maintain service availability even when individual devices are compromised. The mitigation approach should align with ATT&CK framework tactics related to defense evasion and resource exhaustion, ensuring that defensive measures address both the immediate vulnerability and broader threat landscape considerations.