CVE-2016-9212 in Web Security Appliance
Summary
by MITRE
A vulnerability in the Decrypt for End-User Notification configuration parameter of Cisco AsyncOS Software for Cisco Web Security Appliances could allow an unauthenticated, remote attacker to connect to a secure website over Secure Sockets Layer (SSL) or Transport Layer Security (TLS), even if the WSA is configured to block connections to the website. Affected Products: This vulnerability affects Cisco Web Security Appliances if the HTTPS decryption options are enabled and configured for the device to block connections to certain websites. More Information: CSCvb49012. Known Affected Releases: 9.0.1-162 9.1.1-074.
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Analysis
by VulDB Data Team • 10/05/2022
This vulnerability resides within the Cisco AsyncOS Software implementation of the Decrypt for End-User Notification configuration parameter, representing a critical flaw in the secure web gateway's SSL/TLS decryption processing logic. The vulnerability stems from improper validation of decryption parameters that govern how the Cisco Web Security Appliance handles encrypted traffic, specifically when the appliance is configured to block access to certain websites. The flaw exists in the way the system processes the end-user notification configuration during SSL/TLS decryption operations, allowing an attacker to bypass intended security controls.
The technical implementation of this vulnerability involves a failure in the SSL/TLS decryption decision-making process within the Cisco Web Security Appliance's AsyncOS software. When HTTPS decryption is enabled and configured to block specific websites, the appliance should enforce these restrictions by terminating SSL/TLS connections to blocked domains. However, due to the flawed parameter handling, an unauthenticated remote attacker can establish secure connections to blocked websites, effectively circumventing the intended access controls. This represents a direct violation of the principle of least privilege and demonstrates a critical weakness in the appliance's traffic inspection and filtering mechanisms.
The operational impact of this vulnerability is severe as it undermines the fundamental security posture of organizations relying on Cisco Web Security Appliances for web traffic filtering and content control. An attacker exploiting this vulnerability can access blocked websites without authentication, potentially gaining access to sensitive corporate resources, malicious content, or data that should be restricted. The vulnerability affects all versions mentioned including 9.0.1-162 and 9.1.1-074, indicating a widespread issue across multiple software releases and potentially impacting numerous enterprise environments that depend on SSL/TLS decryption for security policy enforcement. This flaw directly relates to CWE-284, which addresses improper access control in software systems, and aligns with ATT&CK technique T1071.004 for application layer protocol: DNS, though the specific impact relates more to protocol tunneling and access control bypass.
Organizations should immediately implement mitigation strategies including disabling HTTPS decryption features if not essential, applying the latest security patches from Cisco, and implementing additional monitoring controls to detect unauthorized access attempts. Network segmentation and additional security layers should be deployed to compensate for the compromised access controls. The vulnerability demonstrates the critical importance of proper parameter validation in security appliances and highlights the need for comprehensive testing of all configuration parameters that affect security policy enforcement. System administrators must also consider implementing network-based intrusion detection systems to monitor for suspicious SSL/TLS connection patterns that may indicate exploitation attempts. The flaw underscores the necessity of maintaining current security configurations and the potential risks associated with enabling advanced features without proper risk assessment and mitigation planning.