CVE-2019-1817 in Web Security Appliance
Summary
by MITRE
A vulnerability in the web proxy functionality of Cisco AsyncOS Software for Cisco Web Security Appliance could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability is due to improper validation of HTTP and HTTPS requests. An attacker could exploit this vulnerability by sending a malformed HTTP or HTTPS request to an affected device. An exploit could allow the attacker to cause a restart of the web proxy process, resulting in a temporary DoS condition.
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Analysis
by VulDB Data Team • 09/12/2023
The vulnerability identified as CVE-2019-1817 resides within the web proxy functionality of Cisco AsyncOS Software operating on Cisco Web Security Appliances, representing a critical security flaw that compromises system availability. This issue stems from inadequate validation mechanisms within the software's handling of HTTP and HTTPS protocol requests, creating an exploitable weakness that can be leveraged by remote attackers without requiring authentication credentials. The affected devices operate under the assumption that incoming requests will conform to expected protocol standards, but the software fails to properly sanitize or validate these requests before processing them through the web proxy component. This fundamental flaw in input validation creates a pathway for malicious actors to manipulate the device's operational state through carefully crafted malformed requests.
The technical exploitation of this vulnerability occurs through the injection of malformed HTTP or HTTPS requests that specifically target the web proxy processing module within the Cisco Web Security Appliance. When the system receives these crafted requests, the insufficient validation causes the web proxy process to encounter unexpected data structures or protocol violations that trigger an internal error condition. The software's failure to properly handle these edge cases results in the automatic restart of the web proxy service, which temporarily disrupts the device's ability to filter and inspect web traffic. This restart operation effectively creates a denial of service condition that impacts the appliance's core functionality, as it cannot process incoming web requests until the proxy service recovers and resumes normal operations.
From an operational impact perspective, this vulnerability presents a significant risk to organizations that rely on Cisco Web Security Appliances for network traffic filtering and security enforcement. The temporary nature of the DoS condition means that while the disruption is not permanent, it creates windows of vulnerability where malicious traffic can bypass security controls during the proxy service restart period. Network administrators face the challenge of maintaining consistent security posture while dealing with intermittent service interruptions that can occur without warning. The vulnerability affects the availability aspect of the CIA triad by compromising the system's ability to provide continuous service, potentially allowing attackers to repeatedly exploit the flaw to create sustained disruption. Organizations with limited network security monitoring capabilities may struggle to detect these DoS events, as they occur through normal protocol interactions rather than obvious malicious traffic patterns.
The vulnerability aligns with CWE-20, which describes improper input validation as a fundamental weakness in software security design. This classification emphasizes that the root cause lies in the software's failure to properly validate or sanitize input data before processing it through critical system functions. From an attacker's perspective, this vulnerability maps to multiple ATT&CK techniques including T1499.004 for endpoint denial of service and T1595.001 for network infiltration through protocol manipulation. The lack of authentication requirements makes this particularly dangerous as it can be exploited by any remote attacker with network access to the appliance, potentially allowing for reconnaissance activities to identify vulnerable targets. Organizations should consider implementing network segmentation to limit access to these appliances, while also monitoring for unusual traffic patterns that might indicate exploitation attempts. The vulnerability highlights the importance of robust input validation mechanisms and proper error handling within network security appliances to prevent exploitation through protocol manipulation. Cisco has released patches addressing this vulnerability through security updates that improve the validation of HTTP and HTTPS requests within the web proxy functionality, requiring organizations to implement these updates promptly to maintain their security posture.