CVE-2016-6469 in Web Security Appliance
Summary
by MITRE
A vulnerability in HTTP URL parsing of Cisco AsyncOS for Cisco Web Security Appliance (WSA) could allow an unauthenticated, remote attacker to cause a denial of service (DoS) vulnerability due to the proxy process unexpectedly restarting. More Information: CSCvb04312. Known Affected Releases: 9.0.1-162 9.1.1-074. Known Fixed Releases: 10.1.0-129 9.1.2-010.
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Analysis
by VulDB Data Team • 07/05/2019
The vulnerability identified as CVE-2016-6469 represents a critical denial of service flaw within Cisco AsyncOS operating on Cisco Web Security Appliance devices. This weakness specifically targets the HTTP URL parsing functionality that processes incoming web requests through the proxy service. The flaw manifests when the proxy process experiences an unexpected restart, effectively disrupting the appliance's ability to process legitimate web traffic and maintain network security operations. The vulnerability affects specific release versions of the Cisco WSA software, namely 9.0.1-162 and 9.1.1-074, while subsequent fixed releases 10.1.0-129 and 9.1.2-010 address the underlying issue.
The technical exploitation of this vulnerability occurs through malformed HTTP URL requests that trigger a buffer overflow or parsing error within the proxy component of the AsyncOS. When an unauthenticated remote attacker crafts specific HTTP requests containing malformed URL parameters, the parsing routine fails to properly validate input data, leading to a crash of the proxy process. This process restarts automatically, creating a denial of service condition that prevents legitimate users from accessing web resources through the security appliance. The flaw demonstrates characteristics consistent with CWE-121, which describes heap-based buffer overflow conditions, and CWE-122, which covers stack-based buffer overflow scenarios that can lead to process termination.
From an operational perspective, this vulnerability presents a significant risk to organizations relying on Cisco WSA appliances for web security filtering and content inspection. The remote nature of the attack means that threat actors can exploit the flaw without requiring physical access or authentication credentials, making it particularly dangerous for network security infrastructure. The unexpected process restart creates a service disruption that can last from several seconds to minutes, depending on the appliance's recovery time, potentially affecting thousands of concurrent users. This vulnerability directly impacts the availability aspect of the CIA triad and can be categorized under ATT&CK technique T1499.100, which covers network denial of service attacks targeting network infrastructure devices.
Organizations affected by CVE-2016-6469 should immediately implement mitigation strategies including applying the patched releases 10.1.0-129 or 9.1.2-010 as recommended by Cisco. Network administrators should also consider implementing access control lists or firewall rules to limit access to the WSA appliance from suspicious sources and monitor for unusual traffic patterns that might indicate exploitation attempts. Additionally, implementing intrusion detection systems with signature-based detection for known malicious URL patterns can help identify potential exploitation attempts. The vulnerability highlights the importance of maintaining current security patches and demonstrates how seemingly minor parsing flaws in security appliances can result in significant service disruptions. Organizations should also conduct regular vulnerability assessments and penetration testing to identify similar weaknesses in their network security infrastructure and ensure proper incident response procedures are in place to handle such denial of service events.