CVE-2015-0628 in Web Security Appliance
Summary
by MITRE
The proxy engine on Cisco Web Security Appliance (WSA) devices allows remote attackers to bypass intended proxying restrictions via a malformed HTTP method, aka Bug ID CSCus79174.
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Analysis
by VulDB Data Team • 07/15/2017
The vulnerability identified as CVE-2015-0628 affects Cisco Web Security Appliance devices and represents a significant security flaw in the proxy engine implementation. This weakness enables remote attackers to circumvent the intended proxying restrictions that are typically enforced by the appliance to control and monitor web traffic. The vulnerability specifically manifests through the manipulation of HTTP methods in requests sent to the WSA device, allowing unauthorized access to resources that should otherwise be restricted or filtered by the security appliance's proxy functionality. The issue is particularly concerning as it undermines the fundamental security posture of organizations relying on Cisco WSA for web traffic filtering and content inspection.
The technical flaw resides in the proxy engine's insufficient validation of HTTP methods received from client requests. When processing HTTP requests, the WSA device fails to properly validate or sanitize the HTTP method field, which can contain malformed or unexpected method names. This inadequate input validation allows attackers to craft specially crafted HTTP requests that exploit the proxy engine's parsing logic, enabling bypass of access controls and content filtering mechanisms. The vulnerability specifically leverages the HTTP method field in a way that the device's proxy engine does not properly handle, potentially allowing access to restricted resources or bypassing security policies that should prevent such access. This type of vulnerability falls under the CWE-20 category of "Improper Input Validation" and represents a classic case of insufficient sanitization of user-supplied data in network security appliances.
The operational impact of CVE-2015-0628 extends beyond simple access control bypass, potentially allowing attackers to access restricted websites, download malicious content, or circumvent content filtering policies that organizations have implemented for security and compliance reasons. Organizations using Cisco WSA devices may experience unauthorized access to corporate resources, exposure of sensitive data, or potential redirection to malicious websites that would normally be blocked by the appliance's filtering capabilities. The vulnerability's remote exploitability means that attackers do not require physical access to the network or device, making it particularly dangerous for organizations that rely on the appliance for perimeter security. This weakness can be exploited as part of broader attack chains, potentially leading to further compromise of the network infrastructure or data exfiltration from the organization's environment.
Mitigation strategies for this vulnerability should include immediate application of Cisco's security patches and updates that address the proxy engine validation issue. Organizations should also implement network segmentation and monitoring to detect anomalous HTTP traffic patterns that might indicate exploitation attempts. The vulnerability's characteristics align with ATT&CK technique T1071.004 for Application Layer Protocol: DNS and T1071.001 for Application Layer Protocol: Web Protocols, indicating potential use in reconnaissance and exploitation phases. Network administrators should also consider implementing additional security controls such as deep packet inspection, web application firewalls, and enhanced logging to detect and prevent exploitation attempts. Regular security assessments and vulnerability scanning should be conducted to identify similar weaknesses in other network security appliances and ensure comprehensive protection against similar vulnerabilities.