CVE-2019-1672 in Web Security Appliance
Summary
by MITRE
A vulnerability in the Decryption Policy Default Action functionality of the Cisco Web Security Appliance (WSA) could allow an unauthenticated, remote attacker to bypass a configured drop policy and allow traffic onto the network that should have been denied. The vulnerability is due to the incorrect handling of SSL-encrypted traffic when Decrypt for End-User Notification is disabled in the configuration. An attacker could exploit this vulnerability by sending a SSL connection through the affected device. A successful exploit could allow the attacker to bypass a configured drop policy to block specific SSL connections. Releases 10.1.x and 10.5.x are affected.
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Analysis
by VulDB Data Team • 07/09/2023
The vulnerability identified as CVE-2019-1672 resides within Cisco Web Security Appliance WSA systems and represents a critical security flaw in the device's SSL traffic handling mechanisms. This weakness specifically impacts the Decryption Policy Default Action functionality, creating a scenario where unauthorized network access can occur despite configured security policies. The vulnerability affects Cisco WSA versions 10.1.x and 10.5.x, making these releases particularly susceptible to exploitation by remote attackers without authentication requirements. The flaw manifests when the device processes SSL-encrypted traffic under specific configuration conditions, creating an unexpected behavior that undermines the intended security posture of the appliance.
The technical root cause of this vulnerability stems from improper handling of SSL-encrypted traffic when the Decrypt for End-User Notification feature is disabled within the WSA configuration. This configuration setting typically controls whether the appliance decrypts SSL traffic for inspection purposes, but when disabled, the system fails to properly enforce the configured drop policies for SSL connections. The flaw occurs during the policy evaluation process where the appliance incorrectly processes SSL traffic that should be blocked according to the security policy, yet allows it to pass through the network. This misconfiguration creates a bypass mechanism that operates at the network layer, effectively undermining the appliance's primary function as a security gateway.
From an operational perspective, this vulnerability presents significant risks to organizations relying on Cisco WSA for network security. Attackers can exploit this weakness by simply establishing SSL connections through the affected device, requiring no authentication credentials or sophisticated attack vectors. The successful exploitation allows malicious traffic to bypass configured drop policies, potentially enabling data exfiltration, command and control communications, or other malicious activities that should have been blocked by the security infrastructure. Network administrators may remain unaware of the compromise since the traffic appears to be legitimate SSL connections passing through the device, creating a stealthy attack vector that can persist undetected within the network environment.
The security implications extend beyond simple policy bypass, as this vulnerability aligns with several ATT&CK framework techniques including T1071.004 for Application Layer Protocol: DNS and T1566 for Phishing, since the bypassed traffic could carry malicious payloads or be used for reconnaissance activities. Additionally, this vulnerability maps to CWE-284, Access Control Bypass, and CWE-312, Cleartext Storage of Sensitive Information, as it allows unauthorized access to network resources that should be protected. Organizations utilizing Cisco WSA for SSL inspection and content filtering face heightened risk of security breaches, as this vulnerability essentially creates a backdoor that can be exploited to circumvent the very security measures designed to protect their network infrastructure.
Mitigation strategies for CVE-2019-1672 require immediate attention from network security teams, including applying the relevant Cisco security patches and updates released to address this specific flaw. Organizations should also implement network segmentation and monitoring to detect anomalous SSL traffic patterns that might indicate exploitation attempts. Configuration reviews are essential to ensure that the Decrypt for End-User Notification feature is properly configured according to security best practices, and network administrators should consider disabling SSL decryption for traffic that doesn't require deep inspection. Additionally, implementing comprehensive network monitoring and logging solutions can help detect unauthorized traffic patterns that may indicate exploitation attempts, while regular security assessments should be conducted to identify similar configuration vulnerabilities across the network infrastructure.